Reefs and islands of the Chagos Archipelago, Indian Ocean: why itis the world’s largest no-take marine protected area

C. R. C. SHEPPARDa,*, M. ATEWEBERHANa, B. W. BOWENb, P. CARRc, C. A. CHENd, C. CLUBBEe, M. T. CRAIGf,R. EBINGHAUSg, J. EBLEb, N. FITZSIMMONSh, M. R. GAITHERb, C-H. GANd, M. GOLLOCKi, N. GUZMANj,

N. A. J. GRAHAMk, A. HARRISa, R. JONESi, S. KESHAVMURTHYd, H. KOLDEWEYi, C. G. LUNDINl, J. A.MORTIMERm,D. OBURAn, M. PFEIFFERo, A. R. G. PRICEa, S. PURKISp, P. RAINESq, J. W. READMANr, B. RIEGLp, A. ROGERSs,

M. SCHLEYERt, M. R. D SEAWARDu, A. L. S. SHEPPARDa, J. TAMELANDERv, J. R. TURNERw, S. VISRAMd,C. VOGLERx, S. VOGTy, H. WOLSCHKEg, J. M-C. YANGd, S-Y. YANGd and C. YESSONi

aSchool of Life Sciences, University of Warwick, CV4 7AL, UKbHawai’i Institute of Marine Biology, P.O. Box 1346, Kane’ohe, Hawai’i. 96744, USA

cBF BIOT, Diego Garcia, BIOT, BFPO 485, UKdBiodiversity Research Centre, Academia Sinica, 128 Academia Road, Nankang, Taipei, 115, Taiwan

eRoyal Botanic Gardens Kew, Richmond, Surrey TW9 3AB, UKfDepartment of Marine Sciences, University of Puerto Rico, Mayaguez, P.O. Box 9000, Mayaguez, PR 00681

gDepartment for Environmental Chemistry, Helmholtz-Zentrum Geesthacht, Zentrum für Material- und Küstenforschung GmbH,Max-Planck-Straße 1 I 21502, Geesthacht I, Germany

hInstitute for Applied Ecology, University of Canberra, ACT 2601, AustraliaiZoological Society of London, Regents Park, London, NW1 4RY, UK

jNestor Guzman: NAVFACFE PWD DG Environmental, PSC 466 Box 5, FPO AP, 96595-0005kARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia

lIUCN Marine Programme, Rue Mauverney 28, Gland, 1196, SwitzerlandmDepartment of Biology, University of Florida, Gainesville, Florida, USA

nCORDIO East Africa, #9 Kibaki Flats, Kenyatta Beach, Bamburi Beach, P.O.BOX 10135, Mombasa 80101, KenyaoRWTH Aachen University, Templergraben 55, 52056 Aachen, Germany

pNational Coral Reef Institute, Nova Southeastern University, Oceanographic Center, 8000 North Ocean Drive, Dania Beach, FL33004, USA

qCoral Cay Conservation, Elizabeth House, 39 York Road, London SE1 7NQ, UKrPlymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH, UK

sDepartment of Zoology, University of Oxford, The Tinbergen Building, South Parks Road, Oxford, OX1 3PS, UKtOceanographic Research Institute, PO Box 10712, Marine Parade, Durban, 4056, South Africa

uDivision of Archaeological, Geographical and Environmental Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, UKvUNEP Division of Environmental Policy Implementation, UN, Rajdamnern Nok Av., Bangkok, 10200, Thailand

wSchool of Ocean Sciences, Bangor University, Menai Bridge, Anglesey, LL59 5AB, UKxDepartment für Geo- und Umweltwissenschaften Paläontologie & Geobiologie, Ludwig- Maximilians-Universität, Richard-Wagner-Str.

10, 80333, München, GermanyyNaval Facilities Engineering Command Far East, PSC 473, Box 1, FPO AP 96349, USA

ABSTRACT

1. The Chagos Archipelago was designated a no-take marine protected area (MPA) in 2010; it covers 550 000km2,with more than 60 000km2 shallow limestone platform and reefs. This has doubled the global cover of such MPAs.

2. It contains 25–50% of the Indian Ocean reef area remaining in excellent condition, as well as the world’slargest contiguous undamaged reef area. It has suffered from warming episodes, but after the most severe mortalityevent of 1998, coral cover was restored after 10 years.

*Correspondence to: C. R. C. Sheppard, School of Life Sciences, University of Warwick, CV4 7AL, UK. E-mail: charles.sheppard@warwick.ac.uk

Copyright # 2012 John Wiley & Sons, Ltd.

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS

Aquatic Conserv: Mar. Freshw. Ecosyst. 22: 232–261 (2012)

Published online 17 January 2012 in Wiley Online Library(wileyonlinelibrary.com). DOI: 10.1002/aqc.1248

3. Coral reef fishes are orders of magnitude more abundant than in other Indian Ocean locations, regardless ofwhether the latter are fished or protected.

4. Coral diseases are extremely low, and no invasive marine species are known.5. Genetically, Chagos marine species are part of the Western Indian Ocean, and Chagos serves as a

‘stepping-stone’ in the ocean.6. The no-take MPA extends to the 200 nm boundary, and. includes 86 unfished seamounts and 243 deep knolls

as well as encompassing important pelagic species.7. On the larger islands, native plants, coconut crabs, bird and turtle colonies were largely destroyed in

plantation times, but several smaller islands are in relatively undamaged state.8. There are now 10 ‘important bird areas’, coconut crab density is high and numbers of green and hawksbill

turtles are recovering.9. Diego Garcia atoll contains a military facility; this atoll contains one Ramsar site and several ‘strict nature

reserves’. Pollutant monitoring shows it to be the least polluted inhabited atoll in the world. Today, strictenvironmental regulations are enforced.

10. Shoreline erosion is significant in many places. Its economic cost in the inhabited part of Diego Garcia isvery high, but all islands are vulnerable.

11. Chagos is ideally situated for several monitoring programmes, and use is increasingly being made of thearchipelago for this purpose.Copyright # 2012 John Wiley & Sons, Ltd.

Received 4 August 2011; Revised 31 October 2011; Accepted 14 November 2011

KEY WORDS: Chagos; British Indian Ocean Territory; marine protected area; coral recovery; reef fishes; seamounts; reef disease;marine invasives; fisheries; island conservation

INTRODUCTION

This paper reviews the scientific work and historicinformation that demonstrates the outstandingecological values of the Chagos Archipelago,which led in 2010 to the creation of the world’slargest marine protected area (MPA), and whichbecame fully a no-take MPA later the same year.The archipelago (Figure 1) forms the BritishIndian Ocean Territory (BIOT), created in 1965for UK and USA defence purposes. It is a largegroup of atolls and submerged banks in the centralIndian Ocean, lying at the southernmost end of theLakshadweep–Maldives–Chagos ridge. Its central200� 300 km area contains five atolls with islands,one atoll which is awash at high tide, and a dozenmore which are submerged to depths of 6–25m.The Great Chagos Bank is the world’s largest atollin area, although it contains only eight islands onits western and northern rim. The area within thetotal BIOT 200 nm zone is about 550 000km2.

During recent decades, most of the tropicalocean has been heavily affected by pollution,over-exploitation and various unwise forms ofdevelopment (Millennium Ecosystem Assessment,2005). Almost all indicators of ‘ocean health’continue to show worsening trajectories, andmany attempted remedial measures have failedto arrest the decline of habitats and ecosystems

essential for both human welfare and maintenanceof biodiversity and productivity. The world’s oceansare affected by overfishing, pollution, agricultureand industry, shoreline construction, and climatechange (Jackson et al., 2001). Coral reefs inparticular are overexploited because they supportgrowing populations of some of the world’s poorestpeople (Wilkinson, 2008a; Burke et al., 2011). Allreefs are highly vulnerable to increasing intensityof human exploitation, which reduces both biomassand productivity, and consequences of reefdeterioration may be greater than previouslyanticipated (Mora et al., 2011). Most conventionalforms of marine management are failing to arrestthe decline, so many marine science bodies,conservation organizations and internationalconventions have called for more and larger marineprotected areas (MPAs) that have effective levels ofprotection (United Nations, 2002; Wood et al.,2008; Nelson and Bradner, 2010). MPAs remainone of the only extensive tools being used directlyfor conservation purposes (Spalding et al., 2010).

A recent assessment (Toropova et al., 2010)showed that there are about 5900 MPAs, covering4.2 million km2, which covers only 1.17% of theoceans. Recently their median size was only 5 km2

(Wood et al., 2008). The small proportion of oceancovered by MPAs must be compared with estimated

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need. The Convention on Biological Diversity calledinitially for 10% of the world’s EEZ to be protectedby some form of MPA by 2010, though the targetdate was later put back to 2020. The World ParksCongress called for 20% of the oceans to be protectedby 2012, and the World Summit on SustainableDevelopment called for a global network ofcomprehensive, representative and effectivelymanaged MPAs by 2012 (United Nations, 2002).In developed countries of the Atlantic, theOSPAR Commission called for an ecologicallycoherent, well managed network of MPAs alsoby 2012. Most targets will manifestly fail, andparticipating parties would need to create over19 million of the median size MPAs to achievethese targets. In 2010, 260 marine scientists madean urgent call for more and larger MPAs (http://www.globaloceanlegacy.org/), and a figure of 30%(not 10–20%) has increasingly emerged as the areaneeded to avert permanent damage.

Unfortunately, the meaning of ‘protected’ varieswidely, with most allowing only partial protection

and many also allowing fishing (one of the mostecosystem distorting activities), while many lack anyprotection at all. The latter are commonly called‘paper parks’ and, regrettably, human pressures makethis category the large majority. For coral reefs, only6% are effectively managed, 21% are ineffectivelymanaged, and 73% lie outside any MPA (Burkeet al., 2011). Reasons for MPA failures range frombeing declared solely to meet ‘targets’ which are theninadequately resourced, to being simply overwhelmedby close proximity to large human populations.

Chagos and the marine protected area

Chagos was occupied from the 18th century, duringwhich time most of its native vegetation wasconverted to coconut plantations. This industrylasted until the 1970s. Two of the five atolls wereabandoned for economic reasons and social problemsin the 1930s, and in the early 1970s the plantations onthe remaining three atolls were closed due to theestablishment of a military facility. The peoplewere moved to various countries, notably Mauritiusand the Seychelles, and some eventually to Europe,especially England (Edis, 2004). The remainingplantations were already in some decline givendiminishing world demand for coconuts and theascendency of palm oil from elsewhere, butnevertheless political issues surrounding theforced removal of the last inhabitants has been miredin controversy ever since. For the last 40 years theislands have been uninhabited except for thesouthernmost atoll of Diego Garcia, the westernarm of which contains the military facility and atleast 1000 Asian contractors and others. Thatfacility does not depend on local food resourcesbut is provisioned and supported entirely fromoutside the archipelago.

Over the period of BIOT’s existence, there havebeen a dozen scientific visits, involving more than50 visiting scientists. It has become clear during thisperiod when coral reefs in most of the Indian Oceanhave become seriously degraded that those ofChagos persist in an exceptionally good state. Thisled increasingly to calls to extend its conservation,and data to support the concept came from over200 papers arising from both those scientificexpeditions and, to a lesser extent, from unpublishedinformation, from regional data and from modelling.

Recently, the Pew Ocean Legacy Programincluded Chagos as one of five areas selected forprotection, and promoted efforts to convince theUK Government to declare it a no-take MPA to

Peros Banhos atoll

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Figure 1. The Chagos Archipelago. Inset shows location and MPAboundary (circular shape with flattened northern border). Main map:the five atolls with land are shown in bold, the islands on Great ChagosBank and submerged reefs and atolls are not bold. All are located in the

central area of the MPA.

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the 200 nm boundary (Nelson and Bradner, 2010).Part of this process was the creation of the ChagosEnvironment Network (CEN), a loose associationof several leading UK science bodies and NGOs,whose role was to support efforts to ensure thatChagos’ globally important natural environmentwould be conserved as a unique and valuableresource for present and future generations. In2010, CEN responded to the UK Government’sConsultation, saying that only designation as ano-take MPA ‘. . . guarantees full protection for theecosystems and species of the Chagos Archipelagoand its surrounding reefs, lagoons and waters. Only[this] provides the complete protection needed tounderpin the Chagos Protected Area’s value asan important global reference site for a wide rangeof scientific ecological, oceanographic and climatestudies, as well as its continued benefits to humansinto the future’ (CEN, 2010).

BIOT is a UK Overseas Territory and as suchhas its own government, which in this case is theoffice of the BIOT Administration located in theUK Foreign and Commonwealth Office in London.The senior UK military officer in the archipelago isthe British Representative of the Commissioner.The UK Foreign Secretary announced the creationof BIOT as a no-take MPA, instructing theCommissioner to declare it as such in April 2010(http://www.fco.gov.uk/en/news/latest-news/?view=News&id=22014096). The Commissioner,in ProclamationNumber 1 of 2010, proclaimed it such

‘in the name of the Queen’. Existing environmentallaws are currently being revised and consolidated toaccommodate this status. Diego Garcia atoll to its3 nm boundary is excluded from the MPA. Thearea thus excluded is less than 1% of the totalarea although it has several pre-existing, strictenvironmental laws of its own, and contains aRamsar site (see later). Existing tuna fishing licenceswere discontinued, and the deficit for BIOTfinances of approximately $1 million per year wassubsequently replaced from private sources. Itis currently the largest MPA in the world(Nelson and Bradner, 2010) and is now also partof the ‘Big Ocean Network’, an informationexchange network of managers and partners ofexisting and proposed large-scale marine managedareas (www.bigoceanmanagers.org/). Monitoringand enforcement are undertaken in large partby a patrol vessel which serves as a mobile basefor both the military and civilian researchexpeditions.

Island and reef areas

Figure 2(a) shows the areas of islands and reefs.Diego Garcia contains half the total land area, therest being split among over 50 small islands, thenumber varying to some degree with tidal heightand shifts of sand banks. All islands are verylow lying, and are typical coral cays constructedof limestone. Beneath these lie freshwater lensessustained by high rainfall.

Figure 2. a) island areas in the Chagos Archipelago (scale in ha). The largest islands are named. b) area of submerged substrate in the archipelago(scale in km2) (from Dumbraveanu and Sheppard, 1999).

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In contrast to the small island areas, sublittoralsubstrate in the photic zone is calculated to beapproximately 60 000km2 (Figure 2(b)) (Dumbraveanuand Sheppard, 1999). How much of this huge areais actively growing reef is uncertain; more than95% of the territory has never been studied, thoughsome areas are apparently eroding and otherssupport sand and/or large seagrass beds. There isenormous opportunity for new discoveries: asrecently as 2010 an expedition discovered manyhectares of seagrass and a previously unknown3 km2 mangrove forest. Other parts of Chagoshave been mapped using bathymetric or satellitedata-based modelling (Yesson et al., 2011, see laterFigures 9 and S12 in Supplementary Material).

REEF CONDITION

Coral cover and changes due to mortality episodes

There were no quantitative studies of reef conditionon Chagos reefs before the 1970s, althoughdescriptive studies, notably Stoddart and Taylor(1971), described land and reef flat in DiegoGarcia. From the 1970s, episodic visits enabled aseries of coral cover measurements to be takenon reef slopes.

Coral cover declined between the first surveyin 1978 (Sheppard, 1980a) and the next in 1996(Sheppard, 1999a) (Figure 3). This was mainly dueto loss of shallow and mid-depth branching species,particularly Acropora palifera and table coralsincluding Acropora cytherea, and causes were onlyspeculated upon at the time (Sheppard, 1999a).Later, after much work globally and more surveysin Chagos, the cause was suggested to be severalwarming events. This modest decline occurred inmany Indian Ocean islands groups over this period

(Ateweberhan et al., 2011) and in Kenya (Muthigaet al., 2008) though it was not universal.

Severe warming in 1998 then caused severemortality on all Chagos reefs (Sheppard, 1999b;Sheppard et al., 2002; Figures 3 and S1 inSupplementary Material) as it did throughout theIndian Ocean (Ateweberhan et al., 2011). Coraland soft coral mortality was almost total on severalChagos ocean-facing reefs to clearly defineddepths, below which corals provided much highercover. This killed zone extended deeper in southernatolls, and in Diego Garcia for example wasgreater than 40m depth, while in more northernatolls it extended to only about 10–15m depth(Sheppard et al., 2002). Such variability was mirroredin the Indian Ocean as a whole (Sheppard, 2006).Lagoon reefs of Chagos atolls were much lessaffected than ocean facing reefs (Figure S1 inSupplementary Material), with many retaininghigh coral cover, including stands of Acropora.Post-1998, coral species diversity was greatest in deeplagoon areas.

Coral recovery

Several ocean-facing transects around the atollshave been monitored repeatedly from 1999 onwards(Figure 4). On these, no increase of hard coral coverwas seen for 3 years following the mortality,although by 2001 large numbers of juveniles werepresent, at densities of up to 28m-2, the highestrecorded globally at that time (Sheppard et al., 2002;Harris and Sheppard, 2008). Coral spat provided 6%cover on easily measured (but disintegrating) deadcoral tables, with a further 5% cover provided byjuvenile soft corals, indicating good recoverypotential (Figure S2 in Supplementary Material).Increase in coral cover became evident by 2006,

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Figure 3. Percentage coral on reefs by the main coral types in 4 years, for the major live categories identifiable by snorkelling in 1999. Arrows along thetop are dates and approximate relative severity (arrow thickness) of previous warming events (from Sheppard, 1999a).

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especially in shallow water (Harris and Sheppard,2008; Sheppard et al., 2008) where restoration topre-1998 levels occurred by 2010. Deeper recoveryhas been slower. Coral cover in 2011 reachedvalues recorded in 1978 in a few transects in DiegoGarcia, but most atolls were not surveyed duringthat year.

In 2006, extensive video surveys were takenand archived, showing mean percentage cover ofseveral benthic categories (Bayley, 2009) (Figures 5and S3, S4 in Supplementary Material). Theseshowed no significant differences that year in hardcoral cover in pooled data between atolls, althoughsignificant differences existed at depth and site levelsbetween ocean-facing reefs. Hard coral cover was

significantly higher in lagoons (63.04� 3.19%)than ocean-facing slopes (39.69� 2.03%). Softcoral was higher on ocean-facing slopes (14.02�1.58%) than in lagoons (2.65� 0.72%). Hardcoral cover decreased between 6 and 25m, butsponge and soft corals showed an increase withdepth. Dead standing coral at most sites was lowat 3–13%, and rubble did not change significantlyat different depths. Structural complexity wasreduced to 15m in the outer atolls, and to deeperzones on the Great Chagos Bank and DiegoGarcia atoll. By 2006 all shallow regions haddeveloped sufficiently to form a canopy, withcolonies competing with one another for space(O’Farrell, 2007). Furthermore, deep lagoonalareas exhibited the highest numbers of small,juvenile coral colonies. Modelling studies indicatethat such deep reef areas could be responsible forrelatively rapid recolonization of denuded shallowreefs (Riegl and Piller, 2003).

The past decade has seen further coral bleachingevents in Chagos, in 2003, 2004, 2005, and a mildone in 2010. None were sufficient to cause massmortality, although species-specific coral mortalitywas recorded of many Acropora cytherea tables in2010 (Pratchett et al., 2010). Given that warmingepisodes sufficient to kill corals are predicted toincrease (Sheppard, 2003; Hoegh-Guldberg et al.,2007) it is likely that intermittent interruptions tocoral growth will continue. However, modelsbased on recruit availability scaled to the presentcoral cover, suggest that Chagos reefs will longbe able to withstand recurring strong mortality

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Figure 5. Mean percentage cover values of life form and substrate categories pooled from all depths and all sites for each of four atolls (GCB:GreatChagos Bank, DG: Diego Garcia, SAL: Salomon atoll, PB: Peros Banhos atoll), surveyed by video during 2006. Bars are error bars.

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events – even each decade – and still maintain highcoral cover. Significant declines in cover are expectedonly if both larval supply decreases and coralmortality events increase in intensity and frequency.

Pre- and post-1998 studies have also revealedsome changes in the soft coral component. Theprincipal octocorals before and after the 1998ENSO shared many common taxa (Reinicke andvan Ofwegen, 1999; Schleyer and Benayahu,2010), but a few discontinuities in their biodiversityindicate subtle changes in more persistent genera(Lobophytum, Sarcophyton). Some fast-growing‘fugitive’ genera (e.g. Cespitularia, Efflatounaria,Heteroxenia) disappeared after the ENSO-relatedcoral bleaching (Reinicke and van Ofwegen, 1999;Schleyer and Benayahu, 2010), suggesting thatsuch transient fugitives might be eliminated fromsoft coral communities on isolated reef systems bybleaching disturbance of this nature. Carijoa riseii,a species often considered a fouling organism, andeven an invasive in some places (Concepcion et al.,2010), was found in 2006. The observed post-ENSOrecovery gives cause for hope for soft coral survivalin the face of climate change.

Reef fish

Biomass of reef fish around the northern atolls ofChagos was quantified for the first time in 2010, usingunderwater visual census (Graham, 2010). Biomassestimates for Chagos exceed values from both fishedand protected reefs elsewhere in the region, such asKenya, Seychelles,Madagascar and even theMaldives,by several orders of magnitude (McClanahan et al.,2009; McClanahan, 2011; Graham, 2010). TheChagos biomass estimates are matched only bysome remote, unfished locations in the Pacific Ocean(Sandin et al., 2008; Williams et al., 2011).

With recent declines in coral cover globally(Ateweberhan et al., 2011) there is growing concernover impacts on reef fish assemblages (Pratchett et al.,2008). Much work has followed the 1998 bleachingevent around the world in trying to documentchanges to reef fish populations. A compilation ofshort-term impacts (<3years post-coral mortality)of coral loss on fishes indicated that species displayingpopulation declines were those that specialized oncoral for food, shelter or settlement (Wilson et al.,2006). However, subsequent studies have shown thatlonger term effects of coral loss and reef structuralcollapse on fish are much wider reaching, with a largeportion of the fish community affected, includingreductions in species richness, reduced abundance of

many groups and changes in the size structure of thecommunity (Jones et al., 2004; Graham et al., 2006,2007, 2008; Wilson et al., 2008). Reef fish surveys inChagos conducted in 1996 were repeated in 2006using identical methodology. This was part of a studyacross seven Indian Ocean nations. One of the groupsof fish most affected by coral loss is coral-feedingbutterflyfishes, but a comparison between Chagosand Seychelles demonstrated that, although bothspecialized and generalist coral feeding butterflyfishesshowed declines in abundance in the Seychellesthrough the 1998 bleaching event, there was nodetectable difference in Chagos (Graham et al., 2009a).

Across the Indian Ocean as a whole there weredeclines in fish species richness, and in the abundanceof corallivores, planktivores and small bodied fish(<20 cm maximum attainable size) (Graham et al.,2008; MacNeil and Graham, 2010) as a result of reefdegradation. In contrast, the populations of Chagosremained remarkably stable (Figure 6). Changes infish species richness for Chagos were extremely smalland either side of zero, compared with the regionaldecline. This highlights the temporal stability ofChagos fish assemblages in response to a large-scaledisturbance, despite substantial negative responseselsewhere in the ocean, and accords with findingsof Mora et al. (2011) and Sandin et al. (2008)that reef fish assemblages are very vulnerable toanthropogenic stressors.

Also of note are some different fish behavioursthat are very rarely seen elsewhere around the worldwhere human exploitation, coastal development,and other impacts have changed abundances,ecological interactions, and behaviour. One suchexample is the daytime feeding behaviour of themoray eel, Gymnothorax pictus, on shore crabs,leaping clear of the water to capture their prey(Graham et al., 2009b). Behaviours like this, and theexceptional stability and abundance of the reef fishcommunities, makeChagos a very important referencearea with which scientists can understand ecologicaland behavioural changes elsewhere in the world.

Coral diseases

In 2006 a survey assessed corals along 37 transectsat eight sites across the archipelago (Figure 7).Overall prevalence of disease was 5.2%, which sitsat the low end of the global spectrum where regionalaverages for ‘white syndrome’ alone are around 5%in parts of Australia, Palau, and East Africa, 8% inthe Philippines (Weil et al., 2002; Willis et al., 2004;Raymundo et al., 2005) up to around 13% at some

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sites in the Eastern Indian Ocean (Hobbs and Frisch,2010), and 20% in the Caribbean (Weil et al., 2006;Miller et al., 2009).

Temperature has been shown to be a key factortriggering diseases, with infection occurring rapidlyat elevated temperatures (Ben-Haim and Rosenberg,2002; Bruno et al., 2007; Harvell et al., 2007). Thusthe increasing frequency of raised temperatureepisodes gives cause for concern. Coral diseasesoften arise from changes to the normal, commensalrelationship between the coral and the bacterialcommunity in their mucus, skeleton, and tissues(Rohwer and Kelley, 2004; Lesser et al., 2007).Physiological stresses that cause corals to becomeoverwhelmed by bacteria are often anthropogenic

in origin, coming from sediment deposition, nutrientrise (Bruno et al., 2003; Kaczmarsky and Richardson,2011), or sea temperature rise (Harvell et al., 2007;Zvuloni et al., 2009). Other factors correlated withthe likelihood of coral disease include geographicalrange and predator diversity (Diaz and Madin,2011), while a higher density of individuals alsoincreases susceptibility (Willis et al., 2004; Brunoet al., 2007). Although remoteness from people isno guarantee of absence of disease, especially iftemperature rises (Williams et al., 2007), mitigationof other human induced stress factors may reducedisease prevalence (Bruno et al., 2003; Harvellet al., 2007). At present, Chagos reefs have verylow disease levels.

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Figure 7. Percentage of adult colonies in different atolls showing disease or other adverse conditions. Bars are standard error bars.

Figure 6. Change in reef fish species richness across seven countries in the Indian Ocean following the 1998 coral mortality event. Chagos sitesrepresented by filled circles. Adapted from Graham et al. (2008).

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Marine invasive species

Marine invasive alien species (IAS) are recognizedas one of the most significant threats to globalbiodiversity (Wilcove et al., 1998; Bax et al., 2010)and documented IAS are commonly significantlyunderestimated. IAS pressure is driving globaldeclines in species diversity, with the overall impactapparently increasing (McGeoch et al., 2010).Notably, over 100 introduced marine species covering14 phyla are known from ports in the Pacific (Coleset al., 1999). Article 8(h) of the Convention onBiological Diversity calls for prevention ofintroductions and control or eradication of alienspecies that threaten ecosystems, habitats orspecies, and the recently agreed Aichi BiodiversityTargets call for identifying pathways and puttingin place by 2020 measures to prevent speciesintroduction and establishment.

Ballast water and hull fouling provide the primaryvectors for marine species introduction (Cohen andCarlton, 1998; Ruiz et al., 2000; Hewitt et al., 2004).Navy and supply ships frequently arrive in DiegoGarcia, mainly from the USA, the Middle East, andSingapore, but any ships, including recreationalyachts, may carry hull fouling organisms (Bax et al.,2002). Therefore pathways for species introductionsto Chagos exist, as do preconditions for successfulestablishment (Tamelander et al., 2009). Whilemost ships arrive at Chagos loaded, some maybe empty and ballasted. Ballast water exchangeoccurs outside the lagoon and during mid-crossingin keeping with IMO ballast water managementguidelines (IMO, 2004).

A survey of non-native marine biota in Chagos wascarried out in 2006 in all atolls (Tamelander et al.,2009) based on standard port survey methods (Hewittand Martin, 2001) but with a lower sensitivity. Hardand soft substrate benthic biota were sampled at 42sites (19 sites in Diego Garcia, nine each on the GreatChagos Bank and at Peros Banhos, and five in theSalomon atoll). Twenty-four phyla were representedin 2672 samples, with four phyla (Bryozoa, Mollusca,Annelida and Porifera) each making up over 10% ofthe total number of specimens.

No non-native species were detected in thesamples, the first time such a survey has not foundspecies introduced as a result of human activities(Tamelander et al., 2009). This finding is testamentto the ecological integrity of Chagos’ marineecosystems. Shallow marine habitats are believedto be particularly vulnerable to bioinvasions whendegraded (Heywood, 1995), but ecosystem health

and high biodiversity confer higher resistance. Only16% of marine ecoregions have no reported marineinvasions, although the true figure may be lowerbecause of under-reporting (Molnar et al., 2008).

Because controlling or eradicating a marinespecies once it is established is nearly impossible(Bax et al., 2002), management must focus onprecautionary measures (Thresher and Kuris, 2004;Carlton and Ruiz, 2005). Successful preventionand management of IAS threats in Chagos is aprerequisite for effective management of the newlyestablished MPA (Pomeroy et al., 2004; Tu, 2009).Further, this needs to be devised in the broadercontext of climate change and the potentially greaterrisk of species spread and establishment that thismay bring (Bax et al., 2010; Burgiel andMuir, 2010).

Chagos reef condition in the Indian Ocean context

Most Indian Ocean reef areas are heavily exploitedand many have shown limited recovery following the1998 bleaching disturbance (Wilkinson, 2008b;Harris, 2010). Many which declined catastrophicallyin 1998 and which also suffer from local impacts havenot recovered significantly, or at all (Harris, 2010).The 1998 bleaching event is the main determinantof coral cover change in the Indian Ocean since the1970s (Ateweberhan et al., 2011), and the centralregions, which had some of the highest coral coverestimates before 1998, suffered the worst during thebleaching event. Subsequent recovery formost of thesereefs now remains below average for the region, but ofthe central Indian Ocean reefs, recovery in Chagos ishigher than elsewhere (Ateweberhan et al., 2011).

Globally, a third of reef-building corals arethreatened with extinction (Carpenter et al., 2008)and today, in the Indian Ocean, only about athird of reefs may be attributed to a ‘low threatlevel’ category (Wilkinson, 2008a, 2008b). Chagosreefs fall within this minority group and contain asubstantial proportion of reef area in very goodcondition. Reef area estimations are difficult, andhave been subject to wide variation. Spalding et al.(2001) suggested the Indian Ocean has 32 000 km2

of reefs (the Red Sea region and the Gulf regionadding 17 400 and 4200 km2 more, respectively),and, based on this, Chagos has 3770 km2 of reefs(Rajasuriya et al., 2004) meaning Chagos comprisesup to half of this ocean’s reefs in a ‘low threat level’category (Figure 8). More recent calculations bySpalding (pers. comm. and see Burke et al., 2011)resulted in a revised estimate that Chagos provides25% of reefs in the ‘low threat’ category. Even

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this ‘. . .25% of the region’s low threat reefs is still anextraordinary proportion, and it is also worthstressing that in addition to this, these are by farthe largest contiguous reef tracts considered to beunder low threat’ (Spalding pers. comm., 2011).

While both area values are much less than the areaof illuminated shallow limestone substrate whichwas calculated from detailed bathymetric plotting(Figure 2), the values used have the importantbenefit that they were calculated consistentlythroughout the world, thus permitting comparisons;direct measurements based on bathymetry do not yethave a counterpart in most other countries.

For other Indian Ocean areas, Tamelander andRajasuriya (2008) report that ‘recovery of SouthAsian coral reefs since the 1998 mass bleachinghas been patchy; Chagos has shown particularlygood recovery, reefs in the western atoll chain ofthe Maldives and Bar Reef in Sri Lanka have alsorecovered relatively well, while many reefs near SriLanka and reefs in the eastern atoll chain of theMaldives have shown little or no recovery. . . Corallarval recruitment was very strong, such that thelowest Chagos recruit densities were at least 10times higher than rates of recruitment at mostother reefs in the central and western Indian Ocean.’For island archipelagos further west, Wilkinson(2008a) reported that ‘some reefs of the Seychellesand Comoros that suffered major damage in 1998have probably regained about half the lost coralcover; there has also been virtually no recovery onothers’. Numerous other compilations (Wilkinson,2008a; Burke et al., 2011) report patchy or poor coralrecovery in most other parts of the region.

Reasons for the good condition of Chagos reefsare likely to include remoteness from compounding

human activities, but some additional factors maycontribute. Strong light adapted ‘Clade A’ forms ofsymbiotic zooxanthellae have been identified inshallow corals in Chagos, occurring in approximatelyhalf of the shallow water Acropora colonies that wereheavily affected by warming but which are nowrecovering strongly (Yang et al., 2012; Figure S5in Supplementary Material). Also, an array oftemperature sensors at different depths has identifiedregular incursions of deep, cool water that rise tocover reefs, including during the annual periods ofgreatest warming (Sheppard, 2009).

But it is increasingly understood that direct humanpressures are the main cause of reef degradation andthis has often been underestimated in the past (Moraet al., 2011). Such activities impede recovery, andabsence of herbivore extraction, pollution, andsedimentation increase reef resilience (Hughes et al.,2010). Most of Chagos has no human populationat all. Diego Garcia imports all its requirementsand for the last 15 years at least has had strongenvironmental management. Lack of humanpressures is likely to be one major reason for thepresent good condition of these reefs.

In the Indian Ocean as a whole, direct humanpressures can only increase further. Of thisregion, a decade ago Spalding et al. (2001) noted:‘Human populations . . . are rapidly increasing.Most of the coastal populations are very poor,and heavily dependent on the adjacent reefs forfood. Unfortunately there is little control over theutilization of these resources, either throughtraditional or formal management regimes, andlarge areas of reefs have been degraded throughoverfishing or destructive fishing techniques.’ Withannual population growth rates of 2.5% beingcommon in the region, compounded by migrationto the coast in some countries that have experiencedwars or drought, coastal populations and exploitationof reefs have increased substantially since Spalding’s(2001) account. As reefs degrade, the proportion ofhealthy reefs of the Indian Ocean contained inChagos, already very high, continues to increase,so that a precautionary approach to their protectionis merited.

DEEP-WATER ECOSYSTEMS

Yesson et al. (2011) determined that 86 seamounts(conical topographic rises >1000m elevation) and243 knolls (conical topographic rises of elevation200–999m) are predicted to occur within the

Effectively Lost Reefs(%)

Reefs at Critical Stage(%)

Reefs at ThreatenedStage (%)

Reefs at Low Threatlevel (%)

Chagos

Figure 8. Percentage of reefs in different categories in the Indian Ocean.Categories are those from Wilkinson (2008a). The probable proportionoccupied by Chagos (solid line to vertical) is about half of the reefs inthe ‘best’ category. From the dashed line to vertical is an alternativeestimate of the proportion of Chagos reefs according to Spalding using

slightly different categories (pers. comm.).

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Chagos MPA (Figure 9). Chagos thus containsmore than 10% of all Indian Ocean seamountsand so the area is regionally important for thesefeatures as well. Given that globally only 506seamounts and 606 knolls lie in protected areas(Yesson et al., 2011, based on the world databaseof protected areas 2009), this means that theChagos MPA increased the world’s protection ofseamounts by 17% and knolls by 40%. Previousemphasis of the Chagos MPA has been onshallow-water ecosystems, but protection of itsseamounts is also important, especially consideringtheir high biodiversity, often representing entirelyunique ecosystems (Clark et al., 2006). Althoughthe geology of some of the seamounts and ridgesin the Indian Ocean has been explored, includingthe Chagos-Laccadives Ridge, seamount fauna ispoorly known (Rogers et al., 2007). Some data onfish exist, mainly resulting from exploratory orcommercial fishing, but no specific informationrelates to the Chagos-Laccadive Ridge. Recentmodelling studies based on 30-arc second satellitebathymetry data indicate that the Indian Oceanhosts fewer seamounts than the Atlantic and PacificOceans (Yesson et al., 2011), and many areassociated with ridges or originate at ridges.

The Indian Ocean suffers increasing pressurefrom deep-sea fishing that threatens both seamountsand other benthic habitats. The fact that there hasnever been deep-water fishing or trawling in Chagosmakes it particularly important when considered ina regional context. Deep-sea fishing in the IndianOcean was mostly undertaken by distant-waterfleets, particularly from the USSR. These fisheriestargeted redbait (Emmelichthys nitidus) and rubyfish(Plagiogeneion rubiginosus) with catches peakingabout 1980 and then decreasing to the mid-1980s(Clark et al., 2007). Fishing then switched to

alfonsino (Beryx splendens) in the 1990s as newseamounts were exploited. Some exploratorytrawling was also carried out on the MadagascarRidge and South-west Indian Ocean Ridge by Frenchvessels in the 1970s and 1980s, particularly targetingWalter’s Shoals and Sapmer Bank (Collette andParin, 1991). In the late 1990s, a new fisherydeveloped on the South-west Indian Ocean Ridgewith trawlers targeting deep-water species suchas orange roughy (Hoplostethus atlanticus), blackcardinal fish (Epigonus telescopus), southernboarfish (Pseudopentaceros richardsoni), oreo(Oreosomatidae) and alfonsino (Clark et al., 2007).This fishery rapidly expanded, with estimated catchesof orange roughy being approximately 10 000 tonnes,until the fishery collapsed. Fishing then shifted tothe Madagascar Plateau, Mozambique Ridge, andMid-Indian Ocean Ridge, targeting alfonsino andrubyfish (Clark et al., 2007). Most of these areastherefore have probably been significantly affectedby past deep-sea bottom fisheries.

Deep-sea fishing in most of the Indian Ocean iscontinuing and showing signs of increasing itsgeographic spread, mainly targeting orange roughyand alfonsino. Recent fishing has also taken placeon the Broken Ridge (eastern Indian Ocean), 90 EastRidge, possibly the Central Indian Ridge, theMozambique Ridge and Plateau and Walter’s Shoal(western Indian Ocean), where a deep-water fisheryfor lobster (Palinurus barbarae) has developed(Bensch et al., 2008). The banks around Mauritiusand high seas portions of the Saya da Malha Bankhave been targeted by fisheries for Lutjanus spp.,and lethrinid fish (SWIOFC, 2009), and there are alsoreports of unregulated gillnet fishing in the SouthernIndian Ocean such as at Walter’s Shoal, which targetsharks (Shotton, 2006). Currently, there is little or noinformation available on impacts of deep-sea fishingin high seas areas of the Indian Ocean on populationsof target or by-catch species, or on seabed ecosystems.Reporting of data is complicated by issuesof commercial confidentiality in fisheries whereindividual stocks may be located across a wide area(e.g. the South-west Indian Ocean Ridge), and thereis no adequate regional fisheries management body(see below). At present, new fisheries are developingin the region with no apparent assessment of resourcesize or appropriate exploitation levels to ensuresustainability of fisheries, or to estimate impacts ofsuch fisheries on vulnerable marine ecosystems.

Global modelling studies are currently also beingundertaken of habitat suitability for deep-seaScleractinia and Octocorallia, at 30-arc second

Figure 9. Seamounts of the Chagos MPA as identified in Yesson et al.(2011). Bathymetry data from shuttle radar topography mission 30

arc-second grid (http://www2.jpl.nasa.gov/srtm/).

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resolution (Davies and Guinotte, 2011; Yessonet al., in press). These indicate that suitable habitatfor these organisms exist on deep slopes andseamounts within the Chagos MPA (Davies andGuinotte, 2011; Yesson et al., in press). Giventhe lack of a history of deep-sea fishing in theregion around the Chagos Archipelago, it is likelythat associated communities of invertebrates and fishare still largely intact, unlike on most other ridges inthe Indian Ocean that have been fished or which aresubject to continuing or expanding fisheries.

Given the lack of research in general on equatorialseamounts, the MPA is thus particularly importantfor deep-water ecosystem conservation, both at aregional and global level. It also provides a uniqueopportunity to investigate the energetic links betweenproduction associated with shallow-water coralreefs and deep-water ecosystems, an area of marineecology that has not been explored.

PELAGIC FISHING AND FISHERIES

While no deep-sea trawling has been recorded in theChagos EEZ, there have been impacts from fisheriesoperating in both in-shore and pelagic environments.These fisheries providedmost income for Chagos untilthe cessation of fishing licences after the MPA wascreated, with the last licences expiring on 31 October2010. The main fisheries were a longline and purseseine fishery for tuna, and an inshore fishery. Thereis also a small recreational fishery in Diego Garcia.

The longline fishery in Chagos waters was activeyear-round, mainly under Taiwanese and Japaneseflagged vessels targeting large pelagic species,including yellowfin tuna (Thunnus albacares) andbigeye tuna (Thunnus obesus), swordfish (Xiphiasgladius), striped marlin (Tetrapturus audax) andIndo-Pacific sailfish (Istiophorus platypterus), withannual catches ranging from 371–1366 tonnesover the last 5 years (Koldewey et al., 2010). Thepurse-seine fishery targeted yellowfin and skipjacktuna (Katsuwonus pelamis) and was highly seasonal,operating between November and March with apeak usually in December and January (Meeset al., 2009). Log book records show that catches,mainly by Spanish and French flagged vessels, werehighly variable, ranging from less than 100 toaround 24 000 tonnes annually over the last 5 years(Koldewey et al., 2010).

The Mauritian inshore fishery targeted demersalspecies, principally snappers, emperors, and groupers,and logbook records indicated that catches werebetween 200 and 300 tonnes per year for the period

1991–1997, decreasing to between 100 and 150 tonnesfrom 2004 (Mees et al., 2008).

The recreational fishery on Diego Garcia is muchsmaller, taking (in 2008) 25.2 tonnes of tuna andtuna-like species (76% of the catch), the remainderbeing reef-associated species (Mees et al., 2009).

As with most fisheries, those in Chagos sufferedfrom poor documentation of by-catch and illegalfishing. By-catch was inadequately recorded througha log book system supported by limited observercoverage – mean observer coverage was 1.24% perseason for longline fishing and 5.56% for purse-seinefishing (Koldewey et al., 2010). Even with thisuncertainty, the by-catch in the Chagos was clearlysubstantial, particularly for sharks, rays, and billfish(Pearce, 1996; Anderson et al., 1998; Roberts, 2007;Graham et al., 2010; Koldewey et al., 2010). Thereis also evidence of marked harvesting effects onholothurian (sea cucumber) populations as a resultof poaching (Price et al., 2010).

Illegal fishing remains a management issuefollowing the implementation of the MPA andenforcement will be key to its effectiveness. Reefsharks in Chagos have declined by over 90% in a30 year period (1975 to 2006), attributed primarilyto poaching by illegal vessels (Anderson et al.,1998; Graham et al., 2010). The size and locationof Chagos as an MPA is particularly importantas the western Indian Ocean has some of the mostexploited, poorly understood, and badly protectedand managed coastal and pelagic fisheries in theworld (Kimani et al., 2009; van der Elst et al., 2005),while overall catches continue to dramatically increase(FAO, 2010). Chagos is within the remit of theIndian Ocean Tuna Commission (IOTC), althoughthis Regional Fisheries Management Organization(RFMO) is recognized to have numerous legal andtechnical weaknesses (Anon., 2009). Tuna in theIndian Ocean are considered to be close to themaximum sustainable yield (bigeye) or overexploited(yellowfin) and even skipjack, which is generallyconsidered a highly productive and resilient species,has been highlighted for close monitoring (IOTC,2010). Illegal, unreported and unregulated fishingis not a trivial component of the catch and addssubstantial uncertainty into assessments (Ahrens,2010).

There is increasing evidence that large MPAslike Chagos can benefit pelagic species that exhibithighly mobile behaviours (reviewed in Gameet al., 2009; Koldewey et al., 2010). In fisheriesmanagement, the phrase ‘highly migratory’ oftenhas little biological meaning, with studies of

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tuna mobility demonstrating they would benefitfrom national-level closures (Sibert and Hampton,2003). Pelagic fish demonstrate considerablestability and persistence, and predictability ofsome habitat features does occur within the pelagicrealm (Hyrenbach et al., 2000; Baum et al., 2003;Worm et al., 2003; Etnoyer et al., 2004; Alpine,2005). Migratory predators like tuna do not moverandomly, but associate with certain environmentaland/or physical features (Hughes et al., 2010;Schaefer and Fuller, 2010), meaning that positive,measurable reserve effects on pelagic populationsexist (Hyrenbach et al., 2002; Roberts and Sargant,2002; Baum et al., 2003; Worm et al., 2003, 2005;Jensen et al., 2010). Several studies have shown thatmigratory species can benefit from no-take marinereserves (Polunin and Roberts, 1993; Palumbi, 2004;Beare et al., 2010; Jensen et al., 2010).

Pelagic MPAs are an important tool in marineconservation management (Game et al., 2009) andare rapidly becoming a reality (Pala, 2009),although some of the challenges relating to theirimplementation may be both costly and difficult(Kaplan et al., 2010). Large MPAs are considerednecessary to protect migratory species such as largepelagic fish and marine mammals (Wood et al.,2008) as well as offsetting the concentration offishing effort outside them (Walters, 2000) andmaintaining ecological value (Nelson and Bradner,2010). Their importance for top predators has beenhighlighted by the most comprehensive, decade-long,open ocean tagging study in the Pacific that clearlydemonstrated that top predators – including whales,seals, tuna, sharks, seabirds and turtles – exploit theirenvironment in predictable ways, providing thefoundation for spatial management of large marineecosystems (Block et al., 2011). Extending to200 nm, the Chagos MPA offers an extremelyvaluable opportunity to understand the effects oflarge-scale protection on pelagic, migratory species,both within the MPA and within a regional context.Ranges of skipjack and yellowfin tuna have not beenmeasured in the Indian Ocean, but if their ranges in aPacific archipelago (Sibert and Hampton, 2003) aresuperimposed onto the Chagos MPA, it is seen thatthe latter encompasses as much as the median lifetimedisplacement of these two key species (Figure 10).

BIOLOGICAL CONNECTIONS OF CHAGOSIN THE INDIAN OCEAN

To the east of Chagos, there is no shallow wateruntil the Cocos-Keeling islands 2750 km to the

east, with Indonesia another 1000 km further on.To the west, distances to shallow reefs are muchless, 1700 km to the Seychelles and only 1050 kmto the commonly overlooked Saya de Malhasubmerged banks at the northern end of the‘Shoals of Capricorn’ between the Seychelles andthe Mascarenes (Figure 11). Ocean currents passingacross Chagos flow towards south-east Asia fromapproximately January to April, and towards thewestern Indian Ocean for much of the rest of the

Figure 10. The median lifetime displacement of skipjack (red) andyellowfin tuna (yellow), superimposed on a map of the Chagos MPA

(ranges from Pacific: Sibert and Hampton, 2003).

SocotraLakshadweep

Maldives

Chagos

GraniticSeychelles

Seychellesatolls

Saya de Malha

Nazareth Bank Cargados Carajos(St Brandon)

Mascarenes

Figure 11. Reef substrate or limestone banks within the photic zone inthe central and western Indian Ocean.

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year, with fluctuations (Couper, 1987). At a speed of0.5m s-1 (Bonjean and Lagerloef, 2002) planktoniclarvae from reef species would need 65days to reachshallow habitat in the east, but only 35 and 25daysto reach the Seychelles and Saya de Malha reefsystems, respectively, well within the pelagic larvalduration of many reef organisms. Due to itslocation, Chagos is thus likely to be an important‘stepping-stone’ for marine organisms in theIndian Ocean.

Fifteen years ago, mapping methods in whichgeographical distances were replaced by similaritiesof coral presences, showed that Chagos does appearto function as an east–west stepping stone for corals(Sheppard, 1999c). Another study has shown recentcolonization of a fish species from the east, consistentwith this stepping-stone function, especially with reefsin the southern part of the group (Craig, 2008).

Genetic programmes to examine connectionsbetween Chagos and other Indian Ocean reef siteshave been initiated recently for numerous species,including about 24 reef fish species and severalinvertebrates. For hawksbill turtles (Eretmochelysimbricata), genetic linkages were demonstrated fornesting females and foraging juveniles betweenChagos and Seychelles, but no linkages weredemonstrated with hawksbill rookeries of WesternAustralia (Mortimer and Broderick, 1999; Mortimeret al., 2002). In the wider Indian Ocean, Vargas et al.(in press) subsequently identified nine geneticgroupings, with those nesting in Chagos andSeychelles forming a single grouping distinct fromthose in the Arabian Gulf and from easterly sitesincluding Western Australia (Vargas et al., in press).Analyses of DNA indicate that most foraginghawksbills in Chagos derive from rookeries inChagos and Seychelles, which also contributesubstantially to foraging aggregations in CocosKeeling (FitzSimmons, 2010, unpublished report).Although most mtDNA haplotypes found in theChagos and Seychelles were not found elsewhere,some uncommon haplotypes were identical to thoseobserved from Iran, Oman, and Australia, supportingthe stepping stone model.

The crown-of-thorns starfish, an important coralpredator, was previously believed to be a singlespecies, Acanthaster planci, but Vogler et al. (2008)have shown that the species includes four highlydifferentiated lineages with restricted distributions,which together form a species complex. Two ofthese lineages are found in the Indian Ocean, anddata indicate (Figure 12(a)) that crown-of-thornsstarfish from Chagos belong to the Southern Indian

Ocean lineage. A more detailed phylogeographicstudy (Vogler et al., in prep.) reveals that there ishigh gene flow among populations of the SouthernIndian Ocean lineage, indicating high connectivityamong these geographically distant populations.In other parts of the Pacific, larvae have been foundto extend their developmental period to seven weeks

Figure 12. (a) Crown of thorns genetic groupings. (b) peacock hind(Cephalopholis argus). (c) brown surgeonfish (Acanthurus nigrofuscus).(d) coconut crab (Birgus latro). Colour coding for the crown of thorns(Vogler et al., 2008, in prep.) and peacock hind (Gaither et al., 2011)indicate distinct genetic lineages. Dashed lines for the brownsurgeonfish (Eble et al., 2011) indicate genetically independent populations.Photo credit: www.aquaportail.com. Image 12(b) and 12(c) reprinted fromGaither et al. (2011) and Eble et al. (2011) with permission from theauthors. For (d) solidity of arrow lines represents relative amounts of geneflow, so that for this terrestrial crab flow is mainly eastwards during the

Equatorial Counter Current flow.

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in marginal food regimes (Lucas, 1982). Althoughthe occurrence of a facultative teleplanic larvaremains to be confirmed (Birkeland and Lucas,1990), the low productivity found over most ofthe southern Indian Ocean (<130 gC m-2 day-1;Reid et al., 2006) could result in extended larvaldurations there too, and hence the observed highconnectivity. This would contribute to the lowlevels of genetic structure observed in the SouthernIndian Ocean lineage, despite the geographicdistances among populations.

Genetic surveys of reef fish species (Eble et al.,2011; Gaither et al., 2011) show an affinity withthe western Indian Ocean. The peacock hind(Cephalopholis argus, Figure 12(b)) and brownsurgeonfish (Acanthurus nigrofuscus) (Figure 12(c))demonstrate genetic similarity within sites in thewestern Indian Ocean and much less similarity withsites further east.

Preliminary examination of the coral Platygyradaedalea with five microsatellite loci, includingsamples from Chagos (Macdonald et al., personalcommunication), revealed the intuitive result that,while the Chagos population had the lowest allelicdiversity among the sites studied, it proved to be asource of genetic diversity for this species. The roleof Chagos as a stepping stone between the east andthe west of the Indian Ocean, or a recipient of larvae,is further suggested by coral species diversity patterns(Obura, unpublished; Figure S6 in SupplementaryMaterial). Based on consistent field samples from2002–2010, the coral fauna of Chagos is more similarto that of the western Indian Ocean continentalcoastline, including northern Madagascar, than it isto the smaller andmore dispersed islands in the centralIndian Ocean (Seychelles, Mauritius, Reunion). Interms of species richness it groups with the continentalsites, potentially due to both connectivity and habitatarea (Figure S6 in Supplementary Material).

Despite being geographically part of the IndianOcean, the eastern Indian Ocean locations atCocos- Keeling and Christmas Islands, and WesternAustralia are more closely affiliated with thePacific ichthyofauna, with only 5% of speciesat Cocos-Keeling being exclusively of IndianOcean origin (Allen and Smith-Vaniz, 1994). Thelatter islands are considered to be a part of theIndo-Polynesian Province stretching from the easternIndian Ocean to Easter Island (Briggs and Bowen,2012) and have been shown to be sites of hybridizationbetween Indian and Pacific Ocean populations ofreef fishes (Hobbs et al., 2009). Exceptions tothis pattern include a dispersive snapper (Lutjanus

kasmira; Gaither et al., 2010), trumpetfish (Bowenet al., 2001) and twomoray eels (GenusGymnothorax,Reece et al., 2010) which freely intermix across alltheir Indo-Pacific range and Chagos may act as abridge between western Indian Ocean and Pacificpopulations of these species.

For the coconut crab, Birgus latro, which isterrestrial but which breeds in the sea, mitochondrialgenetic work has compared Chagos with sites in theSeychelles and East Africa, and showed that theChagos population was significantly differentiated(P <0.05) from Seychelles and East Africanpopulations (Table S1 in Supplementary Material).Asymmetric gene flow, favouring migration fromEast Africa to Seychelles, and Seychelles to Chagos,comes from estimates on direction and mean numberof migrants per generation between regions. The rateof immigration toChagos from thewest wasmeasuredat about five effective females per generation (breedingage commences after about 5 years), using a measuredmean effective female population size in the study ofabout 3000, or about 0.1–0.2% per generation(NB this is not the counted population of individuals,which is orders of magnitude greater). Thus for thisspecies, Chagos receives more larvae from the westthan flow from Chagos to the west (Figure 12(d);Tables S1–S3 in Supplementary Material) partlybecause egg release coincides with the period ofcurrent flow towards the east, and there is a high levelof genetic connectivity. Additionally, a strong geneticconnectivity among three sites was also seen throughpopulation structure analysis. The data also show thatthere is a clear differentiation between the IndianOcean clade and the west Pacific clade (Figure S7 inSupplementary Material).

Taken together, these results confirm that Chagosis part of the western Indian Ocean province asdescribed by Briggs (1974), although Briggs andBowen (2012) comment that it has faunal affinitieswith the Indo-Polynesian province, with respect tofishes, as well as to the western Indian Ocean.Interestingly, Chagos shows less connectivity in somegroups than might be expected (considering the muchshorter distances) with the much closer Maldivesto the north, which may be a function of thepredominantly east–west currents. The pattern isclearly complex: earlier fish surveys (Winterbottomand Anderson, 1997) in the Chagos Islands delineatedthe archipelago into two distinct assemblages, withthe northern portion sharing affinities with the easternIndian Ocean and the southern portion (includingDiego Garcia) more closely aligned with faunalassemblages further west.

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Thus the results from the genetic and distributiondata indicate that Chagos is an importantbiogeographic crossroad between the eastern andwestern Indian Ocean. The so-far limited moleculardata show that the distances between Chagos andthe western banks and Seychelles is much less of abarrier than is the much larger expanse of waterto the east. Development of so-called ‘teleplaniclarvae’ by which many species show greatly expandedlarval durations, especially in conditions of lownutrients (such as exist in the central Indian Ocean)and lack of suitable substrate, has been longrecognized (Scheltema, 1988). Some coral larvaemay be competent for up to 105 days (Wilson andHarrison, 1998), and while the pelagic larvalduration of reef fishes averages about one month, itvaries enormously (Brothers and Thresher, 1985;Sale, 2002). Although it is probable that Chagos isan important stepping stone in the western IndianOcean, the rate at which this happens for most groupsis still not known (though values show appreciablemixing of the island-requiring coconut crab as notedabove). In fact, the number of migrants needed tomaintain genetic coherence between populations issmall (Slatkin, 1977, 1982). As noted by Hellberg(2007), for management purposes we need toknow whether or not connections are made everyseveral thousand generations, or if only a singlefounding event occurred, or whether connectionsoccur in ecologically frequent intervals. Patternsof connectivity as they exist today are especiallyimportant for designing management strategies torestore and conserve reef populations. If Chagos ismainly a net recipient of larvae then its rich andrelatively undamaged state affords it a very highconservation value. If Chagos is also a source ofbiological diversity for the over-exploited sitesfurther west, then its value would be even greater.

ISLANDS OF THE MPA

Because of its relatively large land size (29.7 km2)Diego Garcia has been the site of most terrestrialresearch (Stoddart and Taylor, 1971). During itsplantation period, Diego Garcia, along with mostother islands of Chagos, was heavily plantedfor coconut at the expense of the native plantcommunities. Stoddart (1971) expressed surpriseat the large proportion of land area used forcoconut production: ‘. . .almost the whole area ofthe atoll (6250 out of 7488 acres) was beingcropped for coconuts’ and

“Little attention has been paid at Diego Garciato conservation: the atoll has simply been used asa supplier of coconut products, and to a lesserextent of dried fish and turtles, for Mauritius.Both the Green and Hawksbill turtle used to nesthere in some numbers. . . The early settlers foundthe frigate birds, boobies, noddies, terns, heronsand tropicbirds to ‘breed on these islands. Theyare considered good eating; the feathers too,make excellent bedding’ (Anon. 1845, 483).”

The island was severely damaged in ecologicalterms. Guano mining and habitat destructionaccompanying the plantations destroyed most birdsand nesting habitats, including some huge terncolonies, along with other species now listed in theIUCN Red List such as turtles and coconut crabs(IUCN, 2011). Stoddart reports that the first practicalconservation measures were taken by a manager inthe 1870s, but ‘in the absence of enforcing authorityor of any clear need for conservation it is unlikely thatmuch attention was paid to it.’ The same lack ofconservation ethic applied to other Chagos atollstoo, as with coral islands throughout the ocean.

The military facility was constructed mainly inthe early 1970s. It was built on former coconutplantation – little or no intact natural vegetationor bird colonies remained. Partly because ofconservation requirements developed over the last20 years, Diego Garcia has several conservationsites and issues of its own (Figure 13). It is one ofthe most enclosed atolls in the world, being openin the north only, with three small islets in themouth. The military facility is located on the westernarm. The eastern arm is part of a Ramsar site(JNCC: Ramsar Site UK61002), which extends3 nm to seaward, encompassing most of the lagoonalso. There are four Strict Nature Reserves: on theeastern arm south to line ‘A’ in Figure 13, andaround the three islets, into which access isprohibited. Access to the part of this arm southof line ‘A’ is permitted. ‘Turtle Cove’ has specialconservation status and restrictions because of itslarge aggregations of foraging juvenile and subadulthawksbill turtles, which have been the subject ofmark–recapture, genetic analysis, blood hormoneanalysis, and population research (Mortimer andBroderick, 1999; Mortimer and Crain, 1999;Mortimer and Day, 1999; Mortimer et al., 2002).

Underwater, the northern and deepest third ofthe lagoon was subjected to significant blastingand removal of surface-reaching coral growths, to

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create the present large anchorage. This causedmuch damage in that area at that time, though abrief survey of eight locations in 1979 (Sheppard,1980b) showed that by that time coral cover hadrecovered in areas where there was no anchoring,being similar to values in the northern atolls whereno activities of any kind had occurred for severalyears. During the 1970s, there was no indicationthat coral growth was other than vigorous inmost of the world, though the extent of the lagoonrecovery was more rapid than expected. To theauthors’ knowledge, no further dredging or blastingactivities have taken place after that initial period.

Pollution monitoring

Extensive pollution monitoring takes place in DiegoGarcia. ‘Final Governing Standards’ and routineprocedures require regular analyses inUS laboratoriesof over 100 metals and organic substances accordingto US operating procedures. Almost all analysesreport levels below detectable or reporting limits.None have been found to be of concern, including oiland oil residues (data held by BIOT Administration).

In addition to the US monitoring, several specificprojects have set out tomeasure emerging compoundsof particular interest or concern (see SupplementaryInformation text for more detail about all substancessummarized below).

Hydrocarbons have been particularly focusedupon, and most have a natural origin (Readmanet al., 1999). There was negligible evidence ofcontamination from petroleum. Polycyclic aromatichydrocarbons (PAH) were similarly very low, andReadman et al. (1999) also found no evidenceof sewage contamination. PCBs and organicpesticides were mostly below instrument detectionlevels. Similarly, extremely low levels occurred forpolyfluorinated compounds, brominated, chlorinatedand organo-phosphorus flame retardants, fluorinatedtensides, and surfactants (PFOS) (Wolschke et al.,2011). Antifouling booster biocides and triazineherbicides (Guitart et al., 2007) also were negligible,with levels generally below the limit of detection.The same pattern occurred with most metals, thoughof interest is that some elevated copper was detectedin 1996 in some northern waters, attributed tocopper in fungicides used in coconut agricultureseveral years earlier (Everaarts et al., 1999).Comparisons with Antarctic and remote deep seasamples for many showed this area to have theleast chemical contamination so far recorded(Supplementary Information).

There has been no oil or tar seen on DiegoGarcia beaches to date, although a little has beenseen on some northern islands. Lagoon water nearships is likewise monitored and is also devoid ofthese substances. In summary, from a chemicalcontaminant perspective, the marine environmentsurrounding the Chagos Archipelago can beconsidered to be near pristine and in chemicalpollution terms, Diego Garcia is likely to be thecleanest inhabited atoll in the world.

Shoreline debris

Despite their near pristine chemical status, Chagosbeaches have a surprisingly high number of piecesof debris. Observations were made in 1996, 2006,and 2010 at 20 sites in the outer atolls, and one inDiego Garcia (Price, 1999; Price and Harris,2009). Median scores of the number of litter pieceswere high in all years; >1000 items per 500m linearbeach. Items were mainly plastics, polystyrene(Styrofoam) and rope, much being lost fishing gearor debris discarded from ships, most commonly ofsouth-east Asian origin. Levels in Diego Garcia in

Figure 13. Map of Diego Garcia atoll. The military facility is on thewestern arm. Gray line shows the Ramsar site, which encompasses mostof the lagoon, extending seaward on the eastern side. The eastern armsouth approximately to the line where the Ramsar boundary intersectsthe coast is a ‘Nature Reserve’ which covers land only. From the top ofthe eastern arm to the line marked ‘A’, plus the three circled islets in themouth of the atoll, are ‘Strict Nature Reserves’, which each cover land

plus the sea area extending out 200m from shore.

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all years were two orders of magnitude less than inother atolls, reflecting periodic clean-up events inthat inhabited atoll. The method did not determinesize categories or weight; most items were a few cmin size or less, but several northern islands appear tocollect substantial volumes of larger flotsam.Similar numbers are found in remote Pacific atolls(Price and Harris, 2009) where ocean current gyresare the main transport vector. Driftwood and losttimber from ships was low on beaches in all years,but decreased over time from 1996 to 2006, attributedto use for fuel by illegal fishing camps on the islandsduring this period of increasing fishing pressure (Priceand Harris, 2009; Price et al., 2010). Oil slicks werenever seen, but tar balls were seen at eight beachesin 1996, at three in 2006 and at one in 2010, nonebeing seen in Diego Garcia. The decrease mayreflect improved international ship ballast cleaningmeasures over that period (Price, unpublished data).

Terrestrial flora

Being geologically young, remote, isolated, flat, andnever connected to a continental land mass, theChagos islands have a naturally impoverishednative flora. There are probably 45 native speciesof higher plants, 41 flowering plants (12 trees) andfour ferns, none of which are endemic (Topp andSheppard, 1999), most having a widespreaddistribution across the region. There are severalimportant native vegetation community types withexamples remaining intact, especially on islands toosmall to have been used in plantation times. Theseinclude Pisonia forest and Lumnitzera mangroveson Moresby Island; Scaevola-Argusia beachcommunities on many islands and Calophyllumthickets on Ile Takamaka. Most plants, especiallyon Diego Garcia, were introduced for fruit orornament, or accidentally as unwelcome passengersof incoming cargo (Topp and Sheppard, 1999). Somespecies are problematic. The native dodder (Cassythafiliformis), a parasitic vine, is spreading rapidly andover-topping some of the native vegetation. Pipturusargenteus, a shrub whose origin is in doubt, isspreading widely and is having some negativeimpacts on regenerating native trees such as Pisoniagrandis (Clubbe, 2010).

Introduced plant species are far more numerousthan the native species. An updated vascular plantchecklist (Clubbe, unpublished data; Hamiltonand Topp, 2009) shows that 232 non-native specieshave been recorded, with 128 listed as only occurringon Diego Garcia (Hamilton and Topp, 2009). Of

these, few show signs of invasiveness and most areunlikely to pose significant problems. However, thereare some species where control measures are needed.Most significant is coconut (Cocos nucifera), whichwas widely cultivated previously. Young palms forma dense understorey which exclude virtually all otherplants. Control measures underway in a pilot schemeon Diego Garcia involve the removal of palms toenable regeneration of native species from eithera recently established seed bank or from thosefew plants that are able to survive in the low-lightenvironment created by the coconuts. Regenerationis supplemented by enrichment planting of keynative tree species including Barringtonia asiatica,Cordia subcordata,Guettarda scabra andCalophylluminophyllum, all of which provide important nestingsites for seabirds. In Diego Garcia, there is a ‘twofor one’ policy whereby any coconut or other treeremoval is replaced by two hardwood trees collectedfrom seedlings beneath established trees or from theseed bank. If successful, this approach will be appliedto northern islands also. Some species of introducedplants are spreading invasively, some associatedspecifically with former settlement, e.g. Tabebuiaheterophylla, while others not specifically associatedwith settlement areas, e.g. Casuarina equisetifolia,exist on several islands. The latter, introduced fortimber in plantation times, poses a threat to nativetrees on some of the islands since it exerts a tenacioushold, out-competing other trees owing to the abilityof its roots to fix nitrogen and because of the litter itcreates.

More work is needed to fully understand thedistribution of non-native species and the potentialimpact of invasive plants in Chagos. Preliminaryanalyses indicate, however, that the spread ofnon-native species from Diego Garcia to otheratolls is slow and there has not been a noticeableincrease in the number of non-native species onthe outer islands since the 1980s (Clubbe, 2010).

Regarding algae, mosses, liverworts, cyanobacteria,fungi, and lichens, diversity is relatively low inChagos, although these provide high cover andare ecologically important (Seaward, 1999; Seawardand Aptroot, 2000; Watling and Seaward, 2004;Seaward et al., 2006). Cyanobacteria extensivelyclothe limestone, thin sandy soils and tree trunks,and fix nitrogen directly in the otherwise poorsoils. The mosses and liverworts are important instabilizing soils, and are often the primary stagesin the succession of higher vegetation in exposedareas. In wooded areas, the mosses and liverwortsclothe the bark of living trees; the nature of

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this epiphytic flora changes with age; as the trunksdie, different mosses and liverworts support thedecomposition process undertaken mainly by fungi.Lichens colonize all available tree bark surfaces, aswell as being found on the living leaves of various treespecies, the long-lived evergreen nature of the leavesallowing these slow growing organisms to establishthemselves.

There are no endemic species of these groups.However, due to the geographical setting of theislands their establishment is remarkable, not onlyin terms of the distances travelled by the sporesand propagules, but also in terms of their origin,and there are interesting affinities of these floraswith south-east Asia, India or Africa, as yet to befully determined. A new liverwort, Cololejeuneaplanissima var. chagosensis, known only from Chagos(Seaward et al., 2006), is likely to occur elsewhere, butthere is always the possibility that it has disappeared(or will disappear) from its original site(s).

Terrestrial fauna

There are no native mammals, amphibians orendemic birds. Of invertebrates recorded to date,most are widespread species with distributionsacross the Indo-Australian tropics and include somehuman commensals (Barnett and Emms, 1999).There are thought to be three endemic sub-speciesand one endemic species of Lepidoptera (Barnettand Emms, 1999).

The black rat (Rattus rattus) is the main invasiveanimal, and was reported to be of plague proportionsas early as the late 1700s. Only smaller islands whichwere not planted have no rats and have numerousbirds, and even islands close to rat-infested islandsremain uninvaded.

Other species introduced at various times in theislands’ history include sheep Ovis aries, cattle Bossp., horses Equus ferus, donkeys Equus africanusasinus and (having the worst impact on the birds),dogs Canus lupus., pigs Sus sp., cats Felis catus, aswell as the rats (Edis, 2004; Carr, 2011a). Most havegone, but remaining invasive animals include thecane toad (Bufo marinus), feral cats, donkeys andseveral birds (Carr, 2011b). Dates of introductionfor most terrestrial invasives are unknown, oneexception being the garden lizard (Calotes versicolor)in Diego Garcia. This was first observed on DiegoGarcia in May, 2001, and is believed to have beenintroduced via cargo. It is arboreal, diurnal andadaptable (Daniel, 2002) and is one of the mostwidespread non-geckonid lizards in the world

(Matyot, 2004). It has a population density of 172lizards ha-1 (95% CI: 154–237) in the inhabited area,has since spread south and is likely to spread islandwide. This illustrates the rapidity at which suchspecies may spread. Since that time, strict quarantinemeasures have been introduced for importedmaterials, including rock for construction ofhardened shorelines to combat shoreline erosion.

Seabirds

In contrast to the generally poor terrestrialfauna, the breeding seabirds of the Chagos are ofinternational importance (Carr, 2006, 2011a).Islands never planted, inhabited or rat infestedgive a glimpse of what the islands used to look likebecause significantly higher bird abundances occuron these (Symens, 1999; Price and Harris, 2009).

Population trends and the seabirds’ breedingphenology are poorly understood. Comprehensivecensuses were undertaken of breeding seabirds inFebruary/March 1996 (Symens, 1999) and againin March 2006 (McGowan et al., 2008; Figure S8in Supplementary Material). Eighteen seabirdspecies breed in Chagos (Carr, 2011a), five inglobally important numbers, resulting in ten islandsbeing classified as Important Bird Areas (IBAs)(Carr, 2004, 2006, 2011b), with two further islandsbeing proposed as IBAs (McGowan et al., 2008).Recently more regular monitoring of the ChagosIBAs showed that many species of seabird eitherbreed continuously throughout the year with spikesin breeding in certain months, e.g. red-footed (Sulasula) and brown (Sula leucogaster) boobies, or breedat different times of the year on different atolls, e.g.lesser noddy (Anous tenuirostris) and sooty tern(Sterna fuscata) (Figure S8 in SupplementaryMaterial). This realization of continuous breedinghas increased the estimates of some of the breedingpopulations of some species, making the Chagosseabirds an even more important asset than waspreviously believed, to both the Indian Ocean andglobally. Diego Garcia and its three associated isletshold one of the Indian Ocean’s largest breedingcolonies of red-footed booby, which has grown fromthree or four pairs in 1984 to over 5000 pairs in2011, spread over 30km of shoreline (Carr, 2011b).This growth may be attributable to the area beingout of bounds to all personnel since 1984.

The suggestion has been made that the ten IBAsshould be clustered into four grouped IBAs, whichwould ‘. . . be consistent with IBA philosophy indesignating inter-connected, proximal, protected

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habitats for species that . . . appear to utilise differentislands for breeding in different seasons’ (Carr,2011b). These four would consist of Diego Garcia,the Western Great Chagos Bank Islands, Nelson’sIsland in the northern Great Chagos Bank, andthe eastern islands of Peros Banhos atoll. Toinitiate successful conservation management plansfor seabirds, a thorough understanding of theirbreeding phenology is essential, including breedingtriggers and dietary requirements. Long-term,scheduled monitoring is required to achieve this,in order to preserve and protect one of the lastseabird strongholds in the Indian Ocean.

Coconut crabs

The coconut or robber crab (Birgus latro) has awide distribution throughout the Indian and PacificOceans but is usually over-harvested. The largestland dwelling invertebrate in the world, it canexceed 5 kg. They mate on land but the femalereleases eggs in the ocean after a few months, wherethey immediately hatch, the oceanic larval stageusually lasting 2–3weeks (Fletcher and Amos,1994). Once on land their growth is slow; theymay be mature at 5 years but it takes approximately8–10 years (depending on diet quality) for crabs toreach a size of ~500 g, with maximum size at40 years (Fletcher and Amos, 1994).

Many of the northern islands in the 1970s hadvery few coconut crabs, and they were virtuallyabsent from some. Those seen had a size positivelycorrelated with the length of time that the islandhad been uninhabited, ranging from the 1930s whenthe first two of the five atolls were abandoned, to the1970s (Sheppard, 1979). In 2010 in Diego Garcia,crab populations showed an overall average densityin the Ramsar area of 298 crabs ha-1 (95% CI:229–387, Figure S9(a) in Supplementary Material),the highest average number ever recorded, with twotransects containing 467 and 489 crabs ha-1 (Vogt,unpublished). The southern tip of the island had anaverage 147 crabs ha-1 (95% CI: 95–226), while theside containing human habitation had only 39 crabsha-1 (95% CI: 24–63) indicating capture despiteregulations, and the inhabited side also lackedcrabs in the largest size classes (Figure S9(b)in Supplementary Material). The Ramsar sideappears to be unharvested, a rarity for this species.

Turtles

Hawksbill (Eretmochelys imbricata) and green turtles(Chelonia mydas) nest in Chagos, and surveys

conducted in 1996 and 2006 recorded both speciesat each of the five atolls. Estimated numbers offemales nesting annually were 400–800 green turtlesand 300–700 hawksbills in 1996 (Mortimer andDay, 1999). Diego Garcia, by far the largest islandin the group, has nesting populations of both speciesthat rival those of any of the other atolls, and nestingdensity and habitat quality are particularly goodalong the east coast.

Historical records indicate that nesting numbersof both species declined significantly over the periodof human settlement (Mortimer and Day, 1999;Mortimer, 2009). In 1786, more nesting greenturtles were captured at Salomon atoll in 4 daysthan were estimated to nest there annually in 1996(Mortimer and Day, 1999). Likewise for hawksbills:trade statistics show that at the turn of the 20thcentury nearly as many were killed annually toprovide shell for export, as were estimated to nesteach year in 1996 (Mortimer, 2009; Figure S10 inSupplementary Material). A comparison of nestingcensus data from 1996 and 2006 (Mortimer, 2007)indicates little change in hawksbill nesting activityin the northern atolls, but a possible increase atDiego Garcia. Levels of green turtle nesting recordedat all island groups were greater in 2006 than in1996. However, this does not necessarily indicatepopulation increase, given that green turtle nestingactivity oscillates from year to year and trends canonly be discerned when nesting activity is monitoredconsistently over extended periods of time (usuallymore than 10 years).

Island prospects, erosion and sea levels

Though tiny in total area compared with marinehabitats, the islands are central to conservationmeasures. Much has been discussed recently aboutloss of coral islands from climate change; indeedthe nearest archipelago, the Maldives, has taken alead among small nations in this matter. Controversyabout island erosion and sea level rise has beenstrenuous because the subject has many apparentcontradictions.

Sea-level rise in the southernmost atoll DiegoGarcia has been recorded by tide gauges since 1988(Figure S11 in Supplementary Material). The dataare in two series, (1988–2000 and 2003 to present),the former being ‘research grade’, the latter being‘fast delivery’ data only at present. Both series havegaps and, while the graph shows a substantial rise,both series are short. The two nearest tide gauges toChagos are on Gan in the southern Maldives, 475km

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north at about 1oS and on the capital Malé at about4oN (Singh et al., 2001). These show rises of similarorder to that in Diego Garcia. Further, there aremarked seasonal differences in monthly averages, bothinDiegoGarcia and in theMaldives, which Singh et al.(2001) link to the monsoon cycle. Highest monthlyaverage tides in Diego Garcia occur in November–February, and the lowest ones between April and July.

Newer satellite altimetry data shows a muchsmaller rise compared with tide gauge measurementsfor the central Indian Ocean (www.sealevel.colorado.edu), including both Chagos and the Maldives. Localland movements may account for an unknownproportion of the discrepancy between gauges andsatellite altimetry, but whether gauges or satellitealtimetry are more correct, it is high tides, notmonthly averages, which cause flooding, andseveral other oceanographic and climate drivenchanges may be more important. Further, differentatolls may respond slightly differently toDiegoGarciain terms of relative sea level rise because the area istectonic, lying on a minor plate margin (Figure S12in Supplementary Material). Local effects are alsodependent on supply of sediments, which is likely tohave changed markedly following the massive coralmortality of 1998.

The important immediate consideration iserosion of shores and inundation by the sea, ratherthan sea-level rise per se. Coral islands have longbeen known to have mobile shores because ofnatural annual or decadal shifts in sedimentationdriven by climate, which affects wave height, swell,and swell direction (Young et al., 2011in press) aswell as sea level. Chagos has suffered considerableoverall erosion of many shorelines, most notablyin the last decade. This has not yet been studied indetail, although in Diego Garcia it is most noticeableif only because of the high cost of sea defencemeasures employed there. In parts of the northernatolls, horizontal attrition may exceed 1myr-1 inseveral areas although this high rate is episodicand spatially patchy. On several islands, remnantsof mature coconut trees are now in the intertidalzone, and pits dug for coconut cultivation are nowat or below high tide levels in some places, allindicating net erosion over the past 100–150 yearsin such places. Blenheim atoll in the north used tohave three low sandy islands, with low bushes(report by Archibald Blair, 1787) but this atoll isnow submerged, with only some sections of itswestern rim emergent at low tide. This atoll’s coraland algal ridge growth are as prolific as on nearbyislanded atolls, so a deficiency in reef growth is an

unlikely cause of the drowning. In contrast, Egmontatoll, was known in the 19th century as the ‘SixIslands’ (each named separately), yet today mosthave fused to form only three islands at low tide,possibly because of tectonic movement or becauseof changing sedimentary patterns, although erosionas described above also occurs in some sectors.Coral mortality from warming, discussed earlier, islikely to lead to massive if temporary changes insand production, known to have had markedconsequences on shorelines elsewhere in the IndianOcean for example (Sheppard et al., 2005).

Island heights and cross-sections are likely to beimportant to future events. The highest points ofprobably all islands occur on the rims. Profiles ofseveral Chagos islands (Figure 14) show a centraldepression, caused by acidic rain eroding the

Figure 14. Cross-sections of (a) Sipaille, (b) Lubine, (c) Sudest islands inEgmont atoll, (d) Isle de Coin on Peros Banhos atoll, and (e) IleBoddam on Salomon atoll. Y-axis is metres above mean high tide in(a)–(c), and from a relative datum in (d)–(e). (a) Lagoon is on right,total width is 500m, (b) lagoon on right, total width 450m, (c) lagoonis on left, total width 250m. (d) and (e) have no horizontal dimensionsbut are larger islands. Solid horizontal lines are mean high watersprings. (a)–(c) from Sheppard (2002), (d)–(e) from Royal Haskoning(2002). Dashed lines in (d)–(e) are estimated flooding levels following

severe storm overtopping.

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coral limestone rock (Sheppard, 2002), and byaccumulation of sand around island rims. Futureerosion patterns are unlikely to be smoothlyprogressive, and may be episodic. There is evidenceof this in several locations, and a broach coulddestroy the freshwater lens in that area. Figures 14(d)–(e) also shows potential inundation levels intwo islands in two northern atolls, determinedby Royal Haskoning (2002) in a resettlementfeasibility study. In Diego Garcia atoll also,similar central depressions are evident on bothwestern and eastern sides, although much of theeastern arm is very narrow and low lying too, suchthat extensive flooding occurs at high spring tides.

A further phenomenon, noted over 100 years agobut which has been largely overlooked, is that of‘self-gravitation’, whereby the large volume of iceadded to the poles creates significant gravitationalattraction of its own (Vermeersen, pers. comm.;Vermeersen and Schotman, 2009), raising waterlevel nearer the poles. Thus, when ice melts andwater redistributes, polar gravitational attractionlessens, so sea-level rise increases the further thedistance from the ice sheet (along with a markedfall near the poles). The magnitudes are likely tobe significant to tropical coral islands because, inthe absence of the Greenland ice sheet’s gravitationalattraction, sea-level rise in equatorial regions wouldprobably be 10–20% greater than would occur fromice volume melt alone (Vermeersen, pers. comm.).

CLIMATE AND LONG TERMENVIRONMENTAL MONITORING

PROGRAMMES

Work is increasingly needed on climate changeprojections, yet the Indian Ocean forms a very largegap in many global monitoring programmes. Chagosis situated in a key region of climate variability. It liesat the eastern margin of an oceanic feature known asthe ‘Seychelles–Chagos thermocline ridge’ (Hermesand Reason, 2008), along which the thermocline risesclose to the surface and upwelling of cold water frombelow the thermocline occurs (Vialard et al., 2009).In contrast to most upwelling regions, surface waterof the Seychelles–Chagos ridge is extremely warm.In austral summer, the main rainy season, sea surfacetemperature (SST) varies between 28.5 �C and 30 �Conly, a range in which the atmosphere is very sensitiveto small oceanic changes (Timm et al., 2005). The highSST combined with the shallow thermocline makesthe Seychelles–Chagos ridge a region with very strongair–sea interactions.

However, climate observations from this region areextremely sparse due to the paucity of measurementsin most Indian Ocean countries and to the remotenessof Chagos. Further, instrumental SST data areassociated with errors that are as large as theSST anomalies across a range of time scales(Annamalai et al., 1999). There is currently only oneweather station at Diego Garcia, whose weatherrecords contain several gaps (Sheppard, 1999d).‘Conventional’ infrared satellite measurements ofSST are not adequate to capture important SSTperturbations that occur in the rainy season whenconvective activity and cloud cover is highest(Vialard et al., 2009), and only the increased useof orbiting microwave instruments in the late1990s allowed better quality SST to reveal the roleof Chagos with respect to air–sea interactions(Vialard et al., 2009). Therefore, a continuousmonitoring programme of important climatic andoceanographic parameters at Chagos is neededfor a better understanding of air–sea interactionsthat are crucial in global climate issues.

The Seychelles–Chagos region has a distinctoceanic and atmospheric variability at multiple timescales, each with significant climatic consequences.It has the strongest intraseasonal SST variance inthe Indo-Pacific warm pool, because the shallowthermocline is very responsive to atmosphericfluxes (Vialard et al., 2008, 2009). SST cooling of1–1.5 �C, lasting for 1 to 2months, may occurduring austral summer, followed by a short lagand sharp increase in atmospheric convectiveactivity (Vialard et al., 2009) associated withthe Madden–Julian–Oscillation (MJO, Maddenand Julian, 1994). The MJO has a time scale of30–80days, and it explains much of the variance oftropical convection, and modulates cyclonic activity.

On interannual time scales, the Seychelles–Chagosridge is affected by the El Nino-Southern Oscillation(ENSO) and the Indian Ocean Dipole (IOD)(Saji et al., 1999; Webster et al., 1999). ENSOevents lead to a displacement of the West Pacificwarm pool and affect the Indian Ocean via theso-called atmospheric bridge. Anomalous subsidenceover Indonesia during El Nino years leads to acooling over the maritime continent and abasin-scale warming of the Indian Ocean, particularlythe western part. The IOD is a coupledocean–atmosphere instability centred in the tropicalIndian Ocean that affects the climate of the countriesthat surround the Indian Ocean basin (Marchantet al., 2007). A positive IOD period is characterizedby cooler than normal water and below average

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rainfall in the eastern Indian Ocean, Indonesia andover parts of Australia, while warmer water andincreased rainfall is observed in the western IndianOcean and equatorial East Africa. A negative IODperiod is characterized by warmer than normal waterand above average rainfall in the eastern IndianOcean sector and cooler than normal water andbelow average rainfall in the western Indian Ocean.Some studies suggest that positive (negative) IODevents may be triggered by El Niño (La Niña), whileothers find that IOD events occur independentlyalthough they may overlap with El Niño/La Niñaevents, e.g. the strong 1998 ENSO (Saji andYamagata, 2003). The IOD has two ‘centres ofaction’: one off the coast of Sumatra, in the easternIndian Ocean sector, and one at the ChagosArchipelago (Saji and Yamagata, 2003). Reliableinstrumental records of the IOD are currentlylimited to the past 50 years.

On decadal and longer time scales, informationon climate variability at Chagos has been gainedfrom geochemical proxies archived in long-livedcorals (Pfeiffer et al., 2004, 2006, 2009; Timmet al., 2005). These data suggest that changes inthe mean climate may influence the impact oflarge-scale climate phenomena at Chagos, possiblyaffecting climate in other countries surroundingthe Indian Ocean. For example, a shift towardshigher mean SSTs occurred in 1975 (Timm et al.,2005; Pfeiffer et al., 2006, 2009), after which smallSST changes induced by ENSO caused much largerprecipitation anomalies (Timm et al., 2005; Pfeifferet al., 2006). Similar changes in rainfall variabilityhave been found in South Africa (Richard et al.,2000), Sri Lanka and southern India (Zubair andRopelewski, 2006).

The long-term variability of the IOD has also beeninvestigated with coral proxies from the Seychellesand Indonesia (Abram et al., 2008). The coralreconstruction suggests an increase in the strengthand frequency of IOD events during the 20thcentury, which may also influence the distributionof rainfall in the tropical Indian Ocean. The workhighlights the importance of the Chagos Archipelagofor climate variability research in the Indian Oceansector and beyond, and emphasizes the need forhigh-quality in situ data recording of climaticparameters at Chagos.

CONCLUSIONS

The Chagos Archipelago is unquestionably avery valuable biological asset in an ocean showing

significant and continuing decline. The exceptionallygood condition of the Chagos marine ecosystems isimportant in terms of biodiversity and productivity,and for its likely biogeographic role in the ocean. Itsprotection is of great and increasing importance giventhat global pressures from overfishing and otheractivities resulting from human population growthare increasing. In this it joins a small handful ofother large, protected sites in the world (Nelson andBradner, 2010), and is the only one in the IndianOcean. The importance of the Chagos MPA wasfurther underpinned by a recent report across marinescience disciplines suggesting that the world’s ocean isat high risk of entering a phase of disturbanceunprecedented in human history (Rogers andLaffoley, 2011). Indeed, many more effective andvery large MPAs need to be created if internationalgoals for protecting the oceans are to be met,although the number of locations where this will bepossible is diminishing. Regarding terrestrial value,several smaller islands that were not ravaged bycoconut plantations remain intact and, by usingthem as source areas, much restoration is possibleand indeed has been commenced.

The MPA therefore is needed for multiplereasons. It has met with opposition from varioussources, including the oceanic fishing industry,the government of Mauritius that claims theterritory, and from Chagossians who were removedapproximately 40 years ago, and some of theirrepresentatives. While the decision to remove theinhabitants at that time was based on politics anddefence rather than for any reasons of conservation,the present good condition of such a large area hasbeen a fortuitous if unplanned consequence of thesubsequent lack of exploitation of the area. TheMPA was created ‘without prejudice’ to any futureresettlement, and if resettlement does occur thenmanagement must be adequate to avoid the problemswhich almost all past global experience hasdemonstrated could too easily happen.

The high value of relatively undisturbed areasencompassing a range of functionally linkedecosystems is becoming increasingly recognized atthe same time that their number world-wide isdiminishing (http://www.globaloceanlegacy.org/).Whereas there are many ‘managed’ reef siteselsewhere in the tropical oceans, almost all arethemselves in a poor condition compared withplaces like Chagos and a few Pacific sites. The‘shifting baseline syndrome’ (Pauly, 1995) appliesto marine management and in many places has ledto situations where decisions are taken that are

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highly disadvantageous to both the natural systemsand to the people dependent on them. Most reefsremain unprotected or protected in name only.The huge scale of the interconnected network ofatolls and banks in Chagos, and its effectivegovernance, are likely to become increasinglyimportant both directly and as a scientific referencesite in the Indian Ocean. BIOT has, at present andthe foreseeable future, governance which willenable this situation to persist. Priorities now aremanagement in an effective manner, whateverthe political future holds for the area, so that thebenefits of a well protected MPA are likely toextend to peoples and ecosystems far beyond theboundaries of the Chagos MPA.

ACKNOWLEDGEMENTS

The authors thank the Administration of the BritishIndian Ocean Territory for permission to visit thearea on various occasions, the military commandersand personnel for much assistance on site, and tothe officers and crew of the BIOT Patrol VesselPacific Marlin for exceptional help on all visits toatolls away from Diego Garcia. The OTEP fundprovided core funds for most visits, and all scientistsinvolved received funding from numerous sourcesto carry out their own programmes of work in thearchipelago. For assistance with genetic work wethank Jiddawi Norriman and Mohammed SuleimanMohammed (Zanzibar), and Nancy Bunbury(Seychelles).

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