Ecological design for urban waterfronts

Karen Dyson & Ken Yocom

Published online: 10 July 2014# Springer Science+Business Media New York 2014

Abstract Urban waterfronts are rarely designed to support biodiversity and other ecosystemservices, yet have the potential to provide these services. New approaches that integrateecological research into the design of docks and seawalls provide opportunities to mitigatethe environmental impacts of urbanization and recover ecosystem function in urban water-fronts. A review of current examples of ecological design in temperate cities informs sugges-tions for future action. Conventional infrastructures have significant and diverse impacts onaquatic ecosystems. The impacts of conventional infrastructure are reduced where ecologicaldesigns have been implemented, particularly by projects adding microhabitat, creating moreshallow water habitat, and reconstructing missing or altered rocky benthic habitats.Opportunities for future research include expanding current research into additional ecosys-tems, examining ecological processes and emergent properties to better address ecosystemfunction in ecological design, and addressing the impact of and best practices for continuingmaintenance. Planned ecological infrastructure to replace aging and obsolete structures willbenefit from design feedback derived from carefully executed in situ pilot studies.

Keywords Ecological design . Seawalls . Habitat .Waterfront . Urban infrastructure .

Aquatic ecology

Introduction

Marine and freshwater ecosystems provide important ecosystem services for urban areas,including protection from coastal hazards and severe storms, support for biodiversity, andopportunities for recreation (Ruckelshaus et al. 2013; Strayer and Findlay 2010). Prioritizationof certain ecosystem services (particularly transportation) have limited the waterfronts of many

Urban Ecosyst (2015) 18:189–208DOI 10.1007/s11252-014-0385-9

K. Dyson (*)University of Washington, Gould Hall 3949 15th Ave NE, Box 355740, Seattle, WA 98195-5734, USAe-mail: kld36@uw.edu

K. Dysone-mail: karenldyson@gmail.com

K. YocomUniversity of Washington, 448A Gould Hall 3949 15th Ave NE, Box 355734, Seattle,WA 98195-5734, USAe-mail: kyocom@uw.edu

urban areas to accommodate other services such as habitat provision and storm protection(Everard and Moggridge 2012; Manca et al. 2012; Martin 2010). Despite these limitations,urban waterfronts still have the capacity to provide habitat suitable for a large diversity ofaquatic organisms, making them important areas for urban conservation and ecological reha-bilitation (Clynick 2008; James et al. 2010; Kozlowski and Bondallaz 2013; Ng et al. 2012).

Over the past several decades new approaches—including ecological design—have emergedthat seek to mitigate environmental impacts and recover neglected ecosystem services byintegrating knowledge of ecosystem process and function into urban design practices (Beatley2011; De Groot et al. 2002; Francis and Lorimer 2011; Riley 1998; Rosenzweig 2001, 2003;Van Der Ryn and Cowan 2007). In the context of urban waterfronts, these approaches seek toapply knowledge of natural and urban shoreline ecosystem processes and functions to the designof in- and near-water infrastructure to mitigate the impact of urbanization (Bulleri and Chapman2009). Implementing infrastructure that supports processes to sustain or improve ecologicalfunction will compliment broader planning efforts to preserve and restore remnant habitats andbuild capacity for a greater diversity of ecosystem services in urban waterfronts (Croci et al.2008; De Groot et al. 2002; Duffy-Anderson et al. 2003; Lundholm and Richardson 2010;McKinney and Raposa 2013; Moreira et al. 2006; Russell et al. 1983)

We hypothesize that designing and installing diverse ecological infrastructure in the urbanwaterfront improves the quality of urban ecosystem function and service provision. To address thishypothesis, we focus explicitly on habitat provision, biodiversity, and community composition asthe first step towards more diverse ecosystem service provision in the urban waterfront. Through areview of existing literature and current examples of ecological design, our investigation examinesrecent developments in infrastructure design for urban waterfronts where the existing infrastructurecannot or is unlikely to be removed. We frame this work through three key questions:

1) How does conventional aquatic infrastructure design impact the aquatic ecosystem?2) What ecological infrastructure designs have been proposed for docks, seawalls, and other

aquatic infrastructure, and where implemented, what has been the result?3) What are the potential directions for future research and the opportunities for

implementing ecological infrastructure strategies along urban waterfronts?

While we recognize the important social and economic challenges surrounding urbanwaterfront operations and redevelopment, they are beyond the scope of this analysis and havebeen examined elsewhere (see Beaumont et al. 2008; Dean et al. 2011; Dearborn and Kark2010; Kaplan 2007; Loukaitou-Sideris 2012; Meyer 2008; Ruiz-Frau et al. 2012).

Methods

Literature review

To address the first two questions, we researched relevant indexes and databases (includingScirus, Scopus, Google Scholar, and ISI) and searched for articles, conference papers, andgovernment and project consultant reports related to the ecological implications of conven-tional aquatic infrastructure and any proposed design recommendations. Seed terms included“seawall habitat,” “urban infrastructure habitat,” “ecological impacts of seawalls,” and “eco-logical impacts of docks.” Searches were expanded using citation records and by examiningidentified authors’ other publications. No specific keywords were required for inclusion,however all articles and reports focused on the ecology of urban aquatic infrastructure. The

190 Urban Ecosyst (2015) 18:189–208

review identified over 200 documents from across the globe, including studies conducted inAustralia, Italy, Japan, the United States, and Canada.

Aquatic infrastructure design examples

To provide more detail regarding site specific design implementation, we include sevenexample projects of recent construction (2006–2011) covering locations on both coasts ofNorth America and the Great Lakes. These design examples are based on semi-structuredinterviews with project designers and managers, site visits, and literature review (Table 1).These case studies are integrated into the discussion in order to examine design responses toecological impacts of conventional aquatic infrastructure and to frame potential directions forextending existing research and identifying further opportunities for implementing ecologicalinfrastructure strategies along urban waterfronts.

A total of 13 interviews were conducted. Initial interviews with key individuals werecompleted between 2009 and 2012, with follow-up interviews continuing through February2014. Interviewees were selected non-randomly using purposive and snowball samplingtechniques; initial purposive sampling was based on interviewees’ relationship to and famil-iarity with the ecological infrastructure projects of interest.

Interviews were conducted using Dexter’s (1970) “elite interview” technique in person andvia e-mail. Topics covered by interview questions included technical project details (dimen-sions, cost, and installation information), monitoring methods and results, and the wider designand policy implications of the project. As some of the case studies are not described in thepeer-reviewed literature, interviews and site visits were necessary to obtain informationregarding the projects and their outcomes.

Project history searches were performed in conjunction with interviews to provide back-ground data for the interviews and to provide additional information for the case studies. Seedsearch terms included the names of projects (e.g. “Cuyahoga HUBS”), names of key individ-uals, and names of state and local government agencies and private companies affiliated withthe project.

Site visits were conducted to gather more detailed information regarding the physical andfunctional aspects of the design. When possible, site visits were concurrent with interviews andserved to prompt discussion.

Literature review

Conventional designs for aquatic infrastructure alter the ecosystem function and communitycomposition of native soft substrate and rocky shoreline habitats. Altered function and

Table 1 Methods informing eachof the case studies Example project Interviews Site visits Literature review

Cuyahoga HUBS Yes No Yes

New York reef balls Yes Yes No

Seattle substrate baskets Yes Yes Yes

Seattle habitat benches Yes Yes Yes

Seattle seawall Yes Yes Yes

Vancouver habitat island Yes No Yes

Vancouver seawall stairs Yes No Yes

Urban Ecosyst (2015) 18:189–208 191

community composition are observed on the surface of urban infrastructure in the inter- andsub-tidal zones (Airoldi et al. 2005; Bulleri 2005; Bulleri and Chapman 2009; Chapman andUnderwood 2011; Gacia et al. 2007; Glasby and Connell 2001; Megina et al. 2013; Moreiraet al. 2006). Ecologists have identified several key distinctions in habitat structure betweennaturally occurring hard substrates and the habitat introduced by conventional aquatic infra-structure: lack of microhabitat, differences in surface aspect and orientation, sedimentation,shading, and non-native species abundance. These observations have led ecologists to suggestbroad changes to conventional aquatic infrastructure design to improve the quality of ecosys-tem functioning in the urban waterfront.

Microhabitat

Microhabitat is present on rocky shorelines, but is heavily modified or absent on conventionalaquatic infrastructure (Fig. 1a). Patterns of species abundance are altered on the hard structuresassociated with docks, including fiberglass and concrete pontoons and pilings, when comparedwith natural rocky shores (Connell and Glasby 1999; Perkol-Finkel et al. 2006). Key differ-ences include the presence of more filter feeders (Perkol-Finkel et al. 2008) and non-nativespecies (Glasby et al. 2007). On seawalls where microhabitat has been entirely removed,species diversity is significantly reduced (Bulleri et al. 2004; Chapman 2003; Chapman 2006;Chapman and Bulleri 2003; Firth et al. 2013; Gacia et al. 2007).

Two important types of microhabitat missing from seawalls are tidepools and crevices,which host many of the species observed only on rocky shorelines. Tidepools provide refugefor species at low tide, while crevices provide protection against predators and physical stress,increasing survival and recruitment (Chapman 2003; Moreira et al. 2006). Microhabitatavailability may influence wider ecosystem function; for example microhabitat reliant chitonsinfluence the distribution of algae and other organisms (Bulleri et al. 2004; Moreira et al.2006). Further, biodiversity may be promoted on artificial structures by the addition of rockpools and other design features (Bulleri and Chapman 2009; Firth et al. 2013).

Fig. 1 Comparison between seawalls (top) and natural rocky shorelines (bottom) highlighting differences in a.microhabitat, b. vertical and horizontal orientation of substrate, and c. nearshore habitat area using the intertidalzone to illustrate the example

192 Urban Ecosyst (2015) 18:189–208

Orientation

The vertical and horizontal orientation of the habitat also influences communitystructure (Glasby and Connell 2001; Knott et al. 2004). While seawalls and dockpilings are vertical surfaces with little to no relief, rocky shorelines are sloped and arecomprised of a complex mix of vertical and horizontal surfaces (Fig. 1b). Differentsurface orientations are exposed to different wave action and sunlight intensities, influencingthe distribution of aquatic organisms. As with microhabitat, surface orientation is important forany aquatic infrastructure design, and surface orientation may be more important than whetherreefs are natural or artificial, suggesting opportunities for ecological design in urban waterfronts(Knott et al. 2004).

Additionally, when the shoreline is vertical instead of sloped, the nearshore habitat areaavailable to aquatic organisms is drastically reduced (Fig. 1c). Reducing the area of shallowwater habitat near shore eliminates much of the suitable habitat for shoreline vegetation andinfluences community structure (Holloway and Connell 2002; Perkol-Finkel et al. 2008). Theamount of available shallow water habitat available for foraging is positively correlated withthe density and species richness of wading birds in urban areas with low levels of humandisturbance (McKinney et al. 2010). As a result, increasing available nearshore habitat area isan important concern for the design of aquatic infrastructure.

Sedimentation

Urbanization of the waterfront can also contribute to sedimentation of rocky habitats andscouring of soft substrates (e.g. silt or sand) in the inter- and sub-tidal zones. Dense pilingsreduce water velocities in rivers, resulting in the accumulation of anoxic soft substrate withgreatly reduced biodiversity (Alevras and Zappala 2008). In New York, changes in the HudsonRiver’s hydrology caused by pilings have caused soft sediment to accumulate in anoxic driftsup to 9 m (30 ft) deep that support few organisms other than polychete worms (Alevras andZappala 2008).

Shoreline armoring in the urban waterfront can create adjacent areas of scouring and loss ofsoft substrate habitat (Twu and Liao 1999). Where this occurs, fewer species associated withsoft substrate and more species associated with hard substrates (rocky shorelines) are observed(Airoldi et al. 2005; Peterson et al. 2000). Without removing conventional shoreline armoring,restoring soft shorelines is difficult, though future developments in ecological engineering andecological infrastructure design may provide alternatives. Municipalities faced with loss of softsubstrate habitat may seek to provide physical conditions similar to rocky habitat foundelsewhere in the region, and work to preserve or restore soft substrate habitat at other sitesnearby (Lundholm and Richardson 2010).

The cumulative impact of multiple structures can result in significant impacts to aquaticecosystems—including altered sediment accumulation and dispersal, creation of new barrierislands, and transformation of estuaries from tide-dominated to wave-dominated systems(Syvitski et al. 2005; Williams et al. 2013). Changes in sediment grain size can have negativeimplications for aquatic habitat quality and availability; in Namibia an increase in coarsegrained sediment led to elimination or replacement of benthic species (McLachlan 1996) whileelsewhere increases in fine grained sediment have resulted in limited light penetration andaquatic flora mortality (Wood and Armitage 1997). More research on ecological processes inthe urban benthic environment and water column is greatly needed–particularly for under-standing the complex environmental responses to multiple infrastructure installations beyondsedimentation.

Urban Ecosyst (2015) 18:189–208 193

Shading

Docks, piers, and overwater structures introduce shade to the urban waterfront. Shading resultsin reduced plant density by inhibiting photosynthesis and increasing plant mortality, damagingcommunities of aquatic vegetation valued as nursery habitat (Castellan and Kelty 2005; Sangeret al. 2004). Shading, coupled with other impacts of urbanization, often results in the elimina-tion of upland, intertidal, and nearshore vegetation (Toft and Cordell 2006). Shading alsoimpacts fish, who may avoid large docks—and the low light conditions and the stark light/dark boundary they create—based on altered predator behavior, increased predation risk, orforaging difficulty (Able et al. 1998; Cermak 2002; Duffy-Anderson et al. 2003; Onoet al. 2010; Toft et al. 2004). Artificial lights on urban infrastructure can also affect fishabundance and behavior (Becker et al. 2012). Increasing available light—includingphotosynthetically active radiation (PAR)—is the only way to address shading impacts.

Non-native species

One of the most important changes in community composition is the increased proportion ofnon-native species found on conventional aquatic infrastructure. While native populationscommonly experience depressed reproduction and recruitment in the urban waterfront (Airoldiand Bulleri 2011; Barwick and Kwak 2004; Bulleri 2005; Moreira et al. 2006), non-nativespecies exist in higher proportions and are observed in greater numbers on built aquaticstructures than natural rocky shorelines (Bulleri 2005; Megina et al. 2013; Salomidi et al.2013). Researchers suggest that conventional aquatic infrastructure provides favorable habitatfor non-native species and may negate the competitive evolutionary advantage native specieshave on natural habitat. Collectively, these impacts may help non-native species establish onand disperse along the waterfront (Bulleri and Airoldi 2005; Connell 2001; Glasby et al. 2007;Salomidi et al. 2013; Simkanin et al. 2012; Tyrell and Byers 2007).

Design response

As shown, conventional waterfront infrastructure alters ecosystem function and communitycomposition in ways we are only beginning to understand. However, where existing structurescannot or are unlikely to be removed, ecological design modifications are being explored toreduce the observed impacts. Based on the empirical research assessing existing conditionsalong urban waterfronts, these modifications rely on two broad recommendations for manip-ulating the form of the structures to instigate functional ecological processes (Chapman andUnderwood 2011; Lukens and Selberg 2004; Moreira et al. 2006). The first suggestion is to designinfrastructure that uses natural materials or mimics the physical properties of natural habitats tosupport the habitat requirements of native species and reduce the influence of non-native species(Lukens and Selberg 2004). The texture of natural materials on their own or embedded in concretemay be preferred by native species, for example kelp adhere better to rocks with complex smallscale irregularities (Deysher et al. 2002; Lukens and Selberg 2004; Ohgai et al. 1995). Importantly,specific materials under consideration need to be tested under local conditions to judge theirsuitability for locally important native species (Chapman and Underwood 2011).

Second, ecological infrastructure design should reference locally specific and ecologicallyintact shorelines, paying particular attention to microhabitat, surface orientation, and nearshorehabitat area (Chapman 2003; Deysher et al. 2002; Moreira et al. 2006; Perkol-Finkel andBenayahu 2007). Experiments where artificial substrates were developed to resemble referenceconditions by increasing the number of micro-crevices, fractures, and tidepools found that

194 Urban Ecosyst (2015) 18:189–208

these treatments increased biodiversity (Moschella et al. 2005). While future research acrossmultiple cities is needed to build on these early results, these two recommendations form thefoundation of the ecological aquatic infrastructure designs discussed in the following sections.

Aquatic infrastructure design

Design recommendations—coupled with regulatory requirements and the requests of con-cerned urban planners, designers, and citizens—have contributed to the development ofecological designs for aquatic infrastructure. Though these projects comprise a small percent-age of existing aquatic infrastructure, they demonstrate that ecological design practiced in theurban waterfront is feasible (Rosenzweig 2003). Future waterfront projects can and shouldlearn from their successes and failures.

Seawalls and bulkheads

Seawall stairs

Seawall stairs are precast concrete steps designed to increase nearshore habitat area and addboth horizontal surfaces and microhabitat to the urban waterfront by incorporating exposedaggregate (surface texture) and depressions designed to mimic tidepools (Table 2a; EBA 2011;Slogan 2011). Seawall stairs may provide habitat, enhance food production, and improvemigration corridors for juvenile salmon and other organisms (EBA 2011).

A large seawall stair was completed in 2008 at Vancouver Convention Center West building inVancouver, Canada (there called a habitat skirt; EBA, 2011) providing more than 6,782 m2

(73,000 ft2) of habitat. The benches, which measure 6.7 m long by 1.3 m wide (22 ft by 4.2 ft),are corrugated to create crevices and also include a central lengthwise depression to act as a tide pool.These features were designed to encourage the long-term colonization of local species (EBA 2011).

Monitoring results show that the seawall stair is productive habitat, with populations ofsessile invertebrates (including Pacific blue mussel Mytilus trossulus), algae (including Fucusdistichus), and mobile invertebrates (including Strongylocentrotus droebachiensis). Predators(including Cancer productus and Pisaster ochraceus) are controlling Green sea urchin popu-lations (Strongylocentrotus droebchiensis) at habitat edges, however reduced predator accessdue to the suspended nature of the habitat may reduce predator access to other areas whereGreen sea urchins are suppressing kelp abundance (including Nereocystis luetkeana; Slogan2011). The findings also suggest that tidal height may be more important than orientation atsome tidal elevations, highlighting the importance of designs which increase shallow waterhabitat area, as well as the need for further research (EBA 2011; Slogan 2011).

Seawall texturing

Seawall texturing directly incorporates habitat into the surface of seawalls to create microhab-itats, diverse surface orientations, and additional shallow water habitat area (Table 2b).Different designs include crevices, shallow pools, and ledges (Cordell 2011; Goff 2008;Tanaka et al. 2000). In addition to habitat, seawall texturing creates an opportunity foraesthetically improving the waterfront (City of Seattle 2013).

In Seattle, city planners are taking advantage of a seawall replacement project to integratehabitat into the design of the urban waterfront (Fig. 2; Cordell 2011; Goff 2008, 2010).Historically, Seattle’s shorelines were gravel and cobble beaches backed by bluffs, however

Urban Ecosyst (2015) 18:189–208 195

currently the shoreline is dominated by the 3 km long seawall with few intertidalbeaches. Researchers designed distinct panel structures to address differences in theseawalls’ slope and availability of microhabitat. As a pilot project, the 1.5 m by 2.3 mtest panels (5 ft by 7.5 ft) were bolted to the old seawall in 2008 and monitored for4 years. (Goff 2010).

The two textures (cobbled and smooth) used in the seawall panel designs tested for theimportance of microhabitat, while three different shapes (finned, stepped, and a flat control)increased habitat area and introduced different surface orientations. Both texture and finned/stepped shapes benefited ecologically important species. A canopy forming algae (Fucusdistichus)—linked to crustacean and herbivorous gastropod diversity—was found in greaterabundance on sloped test panels with reduced wave energy. Mussels (Mytilus spp.)—importantecosystem engineers that provide food for birds and fish and also support species that live onlyin mussel beds—were more abundant on panels with cobble surfaces and associated with thecrevices (Cordell 2011; Goff 2010). These results are being used to inform the design of thenew seawall, and current designs include seawall texturing, cobble reefs, and a cantilevereddeck that light can penetrate (City of Seattle 2013).

Table 2 Ecological designs to replace traditional seawalls and other shoreline armoring

Illustra�on Design Focus Design successful?

Key Resources

a.Se

awal

l St

airs

-Reintroduce microhabitats including �depools- Increase inter�dal habitat area; - Reintroduce shallow water habitat to benefit fish, vegeta�on, etc.

Yes; Vancouver Conven�on Center

Slogan, 2011

EBA, 2011

b.Se

awal

l Te

xtur

ing

- Reintroduce microhabitats including �depools- Create diverse surface orienta�ons (horizontal, ver�cal, etc.)

Yes; Sea�le Seawall

Goff, 2008

Goff, 2010

c. H

abita

t Be

nche

s

- Increase inter�dal habitat area; - Reintroduce shallow water habitat to benefit fish, vegeta�on, etc.- Protect seawall structural integrity

Yes; Olympic Sculpture Park in Sea�le, WA

To� et al., 2012

To� et al., 2013

d. V

eget

a�on

Bas

ket

- Create refuges for migra�ng fish, including juvenile fish- Reintroduce shoreline vegeta�on

No; plants diedin trials in Cuyahoga River, OH

None in published literature.

e. H

abita

t Ba

sket

- Reintroduce microhabitats including �depools- Reintroduce so� substrates, gravel, and cobble substrates

No; waves washed sediment out of Sea�le trial

Yes, Australia

Browne and Chapman, 2014

f. Ve

r�ca

l G

arde

n

- Provide vegeta�ve detritus for aqua�c ecosystem - Provide aesthe�c waterfront experience

Untried; although successful terrestrial examples exist

Francis and Lorimer, 2011

196 Urban Ecosyst (2015) 18:189–208

Habitat benches

Habitat benches are piles of coarse rocky substrate constructed adjacent to seawalls to createareas of shallow water (Table 2c). The shallow water provides habitat for invertebrates, fish,and submergent and emergent vegetation (Toft et al. 2010; Toft et al. 2013). A habitat benchshould either be made of angular well-packed rock substrate or supported by large rocks toprevent substrate movement. Ongoing monitoring is recommended for habitat benches andother projects that may be susceptible to movement (Toft et al. 2008).

A habitat bench along the shoreline of the Olympic Sculpture Park in Seattle, completed in2007, reinforces an existing seawall and provides habitat functions similar to rocky shorelinesfound elsewhere in the Puget Sound. Monitoring was conducted for 1 year prior to and 5 yearsafter construction and concluded that the bench improved habitat for biota compared to theadjacent armored shorelines (Toft et al. 2013). Juvenile salmonids, forage fish (Osmeridae),and demersal fish (Cottidae) were more abundant in shallow water provided by the habitatbench and juvenile salmonids were also observed feeding. High densities (20,000 to 60,000per m2) of epibenthic invertebrates, including harpacticoid copepods and amphipods, alongwith diverse and dense stands of kelps and other algae were also observed at the habitat bench(Toft et al. 2008; Toft et al. 2012; Toft et al. 2013).

Vegetation and substrate baskets

Vegetation baskets are designed to attach to seawalls and support emergent or submergedvegetation (Table 2d). Depending on the aquatic plants selected, vegetation baskets mayprovide food, shelter, or reproductive sites for aquatic organisms, all of which are missingfrom the urban waterfront due to the loss of shallow nearshore habitat (Holloway and Connell2002; Perkol-Finkel et al. 2008).

Habitat Underwater Baskets (HUB) are vegetation baskets designed for the CuyahogaRiver near Cleveland, Ohio. Manufactured to withstand high flow conditions, the baskets

Fig. 2 Test seawall texture panels in Seattle. This photo depicts, from left to right: cobbled flat panel, cobbledfinned panel, cobbled stepped panel, smooth finned panel, and smooth flat panel. The smooth stepped panel isnot shown in the photo

Urban Ecosyst (2015) 18:189–208 197

are made of molded rubber and hold 0.4 m by 0.3 m (16in by 12in) mesh bags filled with31.8 kg (70 lb) of planting medium and 3–4 native plants. The Cuyahoga HUBs were designedto hang from the waterfront wall on a chain/brindle system in the recesses of corrugatedbulkheads, where theoretically they would be protected from ship traffic, prop wash, anddebris flow (White 2009). In 2008, approximately 200 HUBs were installed in the Cuyahogafor the intended benefit of 70 species of fish, includingmigrating fish (White and Goodman2008).

However, the first installation attempt was unsuccessful due to issues with the HUB’sattachment hardware, resulting in the HUBs becoming submerged and plants and soilwashing out. In the second attempt, the attachments held, however high water levels due toheavy rains again completely submerged the HUBs, preventing plant growth and causingheavy sedimentation of the HUB. Subsequent approaches, including floating islands andpre-seeded growing mats, also failed as the river’s energy washed plants away anddeposited sediment, submerging the products. This experience highlights the need forpilot and post occupancy studies to examine the realized ecological benefits of anyproposed ecological design.

Substrate baskets are similar to vegetation baskets; though instead of growing medium forvascular plants they contain sand or gravel substrates, or no substrate in order to mimictidepools (Table 2e). In Seattle, test substrate baskets (livestock troughs filled with differentsubstrate materials) were installed at the same time as the seawall texturing test panels. As inCleveland, wave action washed the substrate material from the substrate baskets and they wereabandoned. However, in Australia, another study added empty half-round flowerpots to theseawall to mimic tide pools. This proved a successful, cost-effective measure that increased thenumber of species present, increased cover and density of algae and invertebrates, andbenefitted the mobile species most affected by replacing rocky shorelines with seawalls(Browne and Chapman 2011; Browne and Chapman 2014).

While more ecological infrastructure designs exist for seawalls (Table 2f), there aresignificant opportunities for urban designers to improve and expand on these designs. Oneparticular area in need of attention are designs incorporating shoreline vegetation. Shorelinearmoring also eliminates shoreline vegetation, an ecologically important link between terres-trial and aquatic ecosystems (Toft et al. 2004; Toft and Cordell 2006).

Docks, piers, and overwater structures

Ecological designs for docks, piers, and overwater structures must address shading impactsand should consider habitat structure and the impact of pilings and pontoons on communitycomposition. To date, implemented ecological infrastructure projects have focused on theeffects of shading (Table 3).

The orientation of the dock and spacing of pilings can be engineered to promote lightpenetration under the dock (Fig. 3). This may also reduce the impact of dock pilings on waterflow patterns. In addition, there are commercial products available that are designed to reflectlight under or let light pass through docks, and metal or fiberglass grating installed on theperimeter of a dock can soften the light/dark boundary (Table 3a; Blanton et al. 2002; Shaferand Robinson 2001). Different approaches are needed based on the target organism, asencouraging fish passage requires lower light levels than photosynthesis. Recent projects inWashington are using or testing these approaches, including the Port Townsend NorthwestMaritime Center dock built in 2009 using grating and reflective panels to support eelgrass andthe 2013 installation of test glass panels in Pier 62/63 in Seattle to encourage fish passage.However, other research has found that alternative decking materials do not adequately

198 Urban Ecosyst (2015) 18:189–208

mitigate the impacts of shading, and dock orientation and height are more important(Alexander 2012).

Ecological designs that address habitat structure still need to be developed. Safety inspec-tions make retrofitting structural pilings difficult, so habitat structure needs to be consideredduring the design phase. One option is to incorporate textured pilings into dock design to

Fig. 3 Piling configurations on Seattle’s urban waterfront: a dense wood pilings; b new concrete pilings allowmore space between pilings; c dock with old pilings with little light penetration under the dock and a harsh light/dark boundary; d the new Port of Seattle building, which was designed to allow more light under the dock

Table 3 Ecological designs to replace traditional docks, piers, and other overwater structures

Illustra�on Design Focus Design Successful?

Key Resources

a. In

crea

se L

igh�

ng

Belo

w D

ocks

- Increase amount of light available below docks; benefit algae, seagrass, etc.- Facilitate nursery habitat for fish and invertebrates

Maybe; Trials but no conclusive evidence. Awai�ng results of Sea�le trial launched Oct 2013.

Blanton et al., 2002

Shafer and Robinson, 2001

Alexander, 2012

b. P

iling

Hab

itat

- Increase inter�dal habitat area to benefit fish, vegeta�on, etc.- Provide/ reconstruct rocky habitat for fish/marine organisms

Untried; although successful ar�ficial reef examples exist.

None in published literature.

Urban Ecosyst (2015) 18:189–208 199

create more surface area for algae, barnacles, and other marine organisms to grow.Benthic habitat, possibly in the form of artificial reefs, could potentially be incorpo-rated into the base of pilings to provide shelter for fish and other organisms feedingon algae and invertebrates inhabiting the pilings (Table 3b; Alevras 2010). However,additional research is needed as non-native species may unintentionally benefit fromthese types of designs. Overall, docks and overwater structures remain in need ofcreative ecological design efforts to address altered water flow, shading, and habitatstructure.

Urban benthos and water column

Docks, seawalls, and urbanization of the waterfront impact benthic habitat in ways that cannoteasily be addressed through alterations to seawall and dock design. However, benthic habitatenhancement addressing the loss of hard or soft substrate and benthic vegetation in the urbanwaterfront may be built in conjunction with or independently of seawall and dock development(Table 4).

Submerged breakwater

In areas where seawalls have caused scouring, submerged breakwaters built in front ofseawalls can mitigate wave energy and create protected soft substrate habitat suitable foralgae, small invertebrates, and juvenile fish (Table 4a; Hasegawa and Shimizu 1995; Takakiet al. 1995). In Japan, submerged breakwaters built in front of emergent breakwaters are used

Table 4 Ecological designs for the urban benthos and water column

Illustra�on Design Focus Design Successful?

Key Resources

a. S

ubm

erge

d Br

eakw

ater

- Create so� sediment areas of shallow and calm water- Extend the life of seawalls

Yes; Japan Akeda et al., 1995

Yano et al., 1995

b. A

r�fic

ial R

eefs

- Provide/ reconstruct rocky habitat for fish/marine organisms

Yes; West Harlem, New York City

None in publishedliterature.

c. A

r�fic

ial R

eefs

(A

lgae

)

- Provide/reconstruct rocky habitat as basis for algae - Support ecosystem reliant on algae (fish, invertebrates, etc).

Yes; Japan and California

Terawaki et al., 2001

Deysher,et al., 2002

d. R

ocky

O

utcr

oppi

ng

- Increase inter�dal habitat area; - Reintroduce shallow water habitat for the benefit fish, vegeta�on, etc.- Provide unique waterfront aesthe�c experience

Yes; Habitat Island, Southeast False Creek, Vancouver, B.C.

None in published literature,but see Johnson 1991.

200 Urban Ecosyst (2015) 18:189–208

to protect existing kelp beds, create new kelp beds, and create a protected zone for sea urchins,juvenile fish, and other organisms, while also protecting investment in infrastructure byincreasing the lifespan of shoreline armoring. Follow up ecological research found that thecommunity composition approached that of natural rocky reefs after 10 years (Akeda et al.1995; Yano et al. 1995). Artificial reefs have also been used as submerged breakwaters tocreate soft substrate habitat (Harris 2004).

Artificial reefs

Designs that improve the quality of rocky substrate benthic habitat draw heavily fromthe artificial reef literature (e.g. Deysher et al. 2002; Kennish et al. 2002; Seaman2007). Despite the ongoing debate over fish attraction vs. production, infrastructurespecifically designed for biodiversity and appropriate for local fish species is morelikely to be successful (Table 4b; Pickering and Whitmarsh 1997). In New York City,an artificial reef project offshore of the West Harlem Waterfront Park was installed toreintegrate the rocky benthic habitat historically present around the island ofManhattan and currently covered in deep sediment deposits. Prior to installation, adultfish were not present due to inadequate habitat structure. In response, 40 cobbledReefBall™ units were installed on pilings along the West Harlem waterfront, in apattern designed to avoid further sedimentation. ReefBalls™ are hollow, textured,perforated concrete domes that have been used to replicate rocky benthic habitat(Table 4b). Subsequent monitoring indicates that despite some minor ice damage,the reef installation is successfully attracting fish, including juvenile striped bass(Morone saxatilis), crabs, and other species (Alevras 2010).

Similar structures designed to support algae growth instead of fish include low profilestructures made of local rock or concrete to accommodate algae holdfasts. Successful designsprovide habitat similar to natural algae beds by incorporating local species habitat require-ments in their design (Table 4c; Choi et al. 2002; Deysher et al. 2002; Falace et al. 2006; Ohgaiet al. 1995; Somsueb et al. 2001; Terawaki et al. 2001; Yokouchi et al. 1991). This type ofecological infrastructure is popular in Japan where it is used in commercial and fishing portconstruction (Isobe 1998; Terawaki et al. 2001).

Rock outcroppings

Rock outcroppings provide shallow water habitat area, microhabitat, and places for water birdsto nest (Table 4d). In Vancouver, B.C., an artificial rocky island named Habitat Island wasconstructed using cobble substrate as compensatory fish habitat for the Olympic Villagedevelopment in Southeast False Creek. This installation created rocky benthic habitat and amore complex shoreline than was previously present. Subsequent monitoring efforts conduct-ed by Golder Associates found no sloughing or erosion of the installed substrates, multiple fishspecies utilizing the site (including Oncorhynchus sp.), and continued colonization of macro-algae and sessile invertebrates.

Summary

The review of literature and design examples provide evidence that integrating ecologicalinfrastructure strategies in the urban waterfront—whether through new installation or modifi-cation to existing structures—can improve the quality of urban ecosystem functioning andservice provision (Bulleri and Airoldi 2005; Connell 2001; Glasby et al. 2007; Salomidi et al.

Urban Ecosyst (2015) 18:189–208 201

2013; Simkanin et al. 2012). Urban areas are important for conservation and urban designersand planners should try to encourage the biogeochemical conditions that favor species andecosystem services of interest—even though urban systems are structured and function innovel ways as compared to less disturbed settings and ecological design strategies will notlikely be able to return a system to its historical state (Kowarik 2011; Seastedt et al. 2008).Design processes should focus on a net-positive approach to support ecosystem services whichare contingent on the provision of habitat (Fig. 4; Mapes and Wolch 2011).

Conclusions

Design strategies for ecological infrastructure to improve the quality of urban ecosystemfunction and service provision are still maturing. Currently, most research focuses on thedifferences between conventional aquatic infrastructure and rocky habitat (e.g. Bulleri et al.2004; Chapman 2006) and additional work is needed to examine other environments such asmangroves and salt marshes, and test design strategies for these locations. Research at bothinfrastructure and waterfront scales needs to address ecological processes, rather than continueto focus on changes in ecological structure (Chapman and Underwood 2011; though see Ivesaet al. 2010 and Klein et al. 2011). Processes and outcomes on built structures can onlysometimes be predicted based on known ecology (Klein et al. 2011; Perkol-Finkel et al.2012). Further, little is understood about the emergent properties (patterns and processes) ofmultiple infrastructure types in the urbanized waterfront (including ecological and conven-tional designs) or how species traverse and disperse along the urban waterfront (Williams et al.2013). Understanding the contributing factors of poor ecosystem function at different spatialand temporal scales will help to design and build infrastructure that successfully supportsecosystem processes, function and services, to supplement the current focus on ecologicalstructure (Forsyth 2007; Pioch et al. 2011; Perkol-Finkel et al. 2012; Riley 1998; Toft et al.2010; Toft et al. 2013). Executing this research would also provide baseline information onlocal ecological communities from which urban designers, planners and ecologists could formclear project objectives and design goals (Chapman 2011).

To build on current examples of ecological infrastructure, future research should alsoevaluate design concepts. Scientific research and monitoring programs are valuable: 1) priorto the implementation of ecological infrastructure to help define project goals, 2) during designof ecological infrastructure to test design variants and increase the likelihood of project

Fig. 4 Aggressive installation of ecological infrastructure designs may work together to provide habitat. Here, adock designed to reduce shading impacts has been outfitted with habitat integrated into the dock pilings,including fluting along the piling and artificial reef units placed at the base. A nearby breakwater has created acalm area and some valuable soft sediment habitat. Reef fish occupying the artificial reef units at the base of thepilings can forage on the sand infauna, and juvenile fish and other organisms can find shelter in the area of calmwater created by the breakwater

202 Urban Ecosyst (2015) 18:189–208

success, and 3) after completion of an ecological infrastructure installation to documentperformance and provide critical feedback for management (Chapman 2011; Chapman andUnderwood 2011; Cordell 2011; Morrissey et al. 2012; Toft et al. 2012). Yet, few studiesattempt to test design ideas for aquatic ecological infrastructure in situ, and fewer still reporttheir results. Notable exceptions include the extensive pre-construction experimentation for theseawall panels in Seattle (Goff 2008, 2010) and the work with artificial micro-crevices,fractures, and tidepools (Moschella et al. 2005).

Additionally, infrastructure management and maintenance—an important long termcomponent of aquatic infrastructure—is not well understood (Hostetler 2012).Maintenance can remove dominant species (including mussels and oysters) to thebenefit of fast growing opportunistic species, creating shifts in community composi-tion (Airoldi and Bulleri 2011). The design of ecological aquatic infrastructure cannotbe complete without a maintenance and management regime that will maximize the benefits totarget species.

Yet even with this research, global climate change—including the effects of sea level rise,sea surface warming and ocean acidification—will create additional challenges. Anticipatingtrends and designing for species that may use the infrastructure over the course of its life cycleis an important but challenging goal. For example, planners must anticipate local impacts ofsea level rise to design infrastructure that will be effective over a range of climate scenarios(e.g. seawalls that will continue to protect a city for 100 years) and concurrent shifts inorganisms’ range (tidal elevation and water temperature). Increasing sea surface temperaturesmakes installing ecological infrastructure more critical for connectivity as species migrate inresponse to changes in water temperature. Upgrading waterfront infrastructure to accommo-date sea level rise, replace aging or failing infrastructure, or converting industrial infrastructureto public use provide opportunities for cost-effectively replacing conventional infrastructurewith ecological infrastructure.

Acknowledgments Ourmost sincere gratitude to all thosewho took the time to speakwith us about their ecologicaldesign projects. Thank you to Martha Groom, Dan Huppert, Amber Moore, Gordon Bradley, and the anonymousreviewers for their insightful comments and constructive criticism on earlier drafts of this manuscript.

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