Geology and Geomorphology 44 and Geomorphology.pdf · Mesophotic coral ecosystems · Coral reef · Geomorphology · Relict topography · Sedimentary dynamics 44.1 nI troduction Reef

849© Springer Nature Switzerland AG 2019Y. Loya et al. (eds.), Mesophotic Coral Ecosystems, Coral Reefs of the World 12, https://doi.org/10.1007/978-3-319-92735-0_44

Geology and Geomorphology

Clark E. Sherman, Stanley D. Locker, Jody M. Webster, and David K. Weinstein

Abstract

Geomorphology and geological processes exert funda-mental controls on the occurrence, distribution, and makeup of mesophotic coral ecosystems (MCEs). Two broad geomorphic categories are shelves and slopes. Shelves include outer portions of continental and insular shelves that dip gently into mesophotic depths before reaching the shelf break and have very low gradients (<1°). Other low-gradient habitats include tops of isolated banks. Slope habitats extend from platform breaks down into adjacent basins and can be divided into low-gradient slopes (<30°), steep slopes (~30 to 70°), and walls (>70°). On shelves, MCEs are best developed on positive relief features elevated above the surrounding seafloor. In slope settings, MCE development is typically favored on steep irregular slopes, where coral cover is concentrated on steep-sided buttresses and sediment is channelized into narrow chutes. Relict features related to past sea levels are critically important MCE habitats on both shelves and slopes. Coral and coralline algae remain the primary frame builders in MCEs. However, accretion at mesophotic depths is likely very slow, such that they form only thin

biostromal veneers over relict substrates. Sediments in MCEs are dominantly autochthonous skeletal sands and gravels. Although fluxes of sediments to the seafloor in MCEs are typically lower than in shallow reefs, sedimen-tary dynamics still play an important role. Low-gradient seafloor has an increased potential for accumulation of sediment detrimental to MCEs. In slope settings, downslope bed-load transport of sediment can be orders of magnitude higher than vertical fluxes and likely exerts an important influence on MCEs.

KeywordsMesophotic coral ecosystems · Coral reef · Geomorphology · Relict topography · Sedimentary dynamics

44.1 Introduction

Reef systems have long been known to extend to depths well beyond 30 m. In seminal works describing the zonation and geomorphology of Jamaican reefs, the (upper) deep fore-reef (with scleractinian frame) was described as extending to depths of 55–75 m (Goreau and Goreau 1973; Goreau and Land 1974). Working in Belize, James and Ginsburg (1979) preferred the term reef front to refer to the zone extending from the highest point on a reef profile (crest) down to a point where little or no skeletal frame building occurs, typi-cally ~70 to 100 m (see also Tucker and Wright 1990; James and Bourque 1992). Not surprisingly, however, the majority of reef studies have focused on environments shallower than ~30 m given the logistical and technological difficulties accessing deeper settings (Hinderstein et al. 2010). Thus, our knowledge of deeper reef systems lags well behind that of their shallow counterparts. Over the last decade or more, there has been a renewed interest and focus on deeper reef systems at depths of ~50 to 100 m. This has been fostered by

C. E. Sherman (*) Department of Marine Sciences, University of Puerto Rico, Mayagüez, PR, USAe-mail: [email protected]

S. D. Locker College of Marine Science, University of South Florida, St. Petersburg, FL, USA

J. M. Webster Geocoastal Research Group, School of Geosciences, The University of Sydney, Sydney, NSW, Australia

D. K. Weinstein The Fredy & Nadine Herrmann Institute of Earth Science, The Hebrew University of Jerusalem, Jerusalem, Israel

The Interuniversity Institute for Marine Sciences in Eilat, Eilat, Israel

Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA

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advances in and application of technical diving (Pyle 1996; Sherman et al. 2009, 2013a), as well as remote sensing to map, sample, and estimate the extent of deep habitats (Locker et al. 2010; Bridge et al. 2012a). The term “mesophotic coral ecosystem” (MCE) has been adopted to refer to these deeper reef settings. Specifically, MCEs are defined as light-depen-dent corals and associated benthic communities found at depths from 30 to 40 m and extending to depths of 100–150 m or roughly the base of the photic zone (Lesser et al. 2009; Hinderstein et al. 2010; Kahng et al. 2010).

MCEs may represent deep extensions of shallow reef sys-tems, such as shelf-margin reefs around the Caribbean (Goreau and Goreau 1973; Goreau and Land 1974; James and Ginsburg 1979; Liddell et al. 1997; Liddell and Ohlhorst 1988; Sherman et al. 2010). Alternatively, they may occupy more isolated banks with no direct connection to shallower systems, such as MCEs in the Gulf of Mexico (Hine et al. 2008; Locker et al. 2010, 2016), Great Barrier Reef (GBR; Harris et al. 2013; Bridge et al. 2019), Northwest Australia (Heyward and Radford 2019), and the Philippine Sea (Nacorda et al. 2017). MCEs are often dynamic transition zones between shallow shelves and deep ocean basins in terms of biological communities, sedimentary facies, and physical oceanographic processes. Given their proximity to open-ocean conditions, MCEs can be exposed to oceanographic factors atypical of shallow reef settings, such as the impingement of internal waves and associated fluctuations in the thermocline, nutrients, turbidity, the passage of warm- and cold-core eddies, and deep currents that can run counter to prevailing shallow, wind-driven currents (Wolanski et al. 2004; Bridge et al. 2011a). Relict topography, often related to past sea levels, plays an important role in determining the occurrence and distribution of MCEs. Relict features, such as submerged reefs, are not only important MCE habitats but also represent key geological archives of oceanographic and climatic change and the response of reef systems to these changes. Herein, we provide a general overview of the geology and geomorphology of MCEs. The aim is to establish consistent patterns in the geologic and geomorphic characteristics of MCEs, as well as to identify important geological processes that influence their occurrence, distribution, depositional characteristics, and incorporation into the rock record.

44.2 Tectonic Settings

MCEs occur worldwide where environmental and oceano-graphic conditions amenable to coral growth interface with hard-bottom substrates suitable for larval settlement. This chapter presents a number of geologic settings and morphol-ogies that support MCEs, ranging from broad low- gradient continental shelves to the high-relief slopes of volcanic islands. A first-order control on geomorphic habitat style is

the plate tectonic setting. Passive or trailing-edge margins may develop broad shelves (e.g., Australia and the Gulf of Mexico) or carbonate banks (Bahamas) that are large spa-tially, but continental runoff or environmental variability (e.g., temperature and salinity) can restrict suitable locations for MCE development, especially along inner shelf zones. Conversely, outer portions of shelves and their steep margins may be sufficiently isolated from coastal influences, such as terrigenous influx, and exposed to oceanic currents that promote desirable conditions for MCEs.

Broad passive-margin shelves typically have deep shelf breaks of 70–100 m or more (Carter and Johnson 1986; Harris and Davies 1989; Hine et al. 2008; Abbey et al. 2011a), resulting in large areas of the shelf at mesophotic depths (Fig. 44.1). For example, based solely on depth (30–100 m), Locker et al. (2010) indicate that the passive-margin shelf of the northern Gulf of Mexico/Florida region has an order of magnitude greater potential area (178,867 km2) than either the US Caribbean (3892 km2) or main Hawaiian Islands (3299 km2). An assessment of submerged banks (mean depth of ~27 m) on the GBR continental shelf by Harris et al. (2013) indicates that they have a combined area of 25,600 km2, representing potential MCE habitat with a distribution along the shelf similar to that of shallow reefs. Of this area, predictive habitat modeling indicates that more than half (~14,000 km2) is suitable habitat for coral communities (Harris et al. 2013). While the overall development of continental shelves is a response to sea-level change over millions of years, complex relict topography produced by the most recent Quaternary sea-level fluctuations plays a significant role in shaping morphology that supports contemporary MCE development.

Active margins associated with convergent subduction zones and transform plate boundaries include areas of volcanism and vertical tectonics that promote narrower insular margins often characterized by steep relief (e.g., Western Pacific and the Caribbean). Narrow insular shelves typically have relatively shallow shelf breaks at depths of ~20 to 30 m (Goreau and Land 1974; Hubbard et al. 2008; Sherman et al. 2010), resulting in MCE habitats being located primarily on steep marginal slopes (Fig. 44.1). Additionally, given their closer proximity to shore, MCEs on narrow shelves are more likely to be impacted by terrigenous inputs. Mid-plate and divergent margin volcanism also pro-duce island chains that can be sourced from both hot spots (e.g., Hawaiʻi, Tahiti, and the Galapagos) and divergent plate boundaries (e.g., Bermuda and Trinidad). MCEs in insular settings may benefit from more oligotrophic oceanographic conditions in contrast to more eutrophic conditions associ-ated with riverine input to inner continental shelves. There is still much unknown about the spatial abundance of MCE habitat. Rates of discovery are higher for insular margins, albeit having reduced geographic area, in contrast to broad shelves that host MCEs distributed across large areas that are

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poorly mapped (Locker et al. 2010; Rooney et al. 2010). In our discussion, we review these relationships based on two geomorphic styles: (1) continental/insular shelves and (2) continental/insular (marginal) slopes.

44.3 Relict Topography and Sea-Level Change

44.3.1 Late Quaternary Sea-Level Change

Over the latter part of the Quaternary period (~500 ka to present), climate and sea level have rhythmically oscillated, with a periodicity of ~100,000 years, between warm inter-glacial highstands within approximately ±10 m of present and cold glacial lowstands with sea levels at approximately 120 ± 10 m below present (Shackleton 1987; Rohling et al. 2009, 2014). These fluctuations in sea level have played a fundamental role in shaping the antecedent topography upon which both shallow and mesophotic reef systems are built. The most recent cycle of glacio-eustatic sea-level change is depicted in Fig. 44.2. Following the last interglacial period centered at ~125 ka when sea level was 6–9 m above present (Kopp et al. 2009; Dutton and Lambeck 2012), sea level gradually oscillated downward to the last glacial maximum at ~21 ka when sea level was ~125 to 135 m below present (Lambeck and Chappell 2001; Yokoyama et al. 2001; Siddall et al. 2003; Hanebuth et al. 2009; Lambeck et al. 2014). The last deglaciation began between 20 and 21 ka, and sea level rose rapidly until approximately 5–6 ka, marking the end of major ice sheet decay (Lambeck and Chappell 2001; Siddall et al. 2003; Lambeck et al. 2014). Thus, modern

MCE habitats have been shaped both by gradually falling sea levels leading into glacial lowstands and rapidly rising sea levels during deglaciations. Each process can leave behind relict features, such as submerged reefs and shorelines that are indicative of past sea levels and can be important sites of MCE development.

Various geological records, including submerged relict reefs, indicate that sea-level rise during the last deglaciation was not smooth and continuous but punctuated by several brief periods of accelerated rise associated with a surge in glacial meltwater runoff, i.e., a meltwater pulse (MWP; e.g., Fairbanks 1989). However, not all records agree on the exis-tence or timing of all of these events. The earliest is the 19 ka MWP, which signified the end of the last glacial maximum. At that time, sea level rose 10–15 m over an interval of 500–800 years (Yokoyama et al. 2001; Hanebuth et al. 2009). MWP-1A is well established in numerous records and is thought to have resulted in up to 20 m of sea- level rise in less than 500 years (Fairbanks 1989; Bard et al. 1990, 1996; Webster et al. 2004), though its timing is somewhat debated. Locker et al. (1996) proposed more detailed variations in the rate of MWP-1A sea-level rise that produced lithified paleo-shoreline ridges that are likely a worldwide geomorphic habitat supporting MCEs. Based on radiometric ages of sub-merged relict reefs on the insular slope of Barbados, MWP-1A was placed at ~14 ka (Fairbanks 1989; Bard et al. 1990). This age was later supported by a reef-core record from Tahiti (Bard et al. 1996). Subsequent coring in Tahiti, as well as dating of drowned reef terraces off the island of Hawaiʻi, has suggested a somewhat older age for MWP-1A of 14.6–14.7 ka (Webster et al. 2004; Deschamps et al. 2012; Sanborn et al. 2017). Evidence for the existence of MWP-1B

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Fig. 44.1 General tectonic and geomorphic settings of MCEs. Passive margins tend to have broad shelves with deep shelf breaks, resulting in large shelf areas at mesophotic depths. Active and insular margins tend to have narrower shelves with shallow shelf breaks, resulting in mesophotic habitats occurring largely on steep marginal slopes. Banks can occur across a range of depths and tectonic settings. Arrows indicate general direc-tions of sediment transport that exerts an important influence on MCEs

44 Geology and Geomorphology

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is less consistent. MWP-1B was identified as a reef-drown-ing event in Barbados occurring at ~11 ka (Fairbanks 1989; Bard et al. 1990), although it is not apparent in records from other locations, suggesting that the event was smaller than suggested by the Barbados record, if it occurred at all (Bard et al. 1996, 2010).

Blanchon and Shaw (1995) proposed an additional melt-water pulse occurring at ~7.6 ka (“CRE3”), which has subse-quently been referred to as MWP-1C (e.g., Woodroffe and Webster 2014). The timing and magnitude of this event were originally based upon the depth and age of drowned Acropora palmata reefs in the Caribbean-Atlantic region (Blanchon and Shaw 1995). Subsequently, additional evidence of reef drowning and rapid sea-level rise at this time has been identi-fied at Grand Cayman (Blanchon et al. 2002), off the coast of southeast Florida (Banks et al. 2008), the Gulf of Carpentaria

(Harris et al. 2008), Maui, Hawaiʻi (Engels et al. 2004; Fletcher et al. 2008), and Lord Howe Island (Woodroffe et al. 2010). Additionally, there is a well- documented cli-matic event at ~8 ka associated with a large influx of glacial meltwater to the North Atlantic (Alley and Agustsdottir 2005). Rapid sea-level rise identified in the stratigraphy of deltas has been attributed to this event (Törnqvist et al. 2004; Tornqvist and Hijma 2012). However, other reef records (e.g., Hubbard et al. 2008) and well- established Holocene sea-level curves based upon both reef and mangrove data (Toscano and Macintyre 2003) do not indicate rapid sea-level rise at this time. Thus, questions remain regarding the nature of sea-level change during this period.

44.3.2 Relict Topography and MCEs

Relict features formed during past periods of lower sea level are important MCE habitats on both shelves and slopes. They may be formed by erosional processes, con-structional processes, or some combination of the two. Constructional processes form positive relief features, such as relict reefs, which occur as ridges, pinnacles, and banks on shelves and low-gradient slopes. Importantly, these antecedent features provide topographically high, rocky substrates elevated above deleterious effects of sediment accumulation and are prime sites for MCE development (Bridge et al. 2011a; Locker et al. 2016). Erosional pro-cesses can form notches, wave-cut platforms, and escarp-ments resulting in prominent breaks in slope along shelf margins that are also important loci of MCE development (Locker et al. 2010). Submarine terraces are also associated with past sea levels but can have complex origins (Fletcher et al. 2008; Sherman et al. 2014). Terraces may be formed during periods of stable or slowly changing sea level allow-ing for extended erosion by waves. Alternatively, they may represent reef terraces (i.e., constructional features) subse-quently stranded by changing sea levels (Woodroffe and Webster 2014; Mulder et al. 2017).

MCEs on the continental shelf surrounding the Gulf of Mexico are closely linked to relict features formed during periods of lower sea level (Locker et al. 2010). Most of these are linear paleoshoreline ridges and mounds that tend to occur along slope trends along with small banks (Locker et al. 1996, 2016). They are thought to have formed in marginal- to shallow-marine settings during the last deglaciation and then subsequently drowned during periods of rapid sea-level rise. The Sticky Grounds on the west Florida Shelf are some of the deepest structures at depths of 116–135 m. These are thought to represent glacial lowstand structures such as oyster reefs (Locker et al. 2016). The slightly shallower, 70–100 m depth, Pinnacles Reef Trend in the northeastern Gulf of Mexico may have a similar origin. It

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is hypothesized that significant influx of glacial meltwater to the Gulf during the deglaciation could have created variable salinity conditions conducive to the development of oyster bars in coastal settings. Pulley Ridge, located at the southern end of the west Florida Shelf, is thought to be a drowned bar-rier island complex formed early in the last deglaciation. The lithified barrier island now supports a rich mesophotic com-munity at depths of 60–75 m dominated by platy scleractin-ian corals, coralline algae, and leafy green algae (Fig. 44.3; Jarrett et al. 2005; Hine et al. 2008; Reed et al. 2019). The Florida Middle Grounds on the west Florida Shelf is a group-ing of submerged ridges and isolated banks at depths of 25–45 m that also supports diverse MCE communities (Hopkins et al. 1977; Coleman et al. 2004). Previously thought to represent drowned late Quaternary coral reefs (Hine et al. 2008; Locker et al. 2010 and references therein), more recent work suggests an alternative history (Reich et al. 2013; Mallinson et al. 2014). Coring shows that some of the features consist of unconsolidated marine calcareous sedi-ment capped by a vermetid-gastropod boundstone with radiocarbon ages of ~8 to 9 ka (Reich et al. 2013). The pres-ence of vermetid gastropods and lack of corals along with geomorphic and seismic data suggest that the Ten Thousand Islands and Everglades of southwest Florida may be a mod-ern analogue for the banks (Mallinson et al. 2014). Combined results suggest the features formed in a marginal- to shallow-marine setting in the early Holocene and were subsequently drowned by rising sea levels after 8 ka (Reich et al. 2013; Mallinson et al. 2014).

Marginal slopes around the Caribbean display numerous relict features associated with periods of lower sea level during the late Quaternary. A deep escarpment extending from depths of 55–65 m down to 120–160 m or more, depending on the locale, is a common feature on many Caribbean slopes and is likely related to erosional processes occurring during glacial periods of lower sea level (Goreau and Land 1974; James and Ginsburg 1979; Liddell and Ohlhorst 1988; Ginsburg et al. 1991; Sherman et al. 2010; Rankey and Doolittle 2012; Mulder et al. 2017). Numerous submerged ridges and terraces have been identified on marginal slopes around the Caribbean that now represent important MCE habitats (e.g., Macintyre et al. 1991). The most conspicuous of these are ridge and terrace features at depths of ~50 to 90 m off the west coast of Barbados (Macintyre et al. 1991), the southwest coast of Puerto Rico (Sherman et al. 2010), western Guiana, and the north coast of Jamaica (Macintyre 2007; Macintyre et al. 1991 and references therein). Coring of submerged ridges off the south coast of Barbados by Fairbanks (1989) showed that the features at this locale are relict shallow-water reefs with a framework dominated by Acropora palmata and other shallow-water coral species. Radiometric dating of the Barbados cores indicates that these reefs formed during the

last deglaciation and were subsequently drowned by rapidly rising sea levels associated with MWP-1A (~14 ka) and MWP-1B (~11.3 ka) (Fairbanks 1989; Bard et al. 1990). Similar coring and dating efforts are needed to determine the age and history of other deep (i.e., MCE) relict features in the Caribbean.

Submerged ridges, pinnacles, and terraces are also impor-tant MCE habitats on the GBR (Fig. 44.4; Abbey et al. 2011a; Bridge et al. 2011a, b, 2012a). Harris et al. (2013) proposed a classification of banks on the outer GBR shelf on the basis of their geomorphic characteristics. Type 1 banks have a mean height of 44 m, a mean depth of 27 m, and support near-sea-surface (NSS) coral reefs (i.e., reefs that reach depths <20 m). Thus, they are co-located with shallow reefs. They are also the largest (mean area 21 km2) and most com-mon of the banks studied. Type 2 banks occur landward of the shelf-edge barrier reef on the middle and outer shelf. They are much smaller (mean area of 2 km2) and have a mean height of 26 m and a mean depth of 27 m, but do not support NSS coral reefs. Type 3 banks occur on the outer shelf, often seaward of the barrier reef. They are of intermediate size (mean area of 8.5 km2), have a mean height of 36 m, a mean depth of 56 m, and do not have NSS coral reefs. Based on their geomorphology, submerged terraces, pinnacles, and ridges have been interpreted as relict fringing, patch, and barrier reefs, respectively (Abbey et al. 2011a). Terraces are found at variable depths but most consistently occur at ~90 and 100 m. Extensive, flat-topped ridges, interpreted as mature barrier reefs, occur within a restricted depth range of 50–70 m. Discontinuous peaked ridges and pinnacles, interpreted as juvenile reefs, occur over a broader depth range of ~40 to 75 m. The preponderance of extensive ridges, i.e., mature reefs, at 50–70 m is thought to be related to the depth of repeated low-amplitude (<20 m) eustatic sea- level oscillations during the Middle to Late Pleistocene (Abbey et al. 2011a). In particular, low-amplitude sea-level rise events promote vertical reef accretion without initiating reef drowning (Abbey et al. 2011a). Thus, the most extensive MCE habitats across the GBR are directly related to past sea- level change and the response of reef systems to those changes.

The Integrated Ocean Drilling Program (IODP) Expedition 325 drilled three transects of cores across the GBR shelf margin focusing on the submerged barrier reef structures at depths of 40–45 m, as well as the prominent terraces at depths of 80–130 m (Fig. 44.4; Webster et al. 2011, 2018; Yokoyama et al. 2011; Camoin and Webster 2014). Results confirmed that these are relict features composed of two basic chronostratigraphic sequences including a basal unit > MIS 3 (~30 ka) and overlying MIS 2 to last deglacial coral reef deposits. The reef deposits are analogous to modern environments and characteristic of shallow reef crest to deeper reef slopes. In most cases, cores


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Fig. 44.3 Example of MCE habitat on the Pulley Ridge drowned barrier island complex on the southern end of the west Florida Shelf. Note that modern coral cover has not modified the antecedent geomorphology. (a) Location is 250 km west of Cape Sable. (b) Multibeam bathymetry show-ing distinctive barrier island geomorphology. (c) Agariciidae plate corals at this location growing in 65 m water depth appear to be just a thin deposit that does not alter underlying geomorphology. (d) Boomer seismic-reflection profile illustrating the Late Pleistocene-Holocene section of coastal deposition during the last sea-level rise (Jarrett et al. 2005). The basal transgressive surface is inferred based on onlapping stratigraphy that distinguishes the uppermost seismic sequence

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show deepening upward coral-algal successions representing classic reef-drowning signatures (Fig. 44.5; Webster et al. 2011, 2018; Camoin and Webster 2014).

Submerged banks, covering an area of at least 300 km2, with potential for MCEs have also been described in the Gulf of Carpentaria, northern Australia (Harris et al. 2008; Harris 2016). The banks rise from depths of ~45 to 50 m with relatively flat tops that cluster at depths of ~27 and 30 m. They exhibit geomorphic features characteristic of reefs including raised rims, relatively flat interiors (i.e., lagoon floors), and spur and groove structures along their margins. Coring of the banks indicates that they are relict shallow- water reefs that formed from ~10 to 9.5 ka and accreted upward for ~2000 years. Accretion ceased at most sites by ~8 ka with little accretion or alteration of the relict topogra-phy since that time. Modern coral growth was observed on three of the seven banks studied, but modern framework reef growth was not found at any of the sites (Harris et al. 2008; Harris 2016). A similar study by Woodroffe et al. (2010)

described a relict reef at depths of 25–50 m surrounding Lord Howe Island off southeastern Australia. Coring and radiometric dating of the structure indicate that the reef accreted from 9 to 7 ka. The authors conclude that the feature represents a relict barrier reef occurring at or close to sea level around Lord Howe Island by ~9 ka. The reef accreted upward but at rates insufficient to keep pace with sea-level rise and drowned by 7 ka (Woodroffe et al. 2010). Two cores recovered at a water depth of 34 m (their site 15) indicate ~1 m of accretion occurring at this depth since ~2.4 ka, pos-sibly providing evidence of recent MCE accretion. Additionally, Linklater et al. (2016) documented high coral cover at mesophotic depths at Balls Pyramid located ~25 km to the southeast of Lord Howe Island.

In the Hawaiian Islands, MCEs are concentrated on relict rocky structures elevated above influences of sediment accu-mulation. In many cases, these are the outer portions of sub-marine terraces associated with Quaternary sea-level changes (Fletcher and Sherman 1995; Fletcher et al. 2008; Rooney

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Fig. 44.5 Representative deepening upward succession of sediment facies and coral-algal assemblages from a submerged reef on the GBR shelf. Coralgal boundstones from the Middle and Top sections are characteristic of shallow and deeper reef frameworks, respectively. (From Camoin and Webster 2014 )


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et al. 2008, 2010). Extensive MCEs in the ‘Au‘au Channel between the islands of Maui and Lānaʻi are associated with another type of relict topography. During glacial lowstands, the Hawaiian Islands of Maui, Lānaʻi, and Molokaʻi were interconnected by limestone bridges, creating a super-island known as Maui Nui (Grigg et al. 2002). During these epi-sodes of subaerial exposure, an irregular karstic topography was generated consisting of basins, ridges, and pinnacles (Torresan and Gardner 2000; Grigg et al. 2002). Recent mesophotic coral cover, dominated by Leptoseris spp., is concentrated on topographic highs generated by these karstic processes.

44.4 General Geologic and Geomorphic Settings

MCE habitats can be divided into two broad geomorphic cat-egories: shelves and slopes (Fig. 44.1; Locker et al. 2010). The slope of the seafloor affects levels of irradiance and sed-imentary dynamics, both of which play fundamental roles in shaping MCEs (Liddell and Ohlhorst 1988; Ohlhorst and Liddell 1988; Liddell et al. 1997; Bridge et al. 2011a). A shelf is defined by the International Hydrographic Organization (IHO) as the flat or gently sloping region adja-cent to a continent or around an island that extends from the low waterline to a depth where there is a marked increase in downward slope, i.e., the shelf break (IHO 2013). Shelves are characterized by very low gradients, typically <1° (Kennett 1982). Given their depth, MCEs are generally restricted to the outer portions of continental and insular shelves that dip gently into mesophotic depths before reach-ing the shelf break. Other similar horizontal or nearly hori-zontal habitats include the planar tops of isolated banks that rise into mesophotic depths. Smaller-scale horizontal habi-tats can include marine terraces superimposed on steep shelf and bank margins (Abbey et al. 2013). A slope is defined as the sloping region that deepens from a shelf to the point where there is a general decrease in gradient (IHO 2013). Slopes are characterized by high gradients and boundaries with relatively flat shelves or banks that are abrupt (Kennett 1982). Slope habitats can refer to the steep margins of both shelves and isolated banks. Smaller-scale, high-gradient habitats include the steep sides of ridges and pinnacles built upon shelves or large banks (Abbey et al. 2013).

44.4.1 Continental and Insular Shelves

Although continental and insular shelves represent the larg-est areas that may potentially support MCEs (Locker et al. 2010; Bridge et al. 2012a; Harris et al. 2013), broad low-relief/rugosity areas typically do not support extensive

MCEs. In contrast, well-developed MCEs on shelves are generally restricted to submerged ridges and pinnacles built upon outer portions of shelves, such as the outer northeastern continental shelf of Australia/GBR (Abbey et al. 2011a, 2013; Bridge et al. 2011a, 2012a; Harris et al. 2013), the continental shelf bordering the Gulf of Mexico (Jarrett et al. 2005; Locker et al. 2010, 2016), and the Puerto Rico-Virgin Islands (PR-VI) Platform south of the US Virgin Islands (Smith et al. 2010, 2016; Weinstein et al. 2014). Low-relief areas between topographic highs tend to accumulate sediment and are therefore not conducive to coral recruitment and growth (Bridge et al. 2011a).

The broad continental shelf of the GBR off northeastern Australia gently slopes to depths of 70–100 m before reaching the shelf break (Carter and Johnson 1986; Harris and Davies 1989; Abbey et al. 2011a) and represents an extensive area of tropical seafloor at mesophotic depths. A series of submerged linear ridges parallel to the shelf edge interspersed with pinnacles and separated by sandy areas extend for hundreds of kilometers along the outer GBR shelf and represent prime habitats for MCEs (Fig. 44.4; Hopley 2006; Abbey et al. 2011a; Bridge et al. 2011a, b, 2012a). These features have been interpreted to be submerged relict reefs formed during periods of lower sea level with ridges representing barrier reefs and pinnacles representing patch reefs (Harris and Davies 1989; Beaman et al. 2008; Abbey et al. 2011a). The submerged reefs provide corals and other sessile benthos suitable hard substrate elevated above surrounding sandy areas and the effects of sedimentation. Mesophotic scleractinian coral growth, including branching species, is concentrated and most diverse on the flatter tops of submerged reefs at depths <60 m. The steeper sides of these features contain lower coral diversity composed primarily of flattened plate and encrusting growth forms. With light availability as a limiting factor for MCEs, the flatter tops of submerged reefs provide maximum irradiance, while reduced light availability on steep slopes limits coral growth (Bridge et al. 2011a, b).

The continental shelf bordering the Gulf of Mexico is another area of extensive potential MCE habitat. However, MCEs in the region may be limited by turbidity, including outflow of the Mississippi River, and seasonal temperature fluctuations (Locker et al. 2010). Once again, locations of known MCEs are associated with antecedent topographic features superimposed on the broad, gently sloping shelf. In the northern Gulf of Mexico, positive relief generated by salt domes along with suitable water conditions has resulted in development of MCEs on numerous structures, such as the Flower Garden Banks (Rezak et al. 1985; Schmahl et al. 2008). Coral cover on the banks is high (~50%) and extends from the shallowest bank tops at ~17 m down to ~46 m. Along the eastern margins of the Gulf of Mexico, MCEs are found on drowned banks, pinnacles, and paleoshoreline


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Fig. 44.6 MCEs south of St. Thomas, US Virgin Islands. (a) Habitat (geomorphology) classification of MCEs in the Red Hind Marine Conservation District (RHMCD) as defined by Smith et al. (2010). All habitats without coral have low relief. (b) Bathymetry of the RHMCD with 10x vertical exaggeration. Bathymetry from NOAA Center for Coastal Monitoring and Assessment and Rivera et al. (2006)

structures associated with lower sea levels during the late Quaternary (Hine et al. 2008; Locker et al. 2010, 2016). These include the Pinnacles Reef Trend, Florida Middle Grounds, the Sticky Grounds, and Pulley Ridge, among oth-ers (Hine et al. 2008; Locker et al. 2010, 2016).

At upper mesophotic depths of ~30 to 50 m in the Caribbean, shelf habitats can support well-developed MCEs with relatively high coral cover, such as those found to the south of the US Virgin Islands on the outer PR-VI Platform (Fig. 44.6; Smith et al. 2019). These reefs occur as a pair of linear ridges ~5 m high extending along the shelf margin and


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separated by a narrow sand channel (Smith et al. 2010, 2016; Weinstein et al. 2014). A scattered group of smaller, more irregularly shaped MCEs occur landward of the shelf mar-gin. These shallow MCEs are characterized by high coral cover (>30%) dominated by Orbicella spp. that create a complex three-dimensional habitat. At depths beyond ~50 m, Orbicella is much less common in the Caribbean (García- Sais 2010; Sherman et al. 2010, 2016), and MCEs in hori-zontal habitats are typically less developed. These deeper planar habitats, in the 50–100 m depth range, occur primarily on the tops of isolated banks, such as Bajo de Sico in the Mona Passage and Grappler Bank to the south of Puerto Rico. They are characterized by a low-relief, low-rugosity rubbly substrate with patchy occurrences of plate corals, pri-marily Agaricia spp. Algae and sponges are the dominant live benthic cover in these settings (Sherman and Appeldoorn 2015). In deeper, relatively flat to low-gradient habitats, rho-doliths (algal nodules) are often a dominant component of the seafloor rubble (Fig. 44.7) and provide important hard substrate for sessile benthic macrofauna such as algae, sponges, and corals (Macintyre et al. 1991; Locker et al. 2010; Sherman and Appeldoorn 2015).

44.4.2 Continental and Insular Slopes

Slope environments occur along the relatively steep mar-gins of shelves and banks. Shelf margins typically face open- ocean environments and are directly exposed to long-period, high-energy waves, as well as storm- and tide-gen-erated currents. Thus, they are important zones of physical energy absorption (Hine and Mullins 1983). Marginal slopes are also dynamic shallow-to-deep transitions zones

of sedimentary facies, biological communities, and physi-cal processes and provide conduits through which shelf materials are transported to deeper water (Hine and Mullins 1983). Much of the early information on MCEs (well before MCE was a recognized term) comes from descriptions of shelf- margin reef systems in the Caribbean from the shelf break to the limits of coral growth at locales such as Belize (James and Ginsburg 1979), Jamaica (Goreau and Land 1974; Moore et al. 1976; Liddell and Ohlhorst 1988), and the Bahamas (Ginsburg et al. 1991; Liddell et al. 1997). Slope settings present unique challenges to corals and other sessile benthos. The steep gradients reduce availability of light for phototrophic nutrition and facilitate downslope transport of sediment that can damage or cover sessile organisms. In light of these factors, Sherman and Appeldoorn (2015) qualitatively divided slope habitats along the southern margin of the PR-VI Platform into three general categories (Fig. 44.8): low-gradient slopes (<30°), steep slopes (~30 to 70°), and walls (>70°), each of which provides a unique combination of light availability and downslope sediment transport.

44.4.2.1 Lateral Geomorphic Trends Along Shelf Margins

As shelf margins typically face open-ocean settings, their morphology can be influenced by a degree of exposure to seas and storms. Sherman et al. (2010) documented a sys-tematic relationship between exposure of the shelf margin of southwest Puerto Rico to prevailing seas and the geomor-phology of the upper insular slope from the shelf break at ~20 m to depths of ~90 m (Fig. 44.9). Portions of the margin more exposed to prevailing southeasterly seas have a gentler gradient (~29°) and a topography consisting of widely

Fig. 44.7 (a) Irregular algal nodule colonized by Agaricia agaricites/humilis recovered from ~64 msw at Grappler Bank located south of Puerto Rico (cf. Sherman et al. 2013a). (b) Cross-sectional view of same nodule showing internal concentric structure


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spaced, rounded buttresses separated by open, low- relief slopes. These low-gradient slopes also exhibit a pronounced terrace at depths of ~80 m. In contrast, portions of the margin more sheltered from prevailing seas are consistently steeper (~44°) with more closely spaced buttresses separated by nar-row, steep-sided, sand-floored chutes resulting in a more irregular and heterogeneous topography. Along these steeper margins, the general geomorphic trend can be interrupted by near-vertical landslide scars several hundred meters across that add to both the steepness and irregularity of the topogra-phy due to fissures and slumped blocks.

Colin et al. (1986) found that the slope of Enewetak Atoll, Marshall Islands, was also steeper on leeward faces versus windward faces. Blanchon and Jones (1997) described a similar trend along the shelf margin of Grand Cayman where shelf-edge reef fronts along exposed windward margins have a gentler gradient than those along leeward margins. Strong currents and oscillatory wave flow established during storms and large-swell events are capable of pruning shelf-edge reefs and flushing sand and rubble from the shelf edge down to deeper zones on the slope (Hubbard et al. 1981; Hubbard 1992; Blanchon and Jones 1997). Coarse reef detritus sup-plied to the upper slope by pruning and scouring of shelf- edge reefs facilitates progradation (i.e., lateral seaward accretion) of the reefs and a gentler seaward gradient (Blanchon and Jones 1997). In contrast, lower energy along leeward and protected margins results in enhanced vertical accretion and a steeper seaward front. However, these steep fronts may be more prone to mass wasting as evidenced by landslide scars, which tend to be more common along steep, protected margins (Sherman et al. 2010).

The GBR shelf margin displays a larger-scale latitudinal change in morphology that greatly affects available MCE habitat. In the north, from approximately 11–17° S, the shelf

margin is very steep with long, linear, shallow reefs occur-ring along the shelf edge forming a true barrier-reef system with narrow submerged reefs on their seaward side (Hopley et al. 2007; Beaman et al. 2008). The slope is very steep in this region becoming a vertical wall below depths of ~70 m, providing little space for the development of submerged reefs and MCEs. South of 17° S, the shelf margin has a much gentler gradient with shallow reefs set back from the shelf edge. The gently sloping margin seaward of the shallow reefs has allowed for the development of an extensive series of linear submerged reefs that now support important MCEs (Hopley et al. 2007; Abbey et al. 2011a; Bridge et al. 2011a, 2012a).

44.4.2.2 Slope Gradients and MCEsOn slopes, MCEs are subject to persistent downslope trans-port of sediment generated primarily by prolific growth of coral and calcareous algae and associated carbonate produc-tion at the shelf edge. The gradient and topography of mar-ginal slopes greatly affect downslope transport (Hubbard 1992) and thus can exert a fundamental control on the occurrence and distribution of well-developed MCEs. Low- gradient slopes (<30°), typically associated with more exposed settings, tend to have lower topographic relief and rugosity with a rubbly substrate (Sherman et al. 2010; Sherman and Appeldoorn 2015). Lower slope gradient and rugosity lead to downslope sediment transport being spread over a broader area, such as a sheet flow, resulting in higher sand cover (Sherman et al. 2010, 2016). These factors, in turn, can inhibit coral recruitment and growth (Yoshioka and Yoshioka 1989; Yoshioka 2009). Thus, low-gradient slopes often have limited to moderate MCE development that is concentrated along breaks in slope gradient. Terraces super-imposed on slopes similarly have few MCEs. Although lower

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gradient slopes and terraces provide increased irradiance, they can also be subject to sediment accumulation and typically exhibit lower benthic cover (Liddell and Ohlhorst 1988; Liddell et al. 1997; Sherman et al. 2010, 2016; Bridge et al. 2011a).

In contrast, steep/high-gradient slopes (~30 to 70°), typi-cally associated with more sheltered settings, tend to have steep, irregular topography consisting of large buttresses separated by narrow grooves (Fig. 44.10). In these settings, downslope sediment transport is channelized into narrow sand chutes. Accordingly, mesophotic coral cover is typi-cally high on steep slopes and concentrated on steep-sided

buttresses and other topographic highs. These features effec-tively shed sediment, are elevated above the surrounding sea-floor, and, thus, further removed from the influence of downslope sediment movement (Liddell and Ohlhorst 1988; Liddell et al. 1997; Sherman et al. 2010, 2016). In these steep habitats, corals are predominantly either plate and encrusting forms or side-attached plates consistent with adaption to a light-limited environment. Since MCEs can be susceptible to sedimentation, many plates consist of interlocking branches that act against sediment deposition (Bridge et al. 2011a; Muir and Pichon 2019).

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Fig. 44.9 Comparison of geomorphology of exposed versus sheltered slopes along the insular shelf margin of southwest Puerto Rico. (a) Multibeam bathymetry image of insular shelf margin showing low- gradient exposed slope with pronounced terrace at ~80 to 90 msw and steep-sheltered slope with no terrace. Prevailing wave direction from the southeast. (b) Average profiles of exposed (southeast-facing) slopes and shel-tered (southwest-facing slopes) along the insular shelf margin of southwest Puerto Rico. (Adapted from Sherman et al. 2010)


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Deep buttresses occurring below the shelf break and extending from depths of ~45 to 65 m are common on Caribbean slopes including Belize (James and Ginsburg 1979), Jamaica (Goreau and Land 1974), and Puerto Rico (Sherman et al. 2010). Although the buttresses are similar to shallower, shelf-edge spur and groove structures in occur-rence and orientation, they are typically larger in scale and more widely spaced. It is unclear if these features are reflec-tive of recent MCE accretion or are relict features formed during periods of lower sea levels (Sherman et al. 2010). Roberts et al. (1977) related differences in scale and mor-phology of shallow and deep spur and groove features on Grand Cayman to a transition from wave-dominated to cur-rent-dominated settings. Further studies, including coring, are required to determine their accretionary history. Regardless, deep buttresses represent prime habitats for well-developed MCEs.

Although MCEs are better developed on steep versus low-gradient slopes, there are limits to slope gradients con-ducive to MCE development. Wall habitats refer to those set-tings where slope gradient exceeds ~70° resulting in a near-vertical to overhanging profile. Walls typically consist

of a series of irregular and discontinuous ledges often cov-ered in fine sediment. Between the ledges, bare rock or caves may be present. In these settings, irradiance levels are greatly reduced (Liddell and Ohlhorst 1988; Ohlhorst and Liddell 1988), which can cause coral recruitment to shift to horizon-tal substrates (Brakel 1979). Ledges and other low- angle sur-faces are subject to burial by sediments offsetting the advantages of increased irradiance. Thus, mesophotic walls typically have low coral cover and limited MCE develop-ment (Liddell and Ohlhorst 1988; Ohlhorst and Liddell 1988; Liddell et al. 1997). However, walls can support high abun-dances of non-photosynthetic taxa such as octocorals (e.g., Bridge et al. 2019). Many marginal slopes in the Caribbean exhibit a steep escarpment starting at depths ranging from 30 to 90 m and dropping precipitously to depths of 120–160 m or more. Typically, the escarpment begins at depths of 55–65 m at the seaward margin of deep buttresses, such as on the slopes of Jamaica and Belize (Goreau and Land 1974; James and Ginsburg 1979). On the Grand Bahama Bank, the escarpment starts as shallow as 30 m (Ginsburg et al. 1991), while off southwest Puerto Rico, it begins at ~90 m (Sherman et al. 2010). The beginning of the deep escarpment often

Fig. 44.10 Steep-slope habitat off southwest Puerto Rico. Note deep buttresses with high coral cover separated by narrow sand chute. (Photo credit: H. Ruíz)


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marks the local limit of vigorous mesophotic coral growth with a sharp decline in coral cover at this depth (Liddell and Ohlhorst 1988; Liddell et al. 1997; Sherman et al. 2010). Goreau and Goreau (1973) referred to this feature as “the final drop-off.” These deep escarpments are likely related to erosional processes occurring during past periods of lower sea level (Goreau and Land 1974; Liddell and Ohlhorst 1988).

44.5 MCE Framework and Frame Builders

44.5.1 Primary Frame Builders in MCEs

Understanding of the internal structure and composition of shallow reef systems has been gleaned from studies of emer-gent Quaternary reefs (e.g., Mesolella 1967; Mesolella et al. 1970; Chappell 1974; Pandolfi et al. 1999) and coring of modern/Holocene reefs (e.g., Macintyre 1988, 2007; Hubbard et al. 1997, 2005, 2008, 2013; Dullo 2005; Montaggioni 2005; Montaggioni and Braithwaite 2009). Unfortunately, for the most part, similar studies on MCEs have not been conducted. The few descriptions of fossil MCEs are largely restricted to much older systems (e.g., Morsilli et al. 2012; Pomar et al. 2017; Zapalski et al. 2017) and difficult to directly relate to modern MCEs. Coring of MCEs is logistically challenging for obvious reasons. Ship- based coring of reef structures at mesophotic depths has been attempted at only few locales, including Barbados (Fairbanks 1989), Tahiti (Camoin et al. 2007), and Australia (Harris et al. 2008; Woodroffe et al. 2010; Yokoyama et al. 2011). Results from these studies indicate that the cored features are largely relict and composed of shallow-water coral-algal assemblages formed during the last deglaciation between about 6 and 20 ka. These, in turn, may be built upon older Pleistocene foundations. Deep-water coral-algal communi-ties with interpreted paleowater depths of >20–30 m have been identified in the upper sections of some cores and in dredged samples from mesophotic depths (Abbey et al. 2011b, 2013) and provide some information on MCE frame-work and accretion. In other settings, we are largely limited to descriptions of benthic cover and must infer what lies below. Thus, our current understanding of mesophotic frame-work and accretion is poor compared to shallow reefs, and this remains a significant knowledge gap in our understand-ing of these systems.

On the basis of surveys of benthic cover, as well as the limited examples where true MCE framework has been recovered through coring or dredging, corals and coralline algae remain the primary frame builders in MCEs. In the Caribbean and Gulf of Mexico, mesophotic coral communi-ties are dominated by platelike agariciids, Montastraea cav-ernosa, and Orbicella spp. Upper MCEs (water depths of

~30 to 50 m) in the Caribbean, especially in low-gradient shelf settings such as the outer PR-VI Platform, can be domi-nated by Orbicella franksi with a flattened morphology (Weinstein et al. 2016), which presumably represents an important component of the underlying framework. The Orbicella annularis species complex and M. cavernosa have been identified as dominant components of coral cover down to depths of ~40 to 50 m at the Flower Garden Banks in the Gulf of Mexico (Schmahl et al. 2008; Johnston et al. 2013), as well as the reef slopes of Jamaica (Goreau and Goreau 1973; Goreau and Land 1974) and Belize (James and Ginsburg 1979). M. cavernosa can extend to much greater depths, typically developing a flattened, platelike morphology (Goreau and Goreau 1973; Goreau and Land 1974; James and Ginsburg 1979; Lesser et al. 2009, 2010). However, its predominance in terms of coral cover and frame building decreases markedly beyond depths of ~50 m, where platelike agariciids (Agaricia spp..) are the dominant coral cover in both platform and slope settings (Hine et al. 2008; García-Sais 2010; Sherman et al. 2010, 2016). Agaricia lamarcki, A. fragilis, A. grahamae?, and A. agaricites/humilis dominate at depths of 50–60 m. In deeper settings, A. undata is over-whelmingly the dominant coral cover. Vertical exposures on some slopes in Puerto Rico suggest that these platelike corals are also an important component of underlying framework (Fig. 44.11).

Encrusters and secondary frame builders, such as coral-line algae, are also important components of mesophotic benthic cover and framework. For example, on the insular slope of southwest Puerto Rico at depths of ~50 to 70 m, coral cover averages ~10 to 13%, while cover of coralline algae and calcareous members of the family Peyssonneliaceae averages ~18% (Sherman et al. 2010). Similarly, at Pulley Ridge on the southern end of the west Florida Shelf at depths of 60–75 m, benthic cover is dominated by coralline algae at ~31% followed by coral at 11% (Hine et al. 2008). Subsequent surveys on Pulley Ridge have documented a marked decrease in coral cover over time (Reed et al. 2017). The combination of coralline algae and plate corals results in a foliate or shin-gled framework. Examination of lithic substrates collected by divers along the southern margin of the PR-VI Platform at depths of 50–90 m showed scleractinian corals and coralline algae to be the primary framework components. However, well-lithified microcrystalline carbonate (micrite) of possi-ble autochthonous/microbial origin was also common and may be an important component of mesophotic frameworks (Hutchinson and Sherman 2013). Along low- gradient slopes and platforms in the Caribbean accumulations of algal nod-ules (rhodoliths) are common and form an important hard substrate for sessile benthos (Fig. 44.7; Macintyre et al. 1991; Locker et al. 2010; Sherman and Appeldoorn 2015). These nodules are actively forming at mesophotic depths and


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represent an important structural aspect of MCEs (Reid and Macintyre 1988; Prager and Ginsburg 1989).

Coring of submerged reefs around Tahiti at depths rang-ing from ~40 to 120 m by IODP Expedition 310 (Camoin et al. 2007) provided insight on possible mesophotic frame-work and accretion. The cores consist primarily of shallow-water (<10–15 m) coral-algal assemblages that accreted upward from ~16 to ~8 ka associated with rising sea level during the last deglaciation. In all cases, cores are capped by a deep- water (>20–30 m) assemblage prior to reef drowning and the end of vertical accretion (Abbey et al. 2011b). The deep- water coral assemblage is dominated by encrusting forms, including Montipora tuberculosa, Pachyseris speci-osa, Leptoseris solida, and Pavona varians (Fig. 44.12). The deep-water algal assemblage is characterized by Mesophyllum funafutiense, Lithoporella melobesioides, and Hydrolithon breviclavium encrusting or intergrown with laminar corals (Fig. 44.12). The deep-water assemblages capping the cores are up to 9 m thick and may represent a record of mesophotic accretion. However, radiocarbon ages of corals and coralline algae from these intervals range from ~5.9 to 11.2 ka, sug-gesting that these intervals represent the transition to meso-

photic depths and eventual reef drowning rather than recent accretion at mesophotic depths. In many cases, the deep-water assemblages are, in turn, capped by an interval of coral-algal fragments and microbialites, which may provide a better representation of true mesophotic framework and accretion at these sites. Camoin et al. (2006) and Seard et al. (2011) refer to these as “slope microbialites,” which they associate with the ultimate stage of a biological succession indicating a deepening environment and drowning of shal-low-water coral-algal communities.

Where MCEs have been studied on the outer shelf of the GBR, Australia, mesophotic coral growth is concentrated on submerged ridges and pinnacles. Planar tops of submerged ridges hold the highest diversity of mesophotic corals and coral growth forms including branching species of Acropora, Pocillopora, and Seriatopora. The steep sides of these fea-tures have a lower diversity assemblage of flat, plate, and encrusting forms such as Echinophyllia and Leptoseris (Bridge et al. 2011a). At depths <60 m framework is com-posed primarily of massive, tabular, and laminar colonies of Porites, Montipora, Pachyseris, and merulinids along with crustose coralline algae including lithophylloids and minor

Fig. 44.11 Buildup of plate corals, primarily Agaricia spp., on steep slope off southwest Puerto Rico, ~62 msw. (From Sherman et al. 2010; Photo credit: H. Ruíz)


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mastophoroids. Beyond 60 m, framework is characterized by much thinner (<2 cm), plate, and encrusting coral morpholo-gies including Porites, Montipora, Pachyseris, and Leptoseris associated with melobesioids and Sporolithon (Bridge et al. 2012b; Abbey et al. 2013)

MCEs of the Hawaiian Islands are divided into three gen-eral categories (Rooney et al. 2010). Upper MCEs are found at depths of 30–50 m and dominated by corals found at shal-low reefs but with lower diversity. Important corals include Pocillopora meandrina, P. damicornis, Montipora capitata, and Porites lobata. Branching/plate coral MCEs are found at depths of 50–80 m. Some of these reefs are dominated by low-relief branching corals up to 30 cm high that have been tentatively identified as a species of Montipora or Anacropora (Rooney et al. 2010). Other reefs in this depth range are dominated by M. capitata with a platelike morphology.

Leptoseris MCEs are the dominant reef type found at depths from ~80 m to at least 130 m. Corals are typically large thin-walled colonies with platelike to foliaceous morphologies.

44.5.2 Mesophotic Coral Growth and Framework Accretion

Very few studies have directly assessed growth and calcifica-tion rates of important mesophotic frame builders or net mesophotic reef accretion (but see Watanabe et al. 2019). Grigg (2006) determined growth rates of Porites lobata in the ‘Au‘au Channel, Hawaiʻi, at depths from 3 to 50 m. Optimal growth rates of 13.5 mm year−1 occurred at 6 m water depth with a roughly exponential decline in growth rate with depth to 3.0 mm year−1 at 50 m. Additionally, there

Fig. 44.12 Coral reef limestone recovered from submerged reefs around Tahiti by IODP Expedition 310. (a) Mesophotic coral assemblage domi-nated by Pachyseris speciosa, Pavona varians (1), and Montipora (2). (b) Mesophotic algal assemblage showing Mesophyllum funafutiense (1) forming frameworks of foliose plants. (Adapted from Abbey et al. 2011b)


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is a corresponding decline in both colony size and abundance with depth. Based on the measured growth rates along with estimates of bioerosion, a depth limit of reef accretion at this locale of ~50 m was proposed. This was supported by radio-metric ages of lithic substrates that showed a sharp increase in age from essentially modern at depths <50 m to 8–9 ka at depths >50 m (Grigg 2006). More recently, Watanabe et al. (2019) compared growth rates of massive Porites between shallow and mesophotic depths in the Red Sea (5 and 50 m) and Okinawa, Japan (4 and 40 m). This study also reports decreased growth rates at mesophotic depths but also geo-graphical variation among regions.

On the basis of radiometric dating and paleoenvironmen-tal analyses of dredge samples, Abbey et al. (2013) identified two episodes of deglacial mesophotic accretion on the GBR. The first occurred from 13 to 10 ka on the outer shelf at modern water depths of 100–130 m, with framework displaying a clear deepening upward succession. Initial accretion consisted of a massive and tabular coral-algal assemblage (paleowater depth <60 m) succeeded by a plate and encrusting coral-algal assemblage (paleowater depth <80–100 m) and finally by a non-coral encruster assemblage (paleowater depth >100 m) indicative of drowning and the end of active accretion. The second phase of mesophotic accretion occurs from 8 ka to present with plate and encrust-ing coral-algal framework forming at depths of 80–100 m and massive and tabular coral-algal framework forming at depths of 45–60 m (Abbey et al. 2013). The hiatus in meso-photic accretion is thought to be related to a shelf- wide influx of siliciclastic sediments associated with rising sea levels and remobilization of shelf sediments (Abbey et al. 2013). The broad range in ages of samples dredged from modern mesophotic depths of ~50 to 100 m suggests that mesophotic accretion at these sites is both slow and patchy.

Weinstein et al. (2016) determined average linear exten-sion rates of corals collected from reefs on the outer PR-VI Platform at depths of 30–45 m that ranged from ~0.7 to 0.9 mm year−1, which are at least an order of magnitude lower than rates calculated for the same species complex at shallower depths in Puerto Rico and the US Virgin Islands (Hubbard and Scaturo 1985; Torres and Morelock 2002). This sharp decline in extension rates is primarily attributed to decreasing irradiance with depth (Hubbard and Scaturo 1985; Bosscher and Meesters 1993; Lesser et al. 2010). Using the linear extension rates along with calculations of secondary accretion and loss of material due to macroboring, Weinstein et al. (2016) further determined net framework accretion, which ranged from ~1.2 to 1.5 kg m−2 year−1. Applying a carbonate budget approach with multiple assumptions, the US Virgin Islands MCEs were estimated to have the potential to vertically accrete ~1 to 4 m in 6 ka, the minimum amount of time these reefs have likely been at mesophotic depths (Weinstein 2014). Collection and analysis

of MCE cores are greatly needed to better determine modern and past MCE reef accretion potential.

44.6 Sediments and Sedimentary Dynamics

44.6.1 Composition and Texture of MCE Sediments

Sediments in reef settings are largely autochthonous and derived primarily from the breakdown and decomposition of reef framework and other calcareous reef dwellers along with, to a lesser degree, calcareous material produced by physiochemical precipitation (Scoffin 1987; Tucker and Wright 1990; Perry 2007). Where reefs develop close to shore or sources of fluvial sediment discharge, external inputs of allochthonous (terrigenous) sediments can be important (Scoffin 1987; Tucker and Wright 1990; Perry 2007). MCE sediments are primarily composed of skeletal sands and gravels with trace amounts of mud (Scoffin and Tudhope 1985; Boss and Liddell 1987; Weinstein et al. 2015b). Important skeletal grain types include coral, calcare-ous green algae (primarily Halimeda), benthic foraminifera, coralline algae, mollusks, and micritic grains (Fig. 44.13). Abundances of various skeletal constituents are largely reflective of adjacent benthic cover (Scoffin and Tudhope 1985; Boss and Liddell 1987; Weinstein et al. 2015b). Statistical analysis of sediment constituent data has demon-strated correlations between skeletal grain types and benthic cover and allowed for identification of distinct sedimentary biofacies corresponding to different reef or shelf zones (Scoffin and Tudhope 1985; Boss and Liddell 1987; Weinstein et al. 2015b). Abundance of coral grains is high only close to reefs and other rocky substrates. Halimeda and benthic foraminiferal sands dominate interreef areas and may cover the bulk of MCE habitats (Scoffin and Tudhope 1985; Boss and Liddell 1987). On marginal reef slopes, there is often a marked increase in relative abundance of Halimeda grains, and corresponding decrease in coral, with depth (Moore et al. 1976; James and Ginsburg 1979; Hoskin et al. 1986; Boss and Liddell 1987). Halimeda sands and gravels have also been found to form a discernable band between 60 and 100 m depths on the outer GBR shelf (Scoffin and Tudhope 1985).

44.6.2 Sedimentary Dynamics

Sediment dynamics exert a fundamental control on the char-acter and distribution of both shallow shelf reefs and deeper MCEs (Goreau and Land 1974; James and Ginsburg 1979; Hubbard 1986; Liddell and Ohlhorst 1988;


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Liddell et al. 1997; Perry 2007; Bridge et al. 2011a). Although MCEs on broad, passive-margin shelves may be sufficiently removed from deleterious effects of terrestrial inputs, on narrower, active, and insular margins, influx of ter-rigenous sediments can exert a considerable influence even at mesophotic depths (e.g., Appeldoorn et al. 2016). The depth of MCEs generally removes them from resuspension of bottom sediments due to wave activity (Baker et al. 2016a; Weinstein et al. 2015b), which plays an important role in shallow reef systems (Storlazzi et al. 2004; Ogston et al. 2004; Hernandez et al. 2009; Sherman et al. 2013b). However, reduced wave energy at mesophotic depths can also lead to more sediment accumulation (rather than flushing) limiting coral growth in some settings, particularly in MCEs closer to shore and terrigenous inputs (Appeldoorn et al. 2016; Bridge 2016). Collectively, their depth and distance from shore would suggest that vertical fluxes of sediment to the seafloor in MCEs should be relatively low compared to shallow reefs. This is supported by sediment trap measurements made at MCEs on the insular slope of southwest Puerto Rico, where trap accumulation rates of

suspended sediment were an order of magnitude lower than those recorded at adjacent shallow shelf reefs (Sherman et al. 2016).

Although Weinstein et al. (2015b) found that the shelf MCEs on the outer PR-VI Platform experience limited sediment transport or influx of allochthonous materials, studies of the GBR and Gulf of Carpentaria shelves of Australia found these are very dynamic settings (Larcombe and Carter 2004; Harris and Heap 2009). On the GBR outer shelf in water depths of 40–80 m, fair-weather sediment transport is driven by tidal and other unidirectional currents that are strong enough to form small dunes in biogenic sand (Larcombe and Carter 2004). Tidal current transport results in the disintegration of soft carbonate sediments, creating spatially constrained, detrital carbonate mud deposits on the southern GBR shelf and in Torres Strait (Harris 1994). Additionally, the high percentage of relict grains in interreef sediments of the outer shelf was cited as evidence for frequent storm-associated erosion of the seafloor and reworking of sediment (Larcombe and Carter 2004). Harris and Heap (2009) described Holocene-age talus deposits

Fig. 44.13 Thin section of epoxy-embedded surface reef sediment collected on a 45 m deep upper MCE south of St. Thomas in the US Virgin Islands. Coral (c) was the most abundant (37.25%) grain type, by surface area, in this image when 50 random points were used to identify grain composition. Some other grain type components interpreted under random points included foraminifera (f), Halimeda sp. (h), red coralline algae (r), and mollusks (m). All grain types, including those identified in the figure, may have experienced various stages of micritization, but most are still identifiable based on original structure. Methods for identification, analysis and collection, and additional data provided by Weinstein et al. (2015b)


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along the leeward slopes of submerged banks in the Gulf of Carpentaria, northern Australia. Based on their age and orientation, they concluded that the talus deposits were formed by cyclone-induced currents eroding sediment from bank tops and depositing it on the leeward sides of the banks (Harris and Heap 2009). Cyclones and associated sediment transport may be limiting modern mesophotic reef growth in this region (Harris 2016).

Mesophotic slope settings, especially those associated with active and insular margins, are similarly very dynamic sedimentary environments where downslope bed-load transport exerts a fundamental influence on MCEs (Goreau and Land 1974; Colin et al. 1986; Liddell and Ohlhorst 1988; Liddell et al. 1997; Sherman et al. 2010, 2016). In slope settings, copious sediment is generated at the shelf edge by the physical and biological breakdown of reef framework and decomposition of other calcareous reef dwellers (Hoskin et al. 1986; Baker et al. 2016b). This sediment is subsequently transported downslope as bed load (Colin et al. 1986; Hoskin et al. 1986; Hubbard 1986; Hubbard et al. 1990; Baker et al. 2016b; Colin 2016; Sherman et al. 2016) or, more rarely, in suspension as a near-bed density/turbidity flow (Goreau and Land 1974; Moore et al. 1976). Sherman et al. (2016) demonstrated that rates of downslope bed-load transport are orders of magnitude higher than vertical fluxes of sediment to the seafloor and highly variable, by orders of magnitude, both spatially and temporally. While sediment transport during tropical cyclones far exceeds that during fair-weather conditions and plays a major role in the long-term sediment budget of tropical reef systems (e.g., Hubbard 1992), continuous off-shelf sediment transport occurs even during non-storm conditions (Hubbard et al. 1990; Hughes 1999; Morgan and Kench 2014; Sherman et al. 2016) and, thus, can continuously influence insular-slope MCEs. Hubbard (1992) demonstrated that the tremendous flushing of sediment from the insular shelf on the north coast of St. Croix, US Virgin Islands, during the passage of Hurricane Hugo (1989) was associated with offshore currents generated by the decay of wave setup and storm surge with the passing of the storm. Important drivers of sediment transport in MCEs during fair- weather conditions are less obvious. Given the steep gradient of slope environments, slow downslope creep and gravity slumping are likely important (Goreau and Land 1974; Moore et al. 1976). On the basis of correlations between peaks in sediment trap accumulation rates and SWAN- modeled wave-orbital velocities, Sherman et al. (2016) suggested that surface waves may influence sediment dynamics even in mesophotic settings. However, other driving mechanisms, such as tidal currents or internal waves, may also be important. Additional studies that include contemporaneous monitoring of hydrodynamics and sedimentary response are required to more conclusively identify important drivers of sediment transport in meso-photic settings.

44.7 Cementation and Lithification

Submarine cementation and lithification are key processes in reef systems that are partly responsible for the steep, wave- resistant profiles of reefs and carbonate margins (Tucker and Wright 1990). Cementation is thought to occur predominantly in high wave-energy areas on the seaward margins of reefs where water can be flushed through the porous structure of the framework (Macintyre 1977; Macintyre and Marshall 1988). However, there is abundant evidence for syndepositional cementation and lithification occurring at mesophotic depths as well, such as on the deep fore-reef of Jamaica (Land and Goreau 1970; Goreau and Land 1974), deep reef front of Belize (James and Ginsburg 1979; Grammer et al. 1993), the Bahamas (Grammer et al. 1993), and carbonate mounds in the eastern Gulf of Mexico (Locker et al. 2016). Combined with experimental evidence of syndepositional cementation (Grammer et al. 1999; Weinstein et al. 2015a), it is now believed that rapid (a few years) carbonate marine lithification is not always influenced by strong currents and waves or restricted to shallower reef habitats (Grammer et al. 1999; Weinstein et al. 2015a). Grammer et al. (1999) suggested cementation is not surprising at mesophotic depths because similar conditions of calcium carbonate supersaturation and warm temperatures needed for cementation (Tucker and Wright 1990) are common at mesophotic depths in tropical settings.

Reef cements are composed of aragonite and magnesian (Mg) calcite with a variety of morphologies. Mg calcite is more common and can occur as microcrystalline rinds, peloids, equant crystals and bladed spar. Aragonite cement occurs as acicular arrays, commonly as syntaxial overgrowths on aragonitic substrates, such as corals, as well as botryoidal splays (James and Ginsburg 1979; Macintyre and Marshall 1988; Tucker and Wright 1990). Weinstein et al. (2015a) found fibrous aragonite needles as the most common cement type to coat and bind experimentally deployed Bahamian ooids in the US Virgin Islands (Fig. 44.14), but found no major difference between mesophotic and shallower sites or between samples suspended above or upon the seafloor. Alternatively, Land and Goreau (1970) found the major cements responsible for reef lithification, including at mesophotic depths, were Mg calcite occurring as either a drusy, isopachous fringe of scalenohedral crystals or a laminated or massive pelleted micrite. Additionally, experimental deployments of carbonate substrates in mesophotic settings have demonstrated rapid syndepositional cementation (Grammer et al. 1999; Weinstein et al. 2015a). These studies suggest the likelihood for high preservation potential of original sediment textural features, the formation of seismically resolvable hardgrounds at mesophotic depths (Grammer et al. 1999), and a mechanism for stabilizing steep carbonate slopes at least at the angle of repose (Grammer et al. 1993). Marine cements have also been detected on the


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GBR in some of the few major cores taken at mesophotic depths, although these likely represent shallower depths based on lithology and indicators of subaerial exposures (Yokoyama et al. 2011).

In addition to providing hard lithic substrates for coloni-zation by sessile benthos, marine cementation and lithifica-tion are important for reinforcing reef framework, thus aiding carbonate accretion. For example, lithification of reefal material within 1 m of the reef-water interface has been directly observed in Jamaica down to 70 m on a massive scale, leading to the preservation of large (>1 m) carbonate deposits (Land and Goreau 1970), presumably all of MCE origin. Well-lithified reef limestones of postglacial age have also been documented throughout mesophotic depths on the marginal reefs of Jamaica (Goreau and Land 1974) and Belize (James and Ginsburg 1979). Despite observations of syndepositional cement and modern lithified reef material, there is still a large void in documenting distribution, amount, and type of marine cements in MCEs, their structural impact, and general comparisons to shallower habitats. This is espe-cially true beyond the Caribbean and represents a future research priority.

44.8 MCEs in the Geologic Record

The majority of research on MCEs has focused on Quaternary deposits, especially modern settings with living coral cover. However, discoveries of biostromes and bioherms specifi-cally interpreted as forming in mesophotic conditions (e.g., Morsilli et al. 2012; Novak et al. 2013; Shao et al. 2017; Zapalski et al. 2017) imply that MCEs likely have a robust geological history. However, determining absolute meso-photic depths in the fossil record is difficult. The most com-mon method for interpreting fossil deposits as mesophotic

has been the identification of abundant coral with plate mor-phologies. Plate corals are found throughout the scleractin-ian fossil record, often interpreted to reside in calm, deep paleoenvironments with a morphology that has been sug-gested as indicative of photosymbiosis (Rosen et al. 2000). Massive coral species often flatten with depth (Kühlmann 1983; Lesser et al. 2010) to maximize the capture of light (Kahng et al. 2010), and corals with a platelike morphology require significantly less surface light than coral with other morphologies (Hallock and Schlager 1986). However, cau-tion is required when using the abundance of plate coral for interpreting reefs as mesophotic. Low-light conditions pro-duced by high turbidity and/or sedimentation may also facili-tate the growth and deposition of coral with platelike morphology at shallower depths (e.g., Cortés and Risk 1985; Kleypas 1996; Browne 2012). Other indicators, such as com-position of surrounding sediment, makeup of encrusting and associated organisms (such as coralline algae and benthic foraminifera), and geochemical signatures, can aid in solidi-fying mesophotic interpretations.

Even prior to the evolution of the Scleractinia, other coral orders likely formed mesophotic reefs. With an age of approximately 390 Ma, the oldest deposit currently inter-preted as an MCE is found in the Holy Cross Mountains of Poland (Zapalski et al. 2017). These Devonian reefs likely had relatively low relief and accumulation potential. Based on platelike morphologies, Zapalski et al. (2017) also sug-gested the possibility of similar mesophotic interpretations for other Paleozoic deposits in Belgium (Poty and Chevalier 2007) and North America (Stumm 1964), but acknowledged additional study is needed to confirm this interpretation. When considering the ancestors of modern coral reef build-ers, the first fossil record of aragonitic Scleractinia comes from the Middle Triassic (Stanley 1988), although their evo-lutionary origin was likely from the Paleozoic (Stolarski

Fig. 44.14 Scanning electron micrographs of aragonite fibrous cement that formed on smooth Bahamian ooids after 641 days of exposure (1 m above the seafloor) at a US Virgin Islands MCE, 45 m deep (Weinstein et al. 2015a). (a) Evidence of syndepositional cementation binding sediment at mesophotic depths. Orange box indicates location for (b) close-up of inter-fingering aragonite needles binding the grains


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et al. 2011). Interpreted to inhabit soft substrate in protected or deeper settings potentially similar to modern mesophotic depths, early scleractinians consisted of small colonies that lacked reef-building potential until the Late Triassic (Stanley 1988). Mesophotic corals seem to have accumulated sub-stantial (>1 m thick) deposits shortly after. For example, large (>5 m) Upper Jurassic platelike reef deposits with little significant relief, but large lateral extent, are found through-out Europe (Insalaco 1996). The plate corals in these depos-its had low calcification rates (low growth rate and density) and resembled growth forms of modern mesophotic corals, such as Leptoseris. Insalaco (1996) interpreted these reefs as existing below wave base in low energy, high eutrophic areas that usually experienced low sedimentation at depths of 20–80 m.

Mesophotic conditions have also been interpreted for multiple coral bioherm and biostrome deposits from much of the Paleogene and Neogene. Following the K/Pg boundary, corals produced 5–10 m thick bioherm Paleocene deposits in the western Pyrenees and were suggested to have thrived in meso-oligophotic conditions (Pomar et al. 2017). Morsilli et al. (2012) interpreted biostromal layers up to 2 m in thickness and interbedded with clay in a Late Eocene mixed carbonate-siliciclastic southern Pyrenees system as mesophotic in origin. These corals, which resided in areas with limited hydrological activity, progressively produced carbonate lobe buildups but did not form wave-resistant, rigid structures (Morsilli et al. 2012). Nearby, small (~2 m thick) Eocene coral biostrome facies interbedded between nummulitic (a large benthic foraminifera) banks in the South Central Pyrenean Zone were interpreted to be in situ accumulations in a “relatively deep (low light)” environment below storm base (Mateu-Vicens et al. 2012). Another Eocene deposit in Northern Italy consists of two plate coral facies interpreted as growing in “deep” water (Bosellini 1998). In Iran, sedimentological analysis from the Oligocene- Miocene Zagros Basin indicated that some zooxanthellae corals may have formed at mesophotic depths, but there was little reef-building capacity (Dill et al. 2012). More recently in the geologic record, thin-plate Miocene corals, related to various extant zooxanthellate representatives, were deposited in a muddy matrix at least 3 m thick and interpreted to form a patch reef in a turbid mesophotic environment within a prodelta (Novak et al. 2013). As the study of modern MCEs continues to expand, especially from a geological perspective, more sedimentary deposits will likely be discovered or reinterpreted as representing mesophotic settings. Future analysis of fossil mesophotic reef deposits will allow for a better understanding of the evolution of modern MCEs and coral in general, how MCEs responded to changing environmental conditions, and if they may have served as a refugia in the past.

44.9 Discussion and Conclusions

Geomorphology exerts a fundamental control on the occur-rence, distribution, and composition of MCEs by providing hard substrates suitable for colonization by corals and other sessile benthos, as well as influencing and directing the transport and/or accumulation of sediment. On broad shelves that that dip gently into mesophotic depths before reaching the shelf break, MCEs occur on the shelf and are typically concentrated and best developed on positive relief features that are elevated above the deleterious effects of sediment accumulation (Jarrett et al. 2005; Locker et al. 2010, 2016; Smith et al. 2010, 2016; Abbey et al. 2011a; Bridge et al. 2011a, 2012a; Harris et al. 2013; Weinstein et al. 2014). Where shelf breaks occur at shallower depths, mesophotic habits occur largely on marginal slopes (Goreau and Land 1974; James and Ginsburg 1979; Liddell and Ohlhorst 1988; Ginsburg et al. 1991; Liddell et al. 1997). In these settings, MCE development is favored on steep irregular slopes, where coral cover is concentrated on steep- sided buttresses and sediment is channelized into narrow intervening chutes (Liddell and Ohlhorst 1988; Liddell et al. 1997; Sherman et al. 2010, 2016). In addition to the general geomorphic set-ting, such as shelf, slope, or isolated bank, important geo-morphic factors include proximity to adjacent terrestrial or marine sediment sources, degree of exposure to prevailing seas and storms, seafloor gradient, seafloor roughness/rugos-ity (on multiple scales), and substrate type, such as coral-algal “reef,” hardground, sand, and rubble (Sherman et al. 2010; Bridge et al. 2011a). Together these factors can deter-mine the suitability of a site for the development of MCEs and, therefore, can serve as criteria for the identification of potential MCEs.

Quaternary sea-level fluctuations have played a key role in shaping the antecedent topography upon which many MCEs are built (Macintyre et al. 1991; Jarrett et al. 2005; Beaman et al. 2008; Abbey et al. 2011a; Locker et al. 2016). Along insular and continental margins, common features such as relict reefs, submarine terraces, paleoshoreline structures, and pronounced breaks in slope are reflective of past sea-level positions and represent prime locations for MCE development. Relict reefs are largely constructional (i.e., accretionary) features and provide rocky substrates elevated above the surrounding seafloor and effects of sediment accumulation. Paleoshoreline structures and submarine terraces can be formed by erosional or depositional processes or a combination thereof. They similarly provide hard substrates, as well as pronounced breaks in slope gradient that facilitate sediment removal. Some of these features formed during the last deglaciation at times of relatively slower sea-level rise and then subsequently drowned during episodes of rapid rise associated with glacial


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meltwater pulses (Fairbanks 1989; Macintyre et al. 1991; Locker et al. 1996; Macintyre 2007). However, other features may have a more complex origin related to multiple episodes of slowly rising sea level over longer Quaternary timescales (Abbey et al. 2011a). Coring and dating of submarine ter-races off the island of Oʻahu, Hawaiʻi have shown these to be complex structures formed over multiple interglacial inter-vals (Sherman et al. 1999, 2014; Fletcher et al. 2008). A con-sideration of eustatic sea-level history combined with local vertical offsets associated with tectonic or isostatic move-ments can be a key guide for locating MCE topography at predictable depths and identifying important targets for future exploration and research.

Seafloor gradient and roughness can affect irradiance and sedimentary dynamics on MCEs (Sherman et al. 2010; Bridge et al. 2011a). Although shelves represent the largest areas that may potentially support MCEs, MCEs in shelf settings are generally restricted to submerged ridges and pinnacles built upon outer shelves. Thus, the true area of MCE occurrence is much less than the total area of the shelf at mesophotic depths. Low-gradient seafloor receives higher levels of irradiance than steep slopes. In MCEs where irradiance is already reduced by depth, subtle changes in seafloor gradient may be sufficient to affect community composition (Bridge et al. 2011a). Although low-gradient seafloor provides higher levels of irradiance conducive to MCE development, it also has an increased potential for accumulation of sediments detrimental to MCE development. Therefore, low-gradient seafloor will support MCEs where it is far removed from sediment sources or where it occurs on topographic highs elevated above the surrounding seafloor and the influence of sediment accumulation and abrasion. Examples of such settings include the outer PR-VI Platform south of the US Virgin Islands (Smith et al. 2010, 2016; Weinstein et al. 2014) and planar tops of submerged reefs on the outer GBR shelf (Bridge et al. 2011a, b). These relatively horizontal habitats can support well-developed MCEs with high coral cover and a high diversity of mesophotic corals and coral growth forms including branching and massive species. However, these settings are typically restricted to depths less than 50–60 m. At greater depths, horizontal habitats are generally typified by a low-relief, low-rugosity rubbly substrate with patchy occurrences of plate corals (Hine et al. 2008; García-Sais 2010; Sherman et al. 2010, 2016; Bridge et al. 2011a).

Marginal slopes are prime habitats for MCEs but present challenges to coral growth in terms of reduced availability of light and persistent downslope transport of sediment. Although low-gradient slopes provide higher levels of irradiance, decreased slope gradient and rugosity lead to sediment transported downslope being spread over a broader area, such as a sheet flow. This results in higher sand cover limiting recruitment and abundance of corals and other

sessile megabenthos. On steep, irregular slopes, downslope sediment transport is more channelized into narrow sand chutes, and mesophotic coral cover is typically higher on steep slopes (versus low-gradient slopes) where it is concentrated on steep-sided buttresses and other topographic highs. In these steep habitats, corals are predominantly flat, plate, and encrusting forms. In wall habitats, irradiance levels are greatly reduced limiting coral growth and MCE development (Liddell and Ohlhorst 1988; Liddell et al. 1997). Although ledges and other low-angle surfaces on walls provide increased irradiance, they are subject to burial by sediments offsetting the advantages of increased irradiance for coral growth. A deep escarpment dropping precipitously from depths of 55–65 m to depths of 120–160 m or more is a common feature along many marginal slopes in the Caribbean (Goreau and Land 1974; James and Ginsburg 1979; Sherman et al. 2010) and can mark the local limit of vigorous mesophotic coral growth (Liddell and Ohlhorst 1988; Liddell et al. 1997; Sherman et al. 2010).

While styles and rates of accretion of shallow reefs are well documented over the Holocene (e.g., Hubbard et al. 1997, 2005, 2008, 2013; Montaggioni 2005; Montaggioni and Braithwaite 2009), we lack an equivalent understanding of MCEs. Assessments of calcareous benthic cover in MCEs provide an indication of underlying framework. However, it is unclear to what degree these communities are actively accreting or represent just a thin veneer over relict substrates. In most cases, evidence supports the latter scenario. Thus, while shallow reefs have built significant topographic features during the Holocene (Montaggioni 2005; Hubbard et al. 2008, 2013; Montaggioni and Braithwaite 2009), MCEs have largely conformed to antecedent topography. Put another way, rather than generate topography, MCEs are dependent upon it.

For example, MCEs in the Gulf of Mexico are closely associated with relict features, such as Pulley Ridge in the southeast Gulf of Mexico, which is thought to be a sub-merged barrier island complex (Fig. 44.3). Because underly-ing barrier island geomorphology (e.g., beach ridges, recurved spits, and relict inlets) is readily discernable in mul-tibeam imagery, it is unlikely that there has been much meso-photic accretion, which over time would obscure the relict topography. Rather, recent MCE accretion is likely very thin (<1–2 m) forming a biostromal veneer that conforms to the underlying topography (Jarrett et al. 2005; Hine et al. 2008). Ages of dredge samples from MCE habitats on the GBR at depths of ~50 to 100 m range from ~0 to 12 ka indicating that mesophotic accretion is slow and patchy, both spatially and temporally (Abbey et al. 2013). Grigg (2006) similarly found that ages of lithic substrates in Hawaiʻi increased dramati-cally at depths >50 m, suggesting limited recent mesophotic accretion.


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Coring of reef structures at mesophotic depths has been attempted at only few locales including Barbados (Fairbanks 1989), Tahiti (Camoin et al. 2007), and Australia’s GBR (Yokoyama et al. 2011), Gulf of Carpentaria (Harris et al. 2008), and Lord Howe Island (Woodroffe et al. 2010). Results from these studies indicate that the features cored are largely relict and composed of shallow-water coral-algal assemblages formed during the last deglaciation between about 6 and 20 ka. These studies were focused on identifying and radiometrically dating the shallow-water assemblages to document sea-level change and reef response over the last deglaciation. Cores often display deepening upward succes-sions. Deep-water coral-algal communities with interpreted paleowater depths of >20–30 m at the tops of some of the Tahiti cores may represent a record of mesophotic reef accre-tion (Abbey et al. 2011b). However, radiocarbon ages from these intervals range from ~5.9 to 11.2 ka. Thus, modern mesophotic accretion is not documented, and it remains unclear whether these deep-water communities represent the drowning and “death” of the reefs or if accretion is still occurring. Additional work focused on the uppermost sec-tions of cores from these efforts could yield key information on the structure and accretion of mesophotic framework. Additional coring studies targeting mesophotic features at other locales would similarly provide information on MCE development and their response to changes in sea level and other environmental parameters, as well as important records of late Quaternary oceanographic, climatic, and eco-logic change.

Based on changes in growth rate with depth of the frame- building coral Porites lobata, Grigg (2006) proposed a depth threshold of ~50 m as a limit for reef accretion in Hawaiʻi. However, this has not been tested in other settings. Weinstein et al. (2016) determined linear extension rates of Orbicella franksi from upper mesophotic reefs on the PR-VI-Platform at depths of 30–45 m, which were notably lower than rates calculated for the same species complex at shallower depths by other studies. They further were able to estimate net framework accretion at these sites. This study provides key information, and similar studies assessing additional frame builders over a broader depth and geographic range are needed. For example, O. franksi becomes rare beyond depths of ~50 m, where Agaricia spp. become the overwhelmingly dominant component of mesophotic coral cover. Additionally, the role of autochthonous micrite/microbialites in mesophotic framework needs to be assessed. Microbialites have been described as major structural and volumetric components of reef sequences in some locales, particularly on deep fore- reef slopes, where they are associated with a deepening environment and drowning of shallow-water coral-algal communities (Cabioch et al. 2006; Camoin et al. 2006; Seard et al. 2011). In an assessment of reef accretion data from across the Caribbean, Hubbard et al. (2008) found Holocene

accretion rates of shallow reefs (water depths 0–25 m) averaged ~3 m ky−1 with little, if any, relationship to water depth or coral type. If current indications regarding mesophotic accretion are correct, there is apparently an abrupt decline in accretion at depths of ~30 to 50 m that should be assessed. This has a bearing on the ability of MCEs to generate their own structural complexity, as well as their role in the construction of carbonate margins.

Sedimentation and sedimentary dynamics are known to profoundly influence both shallow and mesophotic coral ecosystems (Hubbard 1986; Rogers 1990; Sherman et al. 2010, 2016; Bridge et al. 2011a). Sediments can affect corals and other sessile benthos by burial, abrasion, and increased turbidity. Proximity to adjacent sediment sources (terrestrial or marine) provides an indication of the potential impacts of sediment and sedimentary dynamics on MCEs. Typically, the further removed an MCE is from sediment sources, the more likely it is to support high abundance of sessile megabenthos. MCEs can exist in close proximity to sediment sources, provided that other factors, such as sand chutes on steep slopes, allow for effective transport of sediments through the system without significant deleterious effects, such as the MCEs on the steep slope of northwestern St. Croix (Smith and Holstein 2016). Sediments in MCEs are dominantly autochthonous skeletal sands and gravels with grains consisting primarily, in varying relative abundances, of coral, coralline algae, calcareous green algae (primarily Halimeda), forams, and mollusks (Scoffin and Tudhope 1985; Hoskin et al. 1986; Boss and Liddell 1987; Weinstein et al. 2015b). Relative abundances of different skeletal grain types typically reflect the makeup of adjacent benthic cover. A relative increase in the abundance of Halimeda grains is commonly found in mesophotic settings (Moore et al. 1976; James and Ginsburg 1979; Scoffin and Tudhope 1985; Hoskin et al. 1986; Boss and Liddell 1987).

With notable exceptions, such as the highly impacted MCEs off Ponce, Puerto Rico (Appeldoorn et al. 2016), the depth and typical distance from the shore of most MCEs limit inputs of allochthonous/terrigenous materials, as well as resuspension of in situ sediments due to wave activity (Armstrong et al. 2006; Weinstein et al. 2015b; Sherman et al. 2016). Vertical fluxes of sediments to the seafloor in MCEs are typically low and likely not an important influence in most cases (e.g., Sherman et al. 2016). However, in slope settings, especially on active and insular margins, downslope bed-load transport of sediment can be orders of magnitude higher than vertical fluxes and likely exerts an important influence on MCEs (Sherman et al. 2016). Although off- shelf/downslope movement of sediments has been well documented at several locales (e.g., Hoskin et al. 1986; Hubbard 1986; Hubbard et al. 1990; Hughes 1999; Sherman et al. 2016), identifying important drivers of sediment transport in mesophotic settings remains elusive. Tropical


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cyclones and similar events can trigger large-scale sediment movements and play a major role in the long-term sediment budget of tropical reef systems (e.g., Hubbard 1992). However, in some settings, off-shelf/downslope sediment transport is a chronic process and occurs even during non- storm conditions (Hubbard et al. 1990; Hughes 1999; Morgan and Kench 2014; Sherman et al. 2016) and thus can continuously influence insular-slope MCEs. Potential drivers of downslope movements include gravitational creep and slumping, surface waves, internal waves, and wind-driven and tidal currents. Additional studies that include contemporaneous monitoring of hydrodynamics and sedimentary response are required to more conclusively identify the relative importance of these different drivers of sediment transport in mesophotic settings. These same drivers could also exert important influences on fluxes of nutrients, (organic) carbon, plankton, and larvae, as well as temperature variations associated with fluctuations in the thermocline. Results of studies of this type would be of broad interest to a wide range of scientists examining the sedimentology, ecology, biogeochemical cycling, and physi-cal oceanography of similar settings.

Acknowledgements CES drew extensively upon knowledge gained from research on MCEs in Puerto Rico and US Virgin Islands that was supported by NOAA/NCCOS awards NA06NOS4780190, NA09NOS4260243, NA10NOS4260223, and NA11NOS4260184 to the UPRM Caribbean Coral Reef Institute. He further wishes to acknowledge Richard Appeldoorn for numerous stimulating discus-sions that helped to refine our concepts and the UPRM-DMS technical diving team including Ivonne Bejarano, Milton Carlo, Doug Kesling, Michael Nemeth, Hector Ruiz and Evan Tuohy. We thank Bret Jarrett for providing images for the Pulley Ridge MCE. We also thank two anonymous reviewers for their critical assessments and helpful suggestions.

References

Abbey E, Webster JM, Beaman RJ (2011a) Geomorphology of sub-merged reefs on the shelf edge of the Great Barrier Reef: the influ-ence of oscillating Pleistocene sea-levels. Mar Geol 288(1–4):61–78

Abbey E, Webster JM, Braga JC, Sugihara K, Wallace C, Iryu Y, Potts D, Done T, Camoin G, Seard C (2011b) Variation in deglacial coralgal assemblages and their paleoenvironmental significance: IODP expedition 310, “Tahiti Sea Level.” Glob Planet Chang 76(1–2):1–15

Abbey E, Webster JM, Braga JC, Jacobsen GE, Thorogood G, Thomas AL, Camoin G, Reimer PJ, Potts DC (2013) Deglacial mesophotic reef demise on the Great Barrier Reef. Palaeogeogr Palaeoclimatol Palaeoecol 392:473–494

Alley RB, Agustsdottir AM (2005) The 8k event: cause and conse-quences of a major Holocene abrupt climate change. Quat Sci Rev 24:1123–1149

Appeldoorn R, Ballantine D, Bejarano I, Carlo M, Nemeth M, Otero E, Pagan F, Ruiz H, Schizas N, Sherman C, Weil E (2016) Mesophotic coral ecosystems under anthropogenic stress: a case study at Ponce, Puerto Rico. Coral Reefs 35(1):63–75

Armstrong RA, Singh H, Torres J, Nemeth RS, Can A, Roman C, Eustice R, Riggs L, Garcia-Moliner G (2006) Characterizing the deep insular shelf coral reef habitat of the Hind Bank Marine Conservation District (US Virgin Islands) using the Seabed autono-mous underwater vehicle. Cont Shelf Res 26(2):194–205

Baker E, Puglise KA, Colin P, Harris PT, Kahng SE, Rooney JJ, Sherman C, Slattery M, Spalding H (2016a) What are mesophotic coral eco-systems? In: Baker EK, Puglise KA, Harris PT (eds) Mesophotic coral ecosystems—a lifeboat for coral reefs? The United Nations Environment Programme and GRID-Arendal, Nairobi, pp 11–19

Baker EK, Puglise KA, Harris PT (eds) (2016b) Mesophotic coral ecosystems—a lifeboat for coral reefs? The United Nations Environment Programme and GRID-Arendal, Nairobi

Banks KW, Riegl BM, Richards VP, Walker BK, Helmle KP, Jordan LKB, Phipps J, Shivji MS, Spieler RE, Dodge RE (2008) The reef tract of continental Southeast Florida (Miami-Dade, Broward and Palm Beach Counties, USA). In: Riegl BM, Dodge RE (eds) Coral reefs of the USA. Springer, Dordrecht, pp 175–220

Bard E, Hamelin B, Fairbanks RG (1990) U-Th ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years. Nature 346:456–458

Bard E, Hamelin B, Arnold M, Montaggioni L, Cabioch G, Faure G, Rougerie F (1996) Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge. Nature 382:241–244

Bard E, Hamelin B, Delanghe-Sabatier D (2010) Deglacial meltwater pulse 1B and Younger Dryas sea levels revisited with boreholes at Tahiti. Science 327(5970):1235–1237

Beaman RJ, Webster JM, Wust RAJ (2008) New evidence for drowned shelf edge reefs in the Great Barrier Reef, Australia. Mar Geol 247(1–2):17–34

Blanchon P, Jones B (1997) Hurricane control on shelf-edge-reef archi-tecture around Grand Cayman. Sedimentology 44:479–506

Blanchon P, Shaw J (1995) Reef drowning during the last deglacia-tion: evidence for catastrophic sea-level rise and ice-sheet collapse. Geology 23(1):4–8

Blanchon P, Jones B, Ford DC (2002) Discovery of a submerged relic reef and shoreline off Grand Cayman: further support for an early Holocene jump in sea level. Sediment Geol 147(3–4):253–270

Bosellini FR (1998) Diversity, composition and structure of Late Eocene shelf-edge coral associations (Nago Limestone, northern Italy). Facies 39(1):203–225

Boss SK, Liddell WD (1987) Patterns of sediment composition of Jamaican fringing reef facies. Sedimentology 34(1):77–87

Bosscher H, Meesters EH (1993) Depth related changes in the growth rate of Montastrea annularis. Proc 7th Int Coral Reef Symp 1:507−512

Brakel WH (1979) Small-scale spatial variation in light available to coral reef benthos: quantum irradiance measurements from a Jamaican Reef. Bull Mar Sci 29(3):406–413

Bridge TCL (2016) Mesophotic coral ecosystems examined—the Great Barrier Reef, Australia. In: Baker EK, Puglise KA, Harris PT (eds) Mesophotic coral ecosystems—a lifeboat for coral reefs? The United Nations Environment Programme and GRID-Arendal, Nairobi, pp 21–22

Bridge T, Done T, Beaman R, Friedman A, Williams S, Pizarro O, Webster J (2011a) Topography, substratum and benthic macrofaunal relationships on a tropical mesophotic shelf margin, central Great Barrier Reef, Australia. Coral Reefs 30(1):143–153

Bridge TCL, Done TJ, Friedman A, Beaman RJ, Williams SB, Pizarro O, Webster JM (2011b) Variability in mesophotic coral reef com-munities along the Great Barrier Reef, Australia. Mar Ecol Prog Ser 428:63–75

Bridge T, Beaman R, Done T, Webster J (2012a) Predicting the location and spatial extent of submerged coral reef habitat in the Great Barrier Reef World Heritage Area, Australia. PLoS ONE 7(10):e48203


874

Bridge T, Fabricius K, Bongaerts P, Wallace C, Muir P, Done T, Webster J (2012b) Diversity of Scleractinia and Octocorallia in the mesophotic zone of the Great Barrier Reef, Australia. Coral Reefs 31(1):179–189

Bridge TCL, Beaman RJ, Bongaerts P, Muir PR, Ekins M, Sih T (2019) The Great Barrier Reef and Coral Sea. In: Loya Y, Puglise KA, Bridge TCL (eds) Mesophotic coral ecosystems. Springer, New York, pp 351–367

Browne NK (2012) Spatial and temporal variations in coral growth on an inshore turbid reef subjected to multiple disturbances. Mar Environ Res 77:71–83

Cabioch G, Camoin G, Webb GE, Le Cornec F, Garcia Molina M, Pierre C, Joachimski MM (2006) Contribution of microbialites to the development of coral reefs during the last deglacial period: case study from Vanuatu (South-west Pacific). Sediment Geol 185(3–4):297–318

Camoin G, Webster J (2014) Coral reefs and sea-level change. In: Stein R, Blackman DK, Inagaki F, Larsen H-C (eds) Developments in marine geology, vol 7. Elsevier, Amsterdam, pp 395–441

Camoin G, Cabioch G, Eisenhauer A, Braga JC, Hamelin B, Lericolais G (2006) Environmental significance of microbialites in reef environments during the last deglaciation. Sediment Geol 185(3–4):277–295

Camoin GF, Iryu Y, McInroy DB, IODP-Expedition 310 Scientists (2007) IODP expedition 310 reconstructs sea level, climatic, and environmental changes in the South Pacific during the last deglacia-tion. Sci Drill 5:4–12

Carter RM, Johnson DP (1986) Sea-level controls on the post-glacial development of the Great Barrier Reef, Queensland. Mar Geol 71(1):137–164

Chappell J (1974) Geology of coral terraces, Huon Peninsula, New Guinea: a study of quaternary tectonic movements and sea-level changes. GSA Bull 85(4):553–570

Coleman F, Dennis G, Jaap W, Schmahl GP, Koenig C, Reed S, Beaver C (2004) Part 1: status and trends in habitat character-ization of the Florida Middle Grounds. Final Report to the National Oceanic and Atmospheric Administration Coral Reef Conservation Program

Colin PL (2016) Mesophotic coral ecosystems examined—spotlight on the Palau Island group. In: Baker EK, Puglise KA, Harris PT (eds) Mesophotic coral ecosystems—a lifeboat for coral reefs? The United Nations Environment Programme and GRID-Arendal, Nairobi, pp 31–36

Colin PL, Devaney DM, Hillis-Colinvaux L, Suchanek TH, Harrison JT (1986) Geology and biological zonation of the reef slope, 50–360 m depth at Enewetak Atoll, Marshall Islands. Bull Mar Sci 38(1):111–128

Cortés JN, Risk MJ (1985) A reef under siltation stress: Cahuita, Costa Rica. Bull Mar Sci 36(2):339–356

Deschamps P, Durand N, Bard E, Hamelin B, Camoin G, Thomas AL, Henderson GM, Okuno J, Yokoyama Y (2012) Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago. Nature 483:559–564

Dill MA, Seyrafian A, Vaziri-Moghaddam H (2012) Palaeoecology of the Oligocene-Miocene Asmari formation in the Dill Anticline (Zagros Basin, Iran). Neues Jahrb Geol Paläont–Abh 263(2):167–184

Dullo W-C (2005) Coral growth and reef growth: a brief review. Facies 51(1):33–48

Dutton A, Lambeck K (2012) Ice volume and sea level during the last interglacial. Science 337(6091):216–219

Engels MS, Fletcher CH, Field ME, Storlazzi CD, Grossman EE, Rooney JJB, Conger CL, Glenn C (2004) Holocene reef accre-tion: Southwest Molokai, Hawaii, U.S.A. J Sediment Res 74(2):255–269

Fairbanks RG (1989) A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation. Nature 342:637–642

Fletcher CH, Sherman CE (1995) Submerged shorelines on Oʻahu, Hawaiʻi: archive of episodic transgression during the last deglacia-tion? J Coast Res Spec Issue 17:141–152

Fletcher CH, Bochicchio C, Conger CL, Engels MS, Feirstein EJ, Frazer N, Glenn CR, Grigg RW, Grossman EE, Harney JN, Isoun E, Murray-Wallace CV, Rooney JJ, Rubin KH, Sherman CE, Vitousek S (2008) Geology of Hawaii reefs. In: Riegl B, Dodge RE (eds) Coral reefs of the USA. Springer, New York, pp 435–488

García-Sais J (2010) Reef habitats and associated sessile-benthic and fish assemblages across a euphotic–mesophotic depth gradient in Isla Desecheo, Puerto Rico. Coral Reefs 29(2):277–288

Ginsburg RN, Harris PM, Eberli GP, Swart PK (1991) The growth potential of a bypass margin, Great Bahama Bank. J Sediment Res 61(6):976–987

Goreau TF, Goreau NI (1973) The ecology of Jamaican coral reefs II: geomorphology, zonation and sedimentary phases. Bull Mar Sci 23:399–464

Goreau TF, Land LS (1974) Fore-reef morphology and depositional processes, North Jamaica. In: Laporte LF (ed) Reefs in time and space, vol 18. Special Publication of the Society of Economic Paleontologists and Mineralogists, Tulsa, pp 77–89

Grammer GM, Ginsburg RN, Swart PK, McNeill DF, Jull AJT, Prezbindowski DR (1993) Rapid growth rates of syndepositional marine aragonite cements in steep marginal slope deposits, Bahamas and Belize. J Sediment Res 63(5):983–989

Grammer GM, Crescini CM, McNeill DF, Taylor LH (1999) Quantifying rates of syndepositional marine cementation in deeper platform environments-new insight into a fundamental process. J Sediment Res 69(1):202–207

Grigg R (2006) Depth limit for reef building corals in the Auʻau Channel, S.E. Hawaii. Coral Reefs 25(1):77–84

Grigg R, Grossman E, Earle S, Gittings S, Lott D, McDonough J (2002) Drowned reefs and antecedent karst topography, Auʻau Channel, S.E. Hawaiian Islands. Coral Reefs 21(1):73–82

Hallock P, Schlager W (1986) Nutrient excess and the demise of coral reefs and carbonate platforms. Palaios 1(4):389–398

Hanebuth TJJ, Stattegger K, Bojanowski A (2009) Termination of the last glacial maximum sea-level lowstand: the Sunda-Shelf data revisited. Glob Planet Chang 66(1):76–84

Harris PT (1994) Comparison of tropical, carbonate and temperate, siliciclastic tidally dominated sedimentary deposits: examples from the Australian continental shelf. Aust J Earth Sci 41(3):241–254

Harris PT (2016) Mesophotic coral ecosystems examined—Gulf of Carpentaria, Australia. In: Baker EK, Puglise KA, Harris PT (eds) Mesophotic coral ecosystems—a lifeboat for coral reefs? The United Nations Environment Programme and GRID-Arendal, Nairobi, pp 37–38

Harris PT, Davies PJ (1989) Submerged reefs and terraces on the shelf edge of the Great Barrier Reef, Australia. Coral Reefs 8(2):87–98

Harris PT, Heap AD (2009) Cyclone-induced net sediment transport pathway on the continental shelf of tropical Australia inferred from reef talus deposits. Cont Shelf Res 29(16):2011–2019

Harris PT, Heap AD, Marshall JF, McCulloch M (2008) A new coral reef province in the Gulf of Carpentaria, Australia: colonisation, growth and submergence during the early holocene. Mar Geol 251(1–2):85–97

Harris PT, Bridge TCL, Beaman RJ, Webster JM, Nichol SL, Brooke BP (2013) Submerged banks in the Great Barrier Reef, Australia, greatly increase available coral reef habitat. ICES J Mar Sci 70(2):284–293

Hernandez R, Sherman C, Weil E, Yoshioka P (2009) Spatial and temporal patterns in reef sediment accumulation and composi-tion, southwestern insular shelf of Puerto Rico. Caribb J Sci 45(2–3):138–150

Heyward A, Radford B (2019) Northwest Australia. In: Loya Y, Puglise KA, Bridge TCL (eds) Mesophotic coral ecosystems. Springer, New York, pp 337–349


875

Hinderstein L, Marr J, Martinez F, Dowgiallo M, Puglise K, Pyle R, Zawada D, Appeldoorn R (2010) Theme section on “Mesophotic coral ecosystems: characterization, ecology, and management.” Coral Reefs 29(2):247–251

Hine AC, Mullins HT (1983) Modern carbonate shelf-slope breaks. SEPM Spec Publ 33:169–188

Hine AC, Halley RB, Locker SD, Jarrett BD, Jaap WC, Mallinson DJ, Ciembronowicz KT, Ogden NB, Donahue BT, Naar DF (2008) Coral reefs, present and past, on the West Florida Shelf and plat-form margin. In: Riegl BM, Dodge RE (eds) Coral reefs of the USA. Springer, Dordrecht, pp 127–173

Hinestrosa G, Webster JM, Beaman RJ (2016) Postglacial sedi-ment deposition along a mixed carbonate-siliciclastic margin: new constraints from the drowned shelf-edge reefs of the Great Barrier Reef, Australia. Palaeogeogr Palaeoclimatol Palaeoecol 446:168–185

Hopkins TS, Blizzard DR, Brawley SA, Earle SA, Grimm DE, Gilbert DK, Johnson PG, Livingston EH, Lutz CH, Shaw JK, Shaw BB (1977) A preliminary characterization of the biotic components of composite strip transects on the Florida Middle Grounds, northeast-ern Gulf of Mexico. In: Taylor DL (ed) Proceedings of the Third International Coral Reef Symposium, Miami, pp 31–37

Hopley D (2006) Coral reef growth on the shelf margin of the Great Barrier Reef with special reference to the Pompey complex. J Coast Res 22:150–158

Hopley D, Smithers SG, Parnell K (2007) The geomorphology of the Great Barrier Reef: development, diversity and change. Cambridge University Press, Cambridge

Hoskin CM, Reed JK, Mook DH (1986) Production and off- bank trans-port of carbonate sediment, Black Rock, southwest Little Bahama Bank. Mar Geol 73(1):125–144

Hubbard DK (1986) Sedimentation as a control of reef development: St. Croix, U.S.V.I. Coral Reefs 5(3):117–125

Hubbard DK (1992) Hurricane-induced sediment transport in open- shelf tropical systems: an example from St. Croix, U.S. Virgin Islands. J Sediment Res 62(6):946–960

Hubbard DK, Scaturo D (1985) Growth rates of seven species of scler-actinian corals from Cane Bay and Salt River, St. Croix, USVI. Bull Mar Sci 36(2):325–338

Hubbard DK, Sadd JL, Roberts HH (1981) The role of physical pro-cesses in controlling sediment transport patterns on the insular shelf of St. Croix, U.S. Virgin Islands. In: Proceedings of the Fourth International Coral Reef Symposium, Manila, pp 399–404

Hubbard DK, Miller AI, Scaturo D (1990) Production and cycling of calcium carbonate in a shelf-edge reef system (St. Croix, U.S. Virgin Islands); applications to the nature of reef systems in the fossil record. J Sediment Res 60(3):335–360

Hubbard DK, Gill IP, Burke RB, Morelock J (1997) Holocene reef backstepping–southwestern Puerto Rico shelf. In: Lessios HA, Macintyre IG, McGee M (eds) Proceedings of the Eighth International Coral Reef Symposium, vol 2, pp 1779–1784

Hubbard DK, Zankl H, van Heerden I, Gill IP (2005) Holocene reef development along the northeastern St. Croix shelf, Buck Island, U.S. Virgin Islands. J Sediment Res 75(1):97–113

Hubbard DK, Burke RB, Gill IP, Ramirez WR, Sherman CE (2008) Coral-reef geology: Puerto Rico and the US Virgin Islands. In: Riegl BM, Dodge RE (eds) Coral reefs of the USA. Springer, Dordrecht, pp 263–302

Hubbard DK, Gill IP, Burke RB (2013) Holocene reef building on east-ern St. Croix, US Virgin Islands: Lang Bank revisited. Coral Reefs 32(3):653–669

Hughes TP (1999) Off-reef transport of coral fragments at Lizard Island, Australia. Mar Geol 157(1–2):1–6

Hutchinson Y, Sherman C (2013) Composition of lithic substrates from mesophotic habitats in Puerto Rico and US Virgin Islands. Geol Soc Am Abstr Programs 45(2):9

International Hydrographic Organization [IHO] (2013) Standardization of undersea feature names: guidelines, proposal form, terminology, Edition 4.1.0. International Hydrographic Bureau/Intergovernmental Oceanographic Commission, Monaco

Insalaco E (1996) Upper Jurassic microsolenid biostromes of north-ern and central Europe: facies and depositional environment. Palaeogeogr Palaeoclimatol Palaeoecol 121(3):169–194

James NP, Bourque P-A (1992) Reefs and mounds. In: Walker RG, James NP (eds) Facies models: response to sea level change. Geological Association of Canada, St Johns, pp 323–348

James NP, Ginsburg RN (1979) The seaward margin of the Belize bar-rier and atoll reefs, Special Publication No. 3 of the International Association of Sedimentologists. Blackwell Scientific Publications, Boston

Jarrett BD, Hine AC, Halley RB, Naar DF, Locker SD, Neumann AC, Twichell D, Hu C, Donahue BT, Jaap WC, Palandro D, Ciembronowicz K (2005) Strange bedfellows—a deep-water her-matypic coral reef superimposed on a drowned barrier island; southern Pulley Ridge, SW Florida platform margin. Mar Geol 214(4):295–307

Johnston MA, Nuttall MF, Eckert RJ, Embesi JA, Slowey NC, Hickerson EL, Schmahl GP (2013) Long-term monitoring at the east and west Flower Garden Banks National Marine Sanctuary, 2009–2010, vol-ume 1: technical report. U.S. Dept. of Interior, Bureau of Ocean Energy Management, Gulf of Mexico OCS Region, New Orleans

Kahng S, García-Sais J, Spalding H, Brokovich E, Wagner D, Weil E, Hinderstein L, Toonen R (2010) Community ecology of mesophotic coral reef ecosystems. Coral Reefs 29(2):255–275

Kennett JP (1982) Marine geology. Prentice Hall, Englewood CiffsKleypas JA (1996) Coral reef development under naturally turbid con-

ditions: fringing reefs near Broad Sound, Australia. Coral Reefs 15(3):153–167

Kopp RE, Simons FJ, Mitrovica JX, Maloof AC, Oppenheimer M (2009) Probabilistic assessment of sea level during the last intergla-cial stage. Nature 462(7275):863–867

Kühlmann DHH (1983) Composition and ecology of deep-water coral associations. Helgoländer Meeresunters 36(2):183–204

Lambeck K, Chappell J (2001) Sea level change through the last glacial cycle. Science 292(5517):679–686

Lambeck K, Rouby H, Purcell A, Sun Y, Sambridge M (2014) Sea level and global ice volumes from the last glacial maximum to the Holocene. Proc Natl Acad Sci 111(43):15296–15303

Land LS, Goreau TF (1970) Submarine lithification of Jamaican reefs. J Sediment Res 40(1):457–462

Larcombe P, Carter RM (2004) Cyclone pumping, sediment partition-ing and the development of the Great Barrier Reef shelf system: a review. Quat Sci Rev 23(1–2):107–135

Lesser MP, Slattery M, Leichter JJ (2009) Ecology of mesophotic coral reefs. J Exp Mar Biol Ecol 375(1–2):1–8

Lesser MP, Slattery M, Stat M, Ojimi M, Gates RD, Grottoli A (2010) Photoacclimatization by the coral Montastraea cavernosa in the mesophotic zone: light, food, and genetics. Ecology 91(4):990–1003

Liddell WD, Ohlhorst SL (1988) Hard substrata community patterns, 1–120 m, North Jamaica. Palaios 3(4):413–423

Liddell WD, Avery WE, Ohlhorst SL (1997) Patterns of benthic community structure, 10–250 m, the Bahamas. In: Lessios HA, Macintyre IG (eds) Proceedings of the 8th International Coral Reef Symposium. Smithsonian Tropical Research Institute, Panama, pp 437–442

Linklater M, Carroll AG, Hamylton SM, Jordan AR, Brooke BP, Nichol SL, Woodroffe CD (2016) High coral cover on a mesophotic, sub-tropical island platform at the limits of coral reef growth. Cont Shelf Res 130:34–46

Locker SD, Hine AC, Tedesco LP, Shinn EA (1996) Magnitude and tim-ing of episodic sea-level rise during the last deglaciation. Geology 24(9):827–830


876

Locker S, Armstrong R, Battista T, Rooney J, Sherman C, Zawada D (2010) Geomorphology of mesophotic coral ecosystems: current perspectives on morphology, distribution, and mapping strategies. Coral Reefs 29(2):329–345

Locker SD, Reed JK, Farrington S, Harter S, Hine AC, Dunn S (2016) Geology and biology of the “Sticky Grounds,” shelf-margin car-bonate mounds, and mesophotic ecosystem in the eastern Gulf of Mexico. Cont Shelf Res 125:71–87

Macintyre IG (1977) Distribution of submarine cements in a modern Caribbean fringing reef, Galeta Point, Panama. J Sediment Res 47(2):503–516

Macintyre IG (1988) Modern coral reefs of Western Atlantic: new geo-logical perspective. Am Assoc Pet Geol Bull 72:1360–1369

Macintyre IG (2007) Demise, regeneration, and survival of some Western Atlantic reefs during the Holocene transgression. In: Aronson RB (ed) Geological approaches to coral reef ecology. Springer, New York, pp 181–200

Macintyre IG, Marshall JF (1988) Submarine lithification in coral reefs: some facts and misconceptions. In: Choat JH, Barnes D, Borowitzka MA et al (eds) Proceedings of the 6th International Coral Reef Symposium, Vol. 1, pp 263–272

Macintyre IG, Rutzler K, Norris JN, Smith KP, Cairns SD, Bucher KE, Steneck RS (1991) An early Holocene reef in the Western Atlantic: submersible investigations of a deep relict reef off the west coast of Barbados, W.I. Coral Reefs 10:167–174

Mallinson D, Hine A, Naar D, Locker S, Donahue B (2014) New per-spectives on the geology and origin of the Florida Middle Ground carbonate banks, West Florida Shelf, USA. Mar Geol 355:54–70

Mateu-Vicens G, Pomar L, Ferràndez-Cañadell C (2012) Nummulitic banks in the upper Lutetian ‘Buil level,’ Ainsa Basin, South Central Pyrenean Zone: the impact of internal waves. Sedimentology 59(2):527–552

Mesolella KJ (1967) Zonation of uplifted Pleistocene coral reefs on Barbados, West Indies. Science 156(3775):638–640

Mesolella KJ, Sealy HA, Matthews RK (1970) Facies geometries within Pleistocene reefs of Barbados, West Indies. Am Assoc Pet Geol Bull 54:1899–1917

Montaggioni LF (2005) History of Indo-Pacific coral reef systems since the last glaciation: development patterns and controlling factors. Earth-Sci Rev 71(1–2):1–75

Montaggioni LF, Braithwaite CJR (2009) Quaternary coral reef sys-tems: history, development processes and controlling factors, Developments in Marine Geology, vol 5. Elsevier, Amsterdam

Moore CH Jr, Graham EA, Land LS (1976) Sediment transport and dispersal across the deep fore-reef and island slope (−55 m to −305 m), Discovery Bay, Jamaica. J Sediment Petrol 46:174–187

Morgan KM, Kench PS (2014) A detrital sediment budget of a Maldivian reef platform. Geomorphology 222:122–131

Morsilli M, Bosellini FR, Pomar L, Hallock P, Aurell M, Papazzoni CA (2012) Mesophotic coral buildups in a prodelta setting (late Eocene, southern Pyrenees, Spain): a mixed carbonate–siliciclastic system. Sedimentology 59(3):766–794

Muir PR, Pichon M (2019) Biodiversity of reef-building, scerlactinian corals. In: Loya Y, Pu-glise KA, Bridge TCL (eds) Mesophotic coral ecosystems. Springer, New York, pp 589–620

Mulder T, Joumes M, Hanquiez V, Gillet H, Reijmer JJG, Tournadour E, Chabaud L, Principaud M, Schnyder JSD, Borgomano J, Fauquembergue K, Ducassou E, Busson J (2017) Carbonate slope morphology revealing sediment transfer from bank-to-slope (Little Bahama Bank, Bahamas). Mar Pet Geol 83:26–34

Nacorda HME, Dizon RM, Meñez LAB, Nañola J, Cleto L, Roa-Chio PBL, De Jesus DO, Hernandez HB, Quimpo F-ATR, Licuanan WRY, Aliño PM, Villanoy CL (2017) Beneath 50 m of NW Pacific water: coral reefs on the Benham Bank Seamount off the Philippine sea. J Environ Sci Manag 20:110–121

Novak V, Santodomingo N, Rösler A, Di Martino E, Braga JC, Taylor PD, Johnson KG, Renema W (2013) Environmental reconstruction

of a late Burdigalian (Miocene) patch reef in deltaic deposits (East Kalimantan, Indonesia). Palaeogeogr Palaeoclimatol Palaeoecol 374:110–122

Ogston AS, Storlazzi CD, Field ME, Presto MK (2004) Sediment resuspension and transport patterns on a fringing reef flat, Molokai, Hawaii. Coral Reefs 23:559–569

Ohlhorst SL, Liddell WD (1988) The effect of substrata microtopogra-phy on reef community structure, 60–120 m. In: Choat JH, Barnes D, Borowitzka MA et al (eds) Proceedings of the Sixth International Coral Reef Symposium. Townsville, pp 355–360

Pandolfi JM, Llewellyn G, Jackson JBC (1999) Pleistocene reef envi-ronments, constituent grains, and coral community structure: Curaçao, Netherlands Antilles. Coral Reefs 18(2):107–122

Perry CT (2007) Tropical coastal environments: coral reefs and man-groves. In: Perry CT, Taylor K (eds) Environmental sedimentology. Blackwell Publishing, Oxford, pp 302–350

Pomar L, Baceta JI, Hallock P, Mateu-Vicens G, Basso D (2017) Reef building and carbonate production modes in the west-central Tethys during the Cenozoic. Mar Pet Geol 83:261–304

Poty E, Chevalier E (2007) Late Frasnian phillipsastreid biostromes in Belgium. Geol Soc Lond, Spec Publ 275(1):143–161

Prager EJ, Ginsburg RN (1989) Carbonate nodule growth on Florida’s outer shelf and its implications for fossil interpretations. Palaios 4(4):310–312

Pyle RL (1996) A learner’s guide to closed-circuit rebreather opera-tions. In: Proceedings of the rebreather forum 2.0. Redondo Beach, pp P45–P67

Rankey EC, Doolittle DF (2012) Geomorphology of carbonate platform- marginal uppermost slopes: insights from a Holocene analogue, Little Bahama Bank, Bahamas. Sedimentology 59:2146–2171

Reed JK, Farrington S, Harter S, David A, Moe H, Hanisak D (2017) Characterization of the mesophotic benthic habitat, benthic macro-biota, and fish assemblages from ROV dives on Pulley Ridge during the 2015 R/V Walton Smith cruise. Harbor Branch Oceanographic Institute Technical Report, vol 177, 221 p http://data.nodc.noaa.gov/coris/library/NOAA/CRCP/other/non_crcp_publications/NCCOS_Pulley_Ridge_Report.pdf

Reed JK, Farrington S, David A, Harter S, Pomponi S, Diaz MC, Voss JD, Spring KD, Hine AC, Kourafalou V, Smith RH, Vaz AC, Paris CB, Hanisak MD (2019) Pulley Ridge, Gulf of Mexico, USA. In: Loya Y, Puglise KA, Bridge TCL (eds) Mesophotic coral ecosys-tems. Springer, New York, pp 57–69

Reich CD, Poore RZ, Hickey TD (2013) The role of vermetid gastro-pods in the development of the Florida Middle Ground, northeast Gulf of Mexico. J Coast Res Spec Issue 63:46–57

Reid RP, Macintyre IG (1988) Foraminiferal-algal nodules from the eastern Caribbean; growth history and implications on the value of nodules as paleoenvironmental indicators. Palaios 3(4):424–435

Rezak R, Bright TJ, McGrail DW (1985) Reefs and banks of the north-western Gulf of Mexico: their geological, biological, and physical dynamics. Wiley, New York

Rivera J, Prada M, Arsenault JL, Moody G, Benoit N (2006) Detecting fish aggregations from reef habitats mapped with high resolu-tion side scan sonar imagery. NOAA Professional Paper NMFS 5:88–104

Roberts HH, Murray SP, Suhayda JN (1977) Physical processes in a fore-reef shelf environment. In: Proceedings Third International Coral Reef Symposium. Miami, pp 507–515

Rogers CS (1990) Responses of coral reefs and reef organisms to sedi-mentation. Mar Ecol Prog Ser 62:185–202

Rohling EJ, Grant K, Bolshaw M, Roberts AP, Siddall M, Hemleben C, Kucera M (2009) Antarctic temperature and global sea level closely coupled over the past five glacial cycles. Nat Geosci 2(7):500–504

Rohling EJ, Foster GL, Grant KM, Marino G, Roberts AP, Tamisiea ME, Williams F (2014) Sea-level and deep-sea-temperature vari-ability over the past 5.3 million years. Nature 508(7497):477–482


http://data.nodc.noaa.gov/coris/library/NOAA/CRCP/other/non_crcp_publications/NCCOS_Pulley_Ridge_Report.pdf



877

Rooney JJ, Wessel P, Hoeke R, Weiss J, Baker J, Parrish F, Fletcher CH, Chojnacki J, Garcia M, Brainard R, Vroom P (2008) Geology and geomorphology of coral reefs in the northwestern Hawaiian Islands. In: Riegl B, Dodge RE (eds) Coral reefs of the USA. Springer, Dordrecht, pp 519–572

Rooney J, Donham E, Montgomery A, Spalding H, Parrish F, Boland R, Fenner D, Gove J, Vetter O (2010) Mesophotic coral ecosystems in the Hawaiian Archipelago. Coral Reefs 29(2):361–367

Rosen BR, Aillud GS, Bosellini FR, Clarke NJ, Insalaco E, Valldeperas FX, Mej W (2000) Platy coral assemblages: 200 million years of functional stability in response to the limiting effects of light and turbidity. In: Moosa MK, Soemodihardjo S, Soegiarto A et al (eds) Proceedings of the Ninth International Coral Reef Symposium. International Society for Reef Studies, Bali, pp 255–264

Sanborn KL, Webster JM, Yokoyama Y, Dutton A, Braga JC, Clague DA, Paduan JB, Wagner D, Rooney JJ, Hansen JR (2017) New evi-dence of Hawaiian coral reef drowning in response to meltwater pulse-1A. Quat Sci Rev 175(Supplement C):60–72

Schmahl GP, Hickerson EL, Precht WF (2008) Biology and ecology of coral reefs and coral communities in the Flower Garden Banks region, northwestern Gulf of Mexico. In: Riegl BM, Dodge RE (eds) Coral reefs of the USA. Springer, Dordrecht, pp 221–261

Scoffin TP (1987) An introduction to carbonate sediments and rocks. Chapman and Hall, New York

Scoffin TP, Tudhope AW (1985) Sedimentary environments of the Central Region of the Great Barrier Reef of Australia. Coral Reefs 4(2):81–93

Seard C, Camoin G, Yokoyama Y, Matsuzaki H, Durand N, Bard E, Sepulcre S, Deschamps P (2011) Microbialite development pat-terns in the last deglacial reefs from Tahiti (French Polynesia; IODP Expedition #310): implications on reef framework architecture. Mar Geol 279(1–4):63–86

Shackleton NJ (1987) Oxygen isotopes, ice volume and sea level. Quat Sci Rev 6:183–190

Shao L, Li Q, Zhu W, Zhang D, Qiao P, Liu X, You L, Cui Y, Dong X (2017) Neogene carbonate platform development in the NW South China Sea: Litho-, bio- and chemo-stratigraphic evidence. Mar Geol 385:233–243

Sherman C, Appeldoorn R (2015) Geomorphology of mesophotic coral ecosystems in Puerto Rico and US Virgin Islands [Abstract]. 37th Scientific Meeting of the Association of Marine Laboratories of the Caribbean, Curaçao

Sherman CE, Fletcher CH III, Rubin KH (1999) Marine and meteoric diagenesis of Pleistocene carbonates from a nearshore submarine terrace, Oahu, Hawaii. J Sediment Res 69(5):1083–1097

Sherman C, Appeldoorn R, Carlo M, Nemeth M, Ruiz H, Bejarano I (2009) Use of technical diving to study deep reef environments in Puerto Rico. In: Pollock NW (ed) Proceedings of the American Academy of Underwater Sciences 28th Scientific Symposium. American Academy of Underwater Sciences, Dauphin Island, pp 58–65

Sherman C, Nemeth M, Ruíz H, Bejarano I, Appeldoorn R, Pagán F, Schärer M, Weil E (2010) Geomorphology and benthic cover of mesophotic coral ecosystems of the upper insular slope of Southwest Puerto Rico. Coral Reefs 29(2):347–360

Sherman C, Appeldoorn R, Ballantine D, Bejarano I, Carlo M, Kesling D, Nemeth M, Pagan F, Ruiz H, Schizas N, Weil E (2013a) Exploring the mesophotic zone: diving operations and scientific highlights of three research cruises across Puerto Rico and US Virgin Islands. In: Lang MA, Sayer MDJ (eds) Proceedings of the 2013 AAUS/ESDP Curaçao Joint International Scientific Diving Symposium. American Academy of Underwater Sciences, Dauphin Island, pp 297–312

Sherman C, Hernandez R, Hutchinson Y, Whitall D (2013b) Terrigenous sedimentation patterns at reefs adjacent to the Guánica Bay Watershed. In: Whitall D, Bauer LJ, Sherman C et al (eds) Baseline

assessment of Guánica Bay, Puerto Rico in support of water-shed restoration. NOAA Technical Memorandum NOS NCCOS 176. NCCOS Center for Coastal Monitoring and Assessment Biogeography Branch, Silver Spring, pp 103–112

Sherman CE, Fletcher CH, Rubin KH, Simmons KR, Adey WH (2014) Sea-level and reef accretion history of marine oxygen isotope stage 7 and late stage 5 based on age and facies of submerged late Pleistocene reefs, Oahu, Hawaii. Quat Res 81(1):138–150

Sherman C, Schmidt W, Appeldoorn R, Hutchinson Y, Ruiz H, Nemeth M, Bejarano I, Cruz Motta JJ, Xu H (2016) Sediment dynamics and their potential influence on insular-slope mesophotic coral ecosys-tems. Cont Shelf Res 129:1–9

Siddall M, Rohling EJ, Almogi-Labin A, Hemleben C, Meischner D, Schmelzer I, Smeed DA (2003) Sea-level fluctuations during the last glacial cycle. Nature 423:853–858

Smith TB, Holstein D (2016) Mesophotic coral ecosystems exam-ined—the United States Virgin Islands, USA. In: Baker EK, Puglise KA, Harris PT (eds) Mesophotic coral ecosystems—a lifeboat for coral reefs? The United Nations Environment Programme and GRID- Arendal, Nairobi, pp 26–27

Smith T, Blondeau J, Nemeth R, Pittman S, Calnan J, Kadison E, Gass J (2010) Benthic structure and cryptic mortality in a Caribbean meso-photic coral reef bank system, the Hind Bank Marine Conservation District, U.S. Virgin Islands. Coral Reefs 29(2):289–308

Smith TB, Brandtneris VW, Canals M, Brandt ME, Martens J, Brewer RS, Kadison E, Kammann M, Keller J, Holstein DM (2016) Potential structuring forces on a shelf edge upper mesophotic coral ecosystem in the US Virgin Islands. Front Mar Sci 3:115

Smith TB, Brandt ME, Brandtneris VW, Ennis RS, Groves SH, Habtes S, Holstein DM, Kadison E, Nemeth RS (2019) The United States Virgin Islands. In: Loya Y, Puglise KA, Bridge TCL (eds) Mesophotic coral ecosystems. Springer, New York, pp 131–147

Stanley GD (1988) The history of early Mesozoic reef communities; a three-step process. Palaios 3(2):170–183

Stolarski J, Kitahara MV, Miller DJ, Cairns SD, Mazur M, Meibom A (2011) The ancient evolutionary origins of Scleractinia revealed by azooxanthellate corals. BMC Evol Biol 11(1):316

Storlazzi CD, Ogston AS, Bothner MH, Field ME, Presto MK (2004) Wave- and tidally-driven flow and sediment flux across a fringing coral reef: southern Molokai, Hawaii. Cont Shelf Res 24(12):1397–1419

Stumm EC (1964) Silurian and devonian corals of the falls of the Ohio. Geol Soc Am Mem 93:1–184

Tornqvist TE, Hijma MP (2012) Links between early Holocene ice- sheet decay, sea-level rise and abrupt climate change. Nat Geosci 5(9):601–606

Törnqvist TE, Bick SJ, González JL, van der Borg K, de Jong AFM (2004) Tracking the sea-level signature of the 8.2 ka cooling event: new constraints from the Mississippi Delta. Geophys Res Lett 31(23):L23309

Torres JL, Morelock J (2002) Effect of terrigenous sediment influx on coral cover and linear extension rates of three Caribbean massive coral species. Caribb J Sci 38(3–4):222–229

Torresan ME, Gardner JV (2000) Acoustic mapping of the regional seafloor geology in and around Hawaiian ocean dredged-material disposal sites. U.S. Geological Survey Open-File Report 00–124

Toscano MA, Macintyre IG (2003) Corrected Western Atlantic sea-level curve for the last 11,000 years based on calibrated 14C dates from Acropora palmata framework and intertidal mangrove peat. Coral Reefs 22:257–270

Tucker ME, Wright VP (1990) Carbonate sedimentology. Blackwell Publishing, Oxford

Watanabe T, Watanabe TK, Yamazaki A, Yoneta S, Sowa K, Sinniger F, Eyal G, Loya Y, Harii S (2019) Coral sclerochronology: similarities and differences in the coral isotopic signatures between mesophotic


878

and shallow-water reefs. In: Loya Y, Puglise KA, Bridge TCL (eds) Mesophotic coral ecosystems. Springer, New York, pp 667–681

Webster JM, Clague DA, Riker-Coleman K, Gallup C, Braga JC, Potts D, Moore JG, Winterer EL, Paull CK (2004) Drowning of the −150 m reef off Hawaii: a casualty of global meltwater pulse 1A? Geology 32(3):249–252

Webster JM, Yokoyama Y, Cotterill C, Scientists E (2011) Proceedings of the Integrated Ocean Drilling Program volume 325. Integrated Ocean Drilling Program Management International, Inc., Tokyo

Webster JM, Braga JC, Humblet M, Potts DC, Iryu Y, Yokoyama Y, Fujita K, Bourillot R, Esat TM, Fallon S, Thompson WG, Thomas AL, Kan H, McGregor HV, Hinestrosa G, Obrochta SP, Lougheed BC (2018) Response of the Great Barrier Reef to sea-level and environmental changes over the past 30,000 years. Nat Geosci 11(6):426–432

Weinstein DK (2014) Deep reef bioerosion and deposition: sedi-mentology of mesophotic coral reefs in the U.S. Virgin Islands. Dissertation, University of Miami

Weinstein DK, Smith TB, Klaus JS (2014) Mesophotic bioerosion: variability and structural impact on U.S. Virgin Island deep reefs. Geomorphology 222:14–24

Weinstein DK, Klaus JS, McNeill DF (2015a) Syndepositional cemen-tation in the reef ‘twilight zone.’ Reef Encount 30:53–56

Weinstein DK, Klaus JS, Smith TB (2015b) Habitat heterogeneity reflected in mesophotic reef sediments. Sediment Geol 329:177–187

Weinstein DK, Sharifi A, Klaus JS, Smith TB, Giri SJ, Helmle KP (2016) Coral growth, bioerosion, and secondary accretion of living orbicellid corals from mesophotic reefs in the US Virgin Islands. Mar Ecol Prog Ser 559:45–63

Wolanski E, Colin P, Naithani J, Deleersnijder E, Golbuu Y (2004) Large amplitude, leaky, island-generated, internal waves around Palau, Micronesia. Estuar Coast Shelf Sci 60(4):705–715

Woodroffe CD, Webster JM (2014) Coral reefs and sea-level change. Mar Geol 352:248–267

Woodroffe CD, Brooke BP, Linklater M, Kennedy DM, Jones BG, Buchanan C, Mleczko R, Hua Q, Zhao J-X (2010) Response of coral reefs to climate change: expansion and demise of the south-ernmost Pacific coral reef. Geophys Res Lett 37(15):L15602

Yokoyama Y, De Deckker P, Lambeck K, Johnston P, Fifield LK (2001) Sea-level at the last glacial maximum: evidence from northwestern Australia to constrain ice volumes for oxy-gen isotope stage 2. Palaeogeogr Palaeoclimatol Palaeoecol 165(3–4):281–297

Yokoyama Y, Webster JM, Cotterill C, Braga JC, Jovane L, Mills H, Morgan S, Suzuki A, IODP-Expedition-325-Scientists (2011) IODP expedition 325: the Great Barrier Reef reveals past sea-level, cli-mate, and environmental changes since the last Ice Age. Sci Drill 12:32–45

Yoshioka PM (2009) Sediment transport and the distribution of shallow- water gorgonians. Caribb J Sci 45:254–259

Yoshioka PM, Yoshioka BB (1989) Effects of wave energy, topographic relief and sediment transport on the distribution of shallow-water gorgonians of Puerto Rico. Coral Reefs 8(3):145–152

Zapalski MK, Wrzołek T, Skompski S, Berkowski B (2017) Deep in shadows, deep in time: the oldest mesophotic coral ecosystems from the Devonian of the Holy Cross Mountains (Poland). Coral Reefs 36(3):847–860


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