Coral Reefs of the United Kingdom Overseas Territories

The United Kingdom (UK) governs, through its Dependent Territories, a total coral reef area of 4,712 km² making it, in jurisdictional terms, approximately the twelfth reef nation of the world, allowing for uncertainty in reef area estimates. Of the UK Overseas Territories, the reef nations include Anguilla, Turks and Caicos, Bermuda, the British Virgin Islands, the Cayman Islands, the British Indian Ocean Territories and the Pitcairn Islands. This national value is inferred from geomorphological inventory of the reef systems falling within these Territories, conducted using an internally consistent typology generated as part of the Millennium Coral Reef Mapping Project using Landsat 7+ ETM satellite images from the Caribbean, Indian Ocean and South Pacific regions. These Territories host the world’s largest atoll, the northernmost reefs of the Atlantic and the most easterly atoll of the Indo-Pacific reef province. In terms of main morphological units, atolls, banks, barrier reefs, fringing reefs and patch reefs are represented.

Anguilla lies at the northern end of the Leeward islands and is a mainly limestone platform with only a few extrusive basalts and tufts. The principal island is approximately 24 km × 5 km, and there several small outlying islets surrounding this. There is a fairly extensive reef system, particularly along the northern side, and there are a number of protected marine areas with coral reefs. The economy relies heavily on tourism which is increasing, as well as on financial services. Agriculture and fishing are not of major importance though the latter is driven by the increasing tourism, such that concerns exist regarding fisheries sustainability and the ecological impact of such activities on the coral reefs. Much of the shallow sublittoral is covered by seagrasses, algae and sand as well as reefs. On the southern coast, reefs are categorised as Acropora reefs, though these have degraded severely along with most similarly located shallow reef in the Caribbean, due to white band disease and probably hurricane activity also, such that today they are characterised by Acropora palmata rubble with relatively low diversity. Along the northern coast, similar rubble occurs, with several patches of live Acropora, but this area used to support vast areas of Montastraea spp also, and which likewise is in decline, probably from diseases. This area is degrading also, though not as severely to date. Overall coral cover has dropped from an average of 14 % in 1990 to 4 % in 2009. Changes to the management of Anguilla’s reefs (and other marine habitats) are long overdue in order to arrest or reverse these declines, and plans are in place to increase surveillance and enforcement capabilities of Governmental Departments.

The British Virgin Islands form the eastern edge of the Greater Antilles island chain, lying on a carbonate microplate located on a subsiding island arc. There are over 60 high volcanic islands with granite-like magma intrusions on which the present reefs have developed, on approximately 420 km of coastline. Marine habitats around the volcanic islands include seagrass meadows, muds, carbonate banks and coral reefs. Most reefs are fringing reefs which have developed on narrow shelves which average 500 m in width between low tide and the 20 m depth contour. Some coral cays exist also, a number supporting rich mangroves. Tourism has become increasingly important, and with it a shift occurred in the BVI from preserving natural resources for local subsistence to its exploitation for economic gain; one aspect of the tourism being development of the world’s largest concentration of charter yachts which, initially at least, severely damaged several reefs by extensive anchoring. Reefs also suffer from shoreline development, resulting in extensive damage around the main populated island. Environmental legislation that did exist did not keep up with the advancement of scientific knowledge, and updating legislation has since become a well-recognized need in the BVI, with some success, though resources are insufficient. As with many Caribbean locations, the white-band disease of Acropora, and the Diadema mortality, along with (more recently) warming episodes, have caused substantial degradation to the reefs of the BVI.

The British Virgin Islands has 14 declared protected areas in the marine environment. In addition, the ‘British Virgin Islands Protected Areas System Plan 2007–2017’ identifies another 40 areas for inclusion in the marine protected area (MPA) network, with designation in progress. The overall goal of the National Parks Trust of the Virgin Islands (NPTVI) was to create a network of marine protected areas that reflects the major marine and coastal habitats of the BVI, whilst protecting 30 % of the important biological habitats; to cluster protected areas together so that they can be easily managed; and to ensure that there are MPAs distributed across the BVI in order to ensure ‘resilience’ within the network. Network design utilised a mixed approach, with Marxan modelling, field assessment of marine habitats and stakeholder input.

Anegada is part of the British Virgin Islands, and is a low lying limestone island with a maximum elevation of 8 m. It has extensive salt ponds and wetlands. It is entirely different from the rest of the British Virgin Islands, US Virgin Islands and Puerto Rico which together form the Puerto Rican/Virgin Islands microplate. It formed as part of a massive coral reef system during the last Interglacial highstand 130,000 ± 2k to 119,000 ± 2k years before present. Its western side is comprised of dune and beach ridge complexes, lagoons and mangroves, known as the Anegada Ridge Plain Formation. The eastern side of the island is distinguished by the indurated coral reef limestone with modified karst topography including solution pits and sinkholes. Contiguous with Anegada is the Horseshoe Reef and together these cover approximately 133 km². The reefs have two distinctive facies, a high energy reef front along the north-eastern windward side of the island, and a series of patch reefs with a marked northwest/southeast orientation aligned to prevailing wind and waves on the southern leeward side. The width from shoreline to the reef crest varies widely, from 5 m to 3 km with a sandy lagoon with abundant seagrasses and algae. From the eastern tip of the island a barrier reef extends approximately 14 km southeastwardly to an area where the horseshoe shape of the reef turns almost 90 to the south. As with many reefs in the Caribbean, heavy mortalities of Acropora (and Diadema) greatly reduced live coral cover in the 1980s. The island has considerable resiliency and ability to adjust to both extreme events and prevailing conditions including, perhaps, those introduced by climate change. Although the coastline displays alternating areas of erosion and accumulation of sand with up to 300 m of change, the long-term result has been a counter-clockwise rotation of the western side of the island.

The three Cayman Islands of Grand Cayman, Cayman Brac and Little Cayman lie in the north-western part of the Caribbean Sea. All three are surrounded by a narrow shelf which acts as a base for the extensive development of coral reefs and lagoons. The shelf around each island has two gently-sloping terraces, a shallow one at 8–10 m depth and a deeper one at 15–20 m. The shallowest reefs, best developed around Grand Cayman and Little Cayman, are fringing reefs with an Acropora-Millepora thicket at or near sea level, behind which is a lagoon with a rubble zone, sands, patch reefs and grass beds. Seawards of the fringing reef is a barren rock pavement zone, succeeded by extensive development of coral reefs on the shallow terrace, where spur-and-groove structure is common, the spurs dominated by a coral assemblage of Diploria, Montastrea, Porites and Agaricia. A sand plain then leads to a second development of reefs at the edge of the deep terrace at about 20 m, beyond which is a steep drop-off down the fore-reef slope into deep water, to the limit of coral growth at about 70 m. Occasionally, as at Bloody Bay on Little Cayman, the deep terrace is absent and the drop-off occurs at the edge of the shallow terrace at 7 m as a spectacular, almost vertical wall.

The Cayman islands are three small low-lying subtropical islands in the NW Caribbean. The islands are tips of an underwater mountain chain and have a very narrow coastal shelf, usually of less than 1 km wide, which support considerable reef development. The major sublittoral habitats are coral reefs, lagoons, seagrass beds and mangroves, and fringing reefs shelter large areas of seagrasses and mangroves, the latter being important nursery areas also. There is a high diversity of marine invertebrates, with several molluscs and crustaceans providing commercially significant species. However, substantial recent developments have increased pressures on the marine systems, added to which more recently are stressors resulting from climate change. The islands are hit by hurricanes about once every 10 years, and suffer near-misses four times more often, which greatly affects these habitats. There are a number of different categories of Marine Protected Areas but even so, due to a number of direct anthropogenic stressors as well, coral cover has declined from 25 % to about 11 % over the past 15 years. Physical destruction from shipping and recreational boating has contributed significantly to this, as have various forms of pollution, dredging and shoreline construction, and poaching. The Marine Protected Area system is being reviewed, with specific measures to manage Grouper spawning aggregation sites, and a culling programme is underway in an attempt to control the invasive lionfish which pose the most recent threat to the coral reef fish communities.

Montserrat is a mountainous and heavily forested island in the Eastern Caribbean. Over the past 17 years the island has been dominated by an active volcano, which has changed both terrestrial and marine ecosystems. Unlike many marine habitats of the world where stresses are mostly manmade it has been the activity of the volcano that has had the greatest effects, and the areas has suffered far less from stresses created by man. Montserrat has varying underwater topography, areas on mostly untouched and unexplored reefs, and reef species that are healthy, abundant and uniquely located.

The Turks and Caicos Islands lie at the southern end of the Bahamas archipelago and comprise six major islands around the northern edge of Caicos Bank and two west of the smaller Turks Bank. The margins of these banks are defined by sharp drop-offs into deep water on all sides and are fringed by coral reefs, mainly on their windward (eastern) sides. There are six ecotypes comprising true (accreting) coral reefs: bank patch reefs, near-shore patch reefs, channel reefs, near-shore fringing reefs, platform margin bank-barrier reefs, and platform margin deep reefs. Hard-bottom non-reefal habitats that contain corals but are not true accreting coral reefs are also present. Near-shore fringing and bank-barrier reefs have their crests close to sea-level, with Acropora and Millepora as the main reef builders, and have lagoonal environments in their lee, while deeper reefs are dominated by the corals Diploria, Montastrea, Porites and Agaricia. The narrow platform margin is characterized by two terraces, the shallow terrace sloping gradually from either the shoreline or fringing reef to about 8–10 m depth, where there is an appreciable increase in slope to about 15 m depth, coinciding with the seaward edge of spur-and-groove structure, where developed. The deep terrace has a depth of 15–20 m and consists of a narrow sand plain with isolated patch reefs and/or low-relief spur-and-groove reefs, beyond which there is a steep drop-off into deep water.

The Bermuda islands and shallow platform lie on the top of an extinct Meso-Cenozoic volcano. The islands and the Bermuda Platform were created by reef building corals, vermetid snails and calcareous algae that colonized the eroding seamount. Coral reefs even played a significant role in the settlement of Bermuda and now human impacts of the well-populated islands are important to the ongoing health of the reefs and coral communities. The economic underpinnings of Bermuda – financial services and tourism, along with limited agriculture and small fisheries have created a society that has a moderate impact on the reefs and has a significant and direct economic interest in maintaining a healthy marine environment. Throughout the history of Bermuda, the distribution of coral reefs, and coral communities on the Platform have been determined by the interactions of several environmental factors. Pleistocene formations underlie many modern reefs and there is evidence of submerged reef tracts at depths below 60 m, all around the Bermuda Pedestal. The positions of these formations correspond to stable sea level positions attained during glacial and interglacial periods. Today, there is great variability in the marine environment on the Platform, with the most extreme conditions occurring in inshore waters. The most extensive reefs are developed around the shallow rim of the Platform and, seaward from this, down a gradually descending slope to about 50–60 m depth. Algal-vermetid cup reefs are particularly abundant in Bermuda. On the Platform, seagrass and calcareous green algae beds are closely associated spatially and ecologically with coral reefs, forming unique communities; these are widespread across the lagoon and larger inshore water bodies.

Bermuda’s reefs support populations of corals and fishes, derived from the Caribbean fauna, which show distinctive characteristics in regards to reproduction and growth. Bermuda’s corals and fishes have an attenuated summer and early fall reproductive season, that appears to be controlled by cool water temperatures in the winter and spring months. Reef fishes show a clear shift in reproductive output to the summer months compared to the winter spawning of many Caribbean conspecifics. Coral recruitment is dominated by brooding species (e.g. Porites astreoides) across all reef zones although framework species (Diploria spp; Montastraea spp) are common. Settlement and recruitment rates are comparable to Caribbean reefs. The recruitment of reef fishes has been studied intensively and both near-shore and lagoonal reefs appear to be nursery habitats for many reef fish families, perhaps substituting for the paucity of coastal mangroves in Bermuda. The strong seasonality of water temperature appears to reduce growth rates in both corals and reef fishes but may facilitate longevity. Many reef fishes attain greater sizes than conspecifics in the Caribbean. The patterns of distribution of corals, fishes and other reef taxa have been quantitatively assessed over the complex reef lagoon, rim reef and fore reef terrace and data incorporated into GIS databases.

As the most northern ecoregion within the Tropical Northwestern Atlantic biogeographic province, Bermuda’s reef biodiversity is a reduced complement of that found within the other ecoregions of the TNA. A characteristic of the Bermuda marine fauna is the absence of species otherwise ubiquitous in the TNA province (i.e., Acropora spp.). Notable differences in Bermuda’s species diversity is attributed to both geographic and physical forcing agents that include isolation, temperature, currents, bathymetric or coastal complexity, and environmental seasonality. Pleistocene sea level changes also may have been important to the development of Bermuda’s current diversity. Shallow-water scleractinian and octocorallian species diversity is currently considered well documented, however information is still lacking on the depth limits of many species, including in and extending beyond the mesophotic zone. The shallow-water azooxanthellate coral, Rhizopsammia bermudensis, is the only endemic scleractinian. Bermuda’s Symbiodinium diversity is comparable to the Caribbean in that clades A, B and C predominate in anthozoan hosts, but there is a notable absence of Clade D which has been recorded from several Caribbean conspecifics. In Bermuda, octocorals harbour only clade B. Most fishes in Bermuda have a western Atlantic distribution, but amphi-Atlantic and more widely distributed species are also common. High levels of genetic variation and unique Bermudian haplotypes have been determined for several species, spanning several higher taxa – not just cnidarians and fishes. Studies indicate that Bermuda’s marine populations are panmictic and self-seeding. Population connections with upstream reef systems have been inferred genetically for some but not all of the few species investigated. For Bermuda, population connectivity characteristics are so diverse, even among species with apparently similar reproductive and dispersal patterns, that best practices for management and conservation should be developed on a species by species basis.

The biodiversity of Bermuda’s coral reef fauna has been extensively studied by natural historians and taxonomic specialists since the mid- nineteenth century. Short taxonomic histories of the initial records and names of Scleractinia and Octocorallia found in Bermuda culminate in complete and up-to-date lists of the currently accepted species. There are 26 species of shallow-water azooxanthellate and zooxanthellate scleractinians, and 23 species of deep water azooxanthellate scleractinians reported from within the Bermuda EEZ; 25 species of shallow-water octocorallians and 33 of deep-water octocorals; and eight antipatharians. A few submersible explorations of the mesophotic zone and the deeper environs of Bermuda’s exclusive economic zone have revealed new species records for scleractinians, octocorallians and antipatharians. Recent and new records for six scleractinians, 24 octocorallians and 2 antipatharian species, presented in this review, include the first documentation of the scleractinian families Flabellidae, Stenocyathidae, and Turbinoliidae, the octocoral families Nephtheidae, Chyrsogorgiidae, Isididae, Keroeididae and Clavulariidae, and the antipatharian family Schizopathidae in Bermuda. Explanations are provided for confusion regarding records of Isophyllia rigida, Montastraea annularis, and Siderastraea siderea in Bermuda.

The Total Economic Value (TEV) of Bermuda’s coral reef reefs is based on 6 key ecosystem goods and services. These more tangible direct and indirect use values are: (1) Coral reef-associated tourism, (2) Reef-associated fisheries, (3) Amenity or reef-associated surplus value on real estate, (4) Physical coastal protection, (5) Reef-associated recreational and cultural values, and (6) Research and education value. The study area is estimated to be 400 km², encompassing the reefs of the Bermuda platform, excluding those of the outer edge of the North Lagoon. Quantification of each value, including data collection and decision-making, is summarized. The TEV of Bermuda’s coral reefs, dependent on the ecological integrity of the coral reefs and socio-economic conditions, ranges from $488 million to The Total Economic Value (TEV) of Bermuda’s coral reef reefs is based on 6 key ecosystem goods and services. These more tangible direct and indirect use values are: (1) Coral reef-associated tourism, (2) Reef-associated fisheries, (3) Amenity or reef-associated surplus value on real estate, (4) Physical coastal protection, (5) Reef-associated recreational and cultural values, and (6) Research and education value. The study area is estimated to be 400 km², encompassing the reefs of the Bermuda platform, excluding those of the outer edge of the North Lagoon. Quantification of each value, including data collection and decision-making, is summarized. The TEV of Bermuda’s coral reefs, dependent on the ecological integrity of the coral reefs and socio-economic conditions, ranges from $488 million to $1.1 billion per year, with a yearly average of $722 million, equivalent to 12 % of Bermuda’s GDP. The contribution of ecosystem services to this value are on average: (1) Tourism (US$406 million per year, or 56 % of TEV), (2) Coastal Protection (US$266 million per year, or 37 %), (3) Recreational and Cultural (US$37 million per year, or 5 %), (4) Amenity (US$ 6.8 million per year, or 1 %), (5) Fishery (US$5 million per year, or 0.7 %), and (6) Research and Education (US$2.3 million, or 0.3 %). Additionally, the Willingness to Pay extra by both cruise ship and air visitors, for ensuring the preservation of reefs per year is US$16 million. Four recommendations are given, focusing on (a) the use of TEV in policy interventions through improved legislation, integration of strategic environmental assessments (SEA), extended cost-benefit analyses, and damage compensation fees, (b) making use of the cultural importance of marine ecosystems to residents, (c) actively involving the tourism industry, and (d) strategizing spatial management and protecting critical marine areas..1 billion per year, with a yearly average of $722 million, equivalent to 12 % of Bermuda’s GDP. The contribution of ecosystem services to this value are on average: (1) Tourism (US$406 million per year, or 56 % of TEV), (2) Coastal Protection (US$266 million per year, or 37 %), (3) Recreational and Cultural (US$37 million per year, or 5 %), (4) Amenity (US$ 6.8 million per year, or 1 %), (5) Fishery (US$5 million per year, or 0.7 %), and (6) Research and Education (US$2.3 million, or 0.3 %). Additionally, the Willingness to Pay extra by both cruise ship and air visitors, for ensuring the preservation of reefs per year is US$16 million. Four recommendations are given, focusing on (a) the use of TEV in policy interventions through improved legislation, integration of strategic environmental assessments (SEA), extended cost-benefit analyses, and damage compensation fees, (b) making use of the cultural importance of marine ecosystems to residents, (c) actively involving the tourism industry, and (d) strategizing spatial management and protecting critical marine areas.

Ascension Island lies 8° south of the equator in the South Atlantic and approximately 150 km west of the mid-Atlantic Ridge. The island has a stark beauty, with much of it resembling what one might imagine a martian landscape to look like: rugged brown lava flows and little vegetation. In spite of its tropical location, the island does not have palm-fringed shores nor does it have coral reefs – but why? Just five species of scleractinian coral have been identified, though these are either encrusting or solitary forms. Reasons for the paucity of marine invertebrates in the island’s near-shore waters are put forward, including the island’s isolation, the influence of oceanic currents affecting colonisation and the heavy grazing pressure from fish and sea urchins.

The British Indian Ocean Territory consists of the Chagos archipelago, almost all of which was designated a no-take MPA in 2010. It covers 650,000 km², with >60,000 km² shallow limestone platform and reefs. This has doubled the global cover of such MPAs. It has strong biological affinities with the western Indian Ocean, and larval travel time to reefs to the west of it is 25–35 days. Genetic work is only recently commencing, but it is likely to be a cross-roads, or bridge, in this respect. A licensed fishery used to exist, but this too was closed in 2010, and the large diameter of the area may prove to be a significant reserve for pelagic fishes such as tuna also. The region probably contains about 300 sea mounts and knolls, which is about 10 % of all Indian Ocean seamounts and nearly half of all those protected worldwide, and so the area is regionally important for these features as well with their unexplored but probably diverse deep benthic and fish biota. The area is also well placed to fill a large gap in global monitoring systems; it is located in key region of climate variability, so programmes carried out there are particularly important to research into climate change effects also. The area has very high conservation value and is an important biological asset in an ocean where most reefs show significant and continuing decline in health.

We assess the status and structure of coral reef fish assemblages in the large remote and unfished Chagos Archipelago, comparing fish biomass and structure among atolls and across the wider western Indian Ocean. We then assess the longer term trends in reef shark abundances and the stability of fish assemblages through the 1998 climate induced habitat disturbance. Diego Garcia atoll had the lowest standing reef fish biomass estimates, while Peros Banhos and the Great Chagos Bank had the highest. Further, the biomass of larger bodied, higher trophic level, and most fishery target families was higher in the northern atolls, indicating a potential impact of the recreational fishery operating around Diego Garcia. Fish biomass in the northern atolls of Chagos was up to six times greater than estimates from even the more successful small marine protected areas elsewhere in the western Indian Ocean region. Interestingly, the biomass recorded around Diego Garcia was comparable to the highest values reported elsewhere in the region, suggesting that although the recreational fishery has had some impact at that atoll, it is far from overfished. Reef shark abundance has declined substantially since the 1970s, largely due to illegal fishing activities, however the numbers recorded in 2010 and 2012 were higher than those recorded in 1996 and 2006. The 1998 mass coral bleaching event did not have a major impact on reef fish assemblages in Chagos, with specialised coral feeding fishes being numerically dominant over less specialised coral feeders by 2012. The Chagos Archipelago provides an example of the biomass and community structure of reef fishes that many reefs likely had in the past, and also demonstrates the considerable resilience that coral reefs can exhibit when they are not otherwise stressed by chronic human pressures.

A broad range of chemical contaminants and pollutants have been measured within the Chagos Archipelago. Contamination is amongst the lowest in the world. Whilst much data is in the open literature, the chapter also includes details of extensive pollution monitoring for the atoll Diego Garcia which hosts a military facility. Hydrocarbons present are primarily of a natural origin with negligible evidence of contamination from petroleum or combustion origins. Tar balls, however, have been reported on several beaches in the Archipelago. Analyses of faecal steroids provide negligible evidence of sewage contamination. ‘Persistent organic pollutants’ (POPs), including PCBs and pesticides, were generally below analytical detection limits, as were polyfluorinated compounds, brominated, chlorinated and organo-phosphorous flame retardants, fluorinated tensides, and surfactants (PFOS). Antifouling biocides and herbicides in Diego Garcia show negligible contamination. Metal concentrations are very low. Levels of most contaminants are typically comparable to those recorded in environments perceived to be pristine, for example, the Antarctic. In Diego Garcia, extensive monitoring includes regular analyses in accredited US laboratories of over one hundred metals and organic contaminants. Results generally reveal concentrations below detection limits. This is in agreement with the open literature surveys. These legislated assessments are designed to ensure both environmental and human health preservation. Whilst many detection limits are higher than those of the independent surveys, they generally confirm the pristine nature of the Archipelago. Beach surveys, however, revealed a surprisingly high number of pieces of debris throughout the Archipelago, mainly plastics of South East Asian origin. The number of litter pieces in Diego Garcia was less than in the other atolls, reductions being attributed to beach clean-up events. Microplastic contamination is shown to be both widespread and relatively high compared to other locations on a global scale, and there were significantly more microplastics at uninhabited atolls compared to the Diego Garcia, showing the potential for microplastics to accumulate in remote locations. Holothurian (sea cucumber) poaching has been another significant environmental pressure on the coral reefs of Chagos and is included in this review, in view of the reported ecological benefits of the group to reef health and resilience.

The Pitcairn Islands are a group of four near-pristine small islands which can claim to be some of the most remote islands in the world. Pitcairn, with a land area of just 4.5 km², is the only inhabited island of the four and has a population (in 2011) of about 60. The islands are located in the crystal-clear waters of the central South Pacific at the south-eastern extreme of the Indo-West Pacific biogeographic province. Each island forms the visible tip of a massive, though extinct, submarine volcano, with between 120 and 200 km separating each. The diversity of nearshore marine species around the four islands is low when compared to island groups lying to the west, a fact reflecting the islands’ low latitude (between 24° and 25° S), their isolation, the limited range of habitats and that colonisation has been largely from the west, despite the islands being upwind and upstream of these biologically rich source areas. A total of 87 scleractinian coral species have been recorded from the islands to date (of which 29 belong to the family Acroporidae), together with 353 species of reef fishes (19 Chaetodontidae), 64 species of echinoderm and just over 500 species of mollusc. The islands’ coral reefs do not suffer from the usual threats associated with human interference, largely on account of their isolation; indeed, the islands remain one of the most pristine marine environments in the world. Their nearshore waters have escaped the ravages of modern fishing methods and the degradation often associated with coastal industries. This has led to the Economic Exclusion Zone around the islands being presently considered as becoming a highly protected marine reserve, one of the largest such reserves in the world.