Coral Reefs of Anguilla

Abstract

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.

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Introduction

Anguilla (18°12.80N and 63°03.00W) is the most northerly of the Caribbean Leeward Islands. It is a low lying coralline Iandmass approximately 24 km long. Its central portion, at its widest point, has a width of approximately 5 km, tapering off rapidly towards easterly and westerly ends (Fig. 2.1). Most of it is a limestone platform (Fig. 2.2), with Crocus Hill, at an altitude of 65 m, being the highest point above sea level. The surrounding shallow platform, the Anguilla bank, is the most northern formation of the Lesser Antilles, separated from the Greater Antilles by the Anegada Gap. These islands and shallow substrates are based on a much larger limestone platform which is contiguous with several adjacent islands, most notably St Martins (Hubbard 1989). Anguilla has only a very few small extrusive basalts and tuffs, and thus contrasts strongly with adjacent islands which include substantial volcanic structures which emerge through the limestone to several 100 m high. A long chain of submerged shallow water off the northern side of Anguilla provides much substrate for reefs and for huge expanses of sandy substrate. This covers a total of about 14,600 ha of sublittoral substrate less than 20 m deep.

Fig. 2.1

Map of Anguilla. The main ‘ecologically based’ marine protected areas. Three other areas afforded protection are not illustrated: Sombrero Land/Sea Reserve, Junks Hole Marine Park, and Rendezvous Bay (Photograph S. Wynne)

Fig. 2.2

Limestone cliffs along the northern coast of Anguilla (Photograph S. Wynne)

Aside from mainland Anguilla there are a number of offshore cays and rocky outcroppings, the most significant being Sombrero Island, Dog Island, Scrub Island, Prickly Pear Cays, Sandy Island, Anguillita and Scilly Cay (Fig. 2.3). Various protected areas are present in Anguillian waters whose purposes vary from preservation of historical sites to conservation of reef and seagrass areas. Table 2.1 gives details of these protected areas, and baseline surveys of the ‘ecologically based’ marine parks (see Fig. 2.1) were conducted in 2007 where 30 sites were surveyed as part of a project funded by the British Government through the Overseas Territories Environment Programme to increase the efficacy of the management of these areas(Wynne 2007a). In general the majority of Anguilla’s underwater habitat consists of coral reefs, seagrass beds, sand and/or algal flats. A detailed atlas of these habitats was produced in 1994 by the Natural Resources Institute of the United Kingdom (NRI 1995; Sheppard et al. 1995).

Fig. 2.3

Typical small islands around the main island of Anguilla: Scilly Cay in the north (Photograph S. Wynne)

Table 2.1 Details of Anguilla’s marine protected areas. It should be noted that at the time of writing legislation for these areas is limited although this situation is poised to change in the next few years

Economy and Services

The Valley is Anguilla’s capital and the only true ‘town’ on the island with a population of 1169 (2001 Census). Other settlements on the island overlap onto each other and as such their names relate more to geographical locations rather than ‘villages’. All main services are based in The Valley, for example post office, Government buildings, hospital, library, as are most shops, banks, schools and telecommunications. Anguilla’s economy relies heavily on tourism, a sector that began expanding rapidly during the 1980s. Prior to this only a few 1,000 foreigners visited the island annually, but by the end of the following decade visitor numbers were estimated to be up to 80,000 per annum (Gell and Watson 2000). The other important economic sectors are financial services, construction and Government services. In terms of dollar value other sectors such as agriculture and fishing are not of major importance. Aside from local demand the fishing industry is driven by the increasing tourist sector and concerns exist regarding fisheries sustainability and the ecological impact of such activities on the extensive coral reefs that surround the island.

Fishing Industry

Thirty years ago, Olsen and Ogden (1981) estimated the maximum sustainable yield (MSY) for demersal stocks to be 2,740 t for finfish and 230 t of lobster and 230 t of conch and other shellfish, with 80% of the production potential coming from the 22% of the shelf area containing coral reef communities. Nearshore resources by 2000 had declined under increasing pressure (Gell and Watson 2000). Export duties allowed an estimate of lobster exports in 1979 of at least 28,364 kg, though the true value was probably much higher. In 1980, fishers were discarding scarids and snappers up to 2.3 kg as trash fish and fish pots used Epinephelus striatus, now commercially extinct in many parts of the Caribbean, as lobster bait (Salm 1980). However, by 1987, signs of overfishing were apparent for lobster and potfish (Stephenson 1992).

Today, Anguilla’s fishing industry is largely artisanal with the majority of fishers owning one small open vessel powered by outboard engines (average length 7.4 m) and employing only one other crew member. There are two main target groups, lobster and finfish, which are geographically separated and serve distinct markets. There is also a small conch fishery present. The finfish fishery, in terms of total weight, accounts for approximately 67% of landings, and although most is sold locally some fishers do sell their catch in St Martin. Hotels & restaurants in Anguilla generally purchase deep demersal and offshore pelagic species along with the majority of lobster landings, whereas demand for home consumption is largely for reef species. This essentially means pressure on Anguilla’s coral reef systems is driven mainly by local demand for food, not tourism. An exception to this is the small ‘crayfish’ fishery (Panulirus guttatus, a species closely related to Panulirus argus, the main lobster species targeted) that is harvested in shallow reef areas. In 1999 it was estimated that c.4.5% of the population was employed in the fishing industry, an industry that in 2006 provided only 1.4% of the islands GDP (XCD 6.11 million). There are plans to encourage fishers to move towards large (offshore) pelagic species, which at present are mainly the target of the sports fishing industry. This would relieve pressure on reef resources and also satisfy the growing tourist market which generally favours the bone-free fillets that these species provide. Reef fish comprise an estimated 53% of landed catch (Fig. 2.4), with typical composition as detailed in Fig. 2.5. Data collected as part of the 2007 fisheries census suggested that there are currently around 300 fishers operating in Anguilla (Murray 2008). However, recreational fishing in Anguilla is a popular past-time with most people partaking in it at some point in their daily lives. Spear fishing (by locals) is currently permitted in all parts of Anguilla’s marine environment and is a popular past-time for many islanders. It is likely though that due to its highly efficient nature, management measures will be introduced in the near future to limit its impact.

Fig. 2.4

Composition of landings made by Anguilla’s fishing industry split into the six main target groups (Murry 2008) (Photograph S. Wynne)

Fig. 2.5

Family composition of reef fish caught by local fishers. Data collected via interviews during 2009 (provided by Professor Nancy Carder). These results have been used rather than those presented by Wynne (2010) as they represent what the fishers caught rather than what they landed. Parrotfishes for example are often used as bait and so, aside from rarer large individuals, do not get brought ashore (Photograph S. Wynne)

Coral Reefs

Much of the shallow sublittoral in Anguilla supports seagrass beds and expanses of sand and algae, as well as reefs. As far as its reefs are concerned, Anguilla is surrounded by a mixture of fringing, barrier and patch reefs interspersed by the sand/algal flats and seagrass beds. Shallow, sheltered habitats support large areas of seagrasses, mostly of extensive shallow beds of Thalassium testudinum (turtle grass) with some deeper beds of Syringodium filiforme (manatee grass), and coral reefs intersperse with these (Gell and Watson 2000). On the whole the reefs exist in shallower regions although there are areas of extensive deeper reefs beyond recreational dive limits. In the 1970s coral communities cover approximately 22% of the entire Anguillan shelf area (Olsen and Ogden 1981). In general the reefs around Anguilla can be split into two geographical regions: the northern coastal region and the southern coastal region.

Southern Coast

The southern coastal region, at least historically, can be categorised as an Acropora sp. dominated fringing reef system that is ecologically and structurally influenced by its exposed nature. Although historical data are lacking, this system appears to have degraded severely since the early 1980s when it was reportedly still in a relatively pristine condition. Exact reasons for this demise are unclear but hurricane damage during the 1980s (and later in the 1990s) had a severe effect, and White Band Disease that is known to have been affecting Acropora sp. throughout the region at the time, had also severely affected Anguilla by the 1990s (Sheppard et al. 1995; Bythell and Buchan 1996). The reefs simply did not recover after these events and in most shallow reef areas which exhibited classical elkhorn reef structures, the coral cover was essentially dead (Sheppard et al. 1995) (Fig. 2.6). Currently the south coast reef areas are characterised by Acropora palmata rubble with very low benthic diversity or low relief rocky pavement areas with scattered soft corals, macroalgae, sponges and small hard corals (for example Montastraea sp., Diploria sp., Siderastrea sp. & Agaricia sp.). Some relatively extensive seagrass beds also exist along the south coast.

Fig. 2.6

Skeletal Acropora reef on the south coast of Anguilla (Photograph S. Wynne)

Northern Coast

The northern coastal region is dominated by patch, barrier and fringing reef systems interspersed by sand and/or algal flats, with a combined estimated area of 14,600 ha (Sheppard et al. 1995). In a similar way to the south coast it appears that historically there were extensive Acropora sp. reefs that exist today mainly as vast rubble fields. Having said this, a few patches of intact Acropora palmata stands can still be found along the Seal Island reef system, much of which appears to be new growth, and large expanses can be found of Porites also (Fig. 2.7).

Fig. 2.7

Extensive colony of Porites off Sandy Island, North coast (Photograph S. Wynne)

Although much reduced today, vast areas of Montastraea spp. were also known to have been present historically in northern coastal regions. This genera is still the most dominant in the area but of the existing colonies many are exhibiting signs of disease (mainly Yellow Blotch Disease) which is probably the cause of its overall decline (see Fig. 2.8). Although northern reef areas appear to be slowly degrading, it does not appear to be as severely affected as the south coast, with extensive areas of relatively high diversity still present (albeit with high levels of macroalgae). This diversity still extends to the hard coals with dominant genera being Montastraea sp., Diploria sp., Siderastrea sp. & Porites sp. As with south coast reef systems, reasons for the degradation of the northern reef system are likely a mixture of stressors that probably interact with each other in complex ways. For example, climatic factors such as hurricanes and bleaching physically damage corals that then find it difficult to recover because (for example) eutrophication encourages disease, and macroalgae is more able to dominate in their place. Grazing species become less able to keep the macroalgae under control, a problem that is exacerbated by reduced densities of Diadema antillarum since the mass mortality event in the 1980s (Tuya et al. 2004) and by overfishing of herbivorous fish species. All of this ultimately leads to habitat degradation.

Fig. 2.8

Montastraea annularis infected by Yellow Blotch Disease in Shoal Bay East, Anguilla (Photograph taken by S. Wynne in June 2007)

In 1994, overall 435 ha of dead elkhorn reef was mapped in Anguilla, much of it located across the entrances to bays and off several sheltered beaches (Sheppard et al. 1995). It appears that other than some renewed growth in some areas, most remains as areas of rubble.

Temporal Changes

Most reports suggest Anguilla’s reef systems have been in decline since before the 1980s although data to back this up are sparse. The extensive mapping study in 1994 showed that large expanses of the shallow elkhorn (Acropora palmata) was dead, most likely due to White Band Disease (Sheppard et al. 1995). A study investigating the impacts of hurricane Luis in 1995 (Bythell and Buchan 1996) compared Anguilla to the British Virgin Islands and concludes that its reefs had ‘undergone extensive mortality of the dominant coral Acropora palmata’ since they were first affected by White Band Disease in 1976. The earliest marine ecological survey work conducted in Anguilla was undertaken by the Bellairs Institute (Barbados) who conducted reasonably extensive survey work in 1990 (Oxenford and Hunte 1990). Since 2007 annual monitoring began (see following section), and in 2009 a dedicated study was also conducted that attempted to revisit the sites used by the Bellairs Institute in 1990 (Wynne 2010). Although these sites were established pre-GPS a number of them were relocated and surveys replicated. The comparative study revealed that over the last 20 years both hard corals and reef fish populations have declined (although there is some variability between sites). Combining all the sites, coral cover has dropped from an average of 14% in 1990 to 4% in 2009. This is a 70% decline in less than 20 years. At one site close to Forest Bay the decline was as high as 98%. Overall, reef fish populations have dropped by approximately a third. The 1990 study did not record fish size so biomass estimates are not possible. This situation is of significant concern because, even though White Band Disease reportedly began to affect Anguilla’s reef systems in 1976, the Bellairs study concluded that in 1990 there were a ‘variety of diverse and attractive marine habitats (which are) in relatively good condition, with little apparent impact from human activities’. This certainly does not seem to be the case today. On a positive note, macroalgae levels were more variable since 1990 with some sites showing an increase while others showed a decrease. Reasons for this remain unclear but it is likely that it is at least in part thanks to a partial recovery of Diadema antillarum since the mass mortality event in the 1980s. Although some areas of reef still have very limited numbers present others appear to be recovering and have very high densities.

Present Monitoring

In 2007 the Department of Fisheries and Marine Resources initiated the Anguillian Marine Monitoring Programme (AMMP), a long-term project annually assessing key sites within Anguilla’s shallow marine environment. The surveys at these sites were in areas that did not exceed 15 m in depth. In the first year five sites were surveyed as part of a pilot study (Wynne 2008a) that tested methodology and served to train research staff. Over the following years more sites were added to the programme (Wynne 2008b), so that by 2010 the full complement of 15 sites had been reached. Ten of these sites were located on coral reef areas and five on seagrass beds. At the ten coral reef sites full benthic surveys are conducted annually using SCUBA equipment, together with fish counts that assess total species diversity and size class/abundance of commercially and ecologically important families. Full survey methodologies can be found in Wynne (2007b). At the ten sites surveyed hard coral cover ranges from almost 15% to less than 1% and macroalgae cover ranges from almost 30% to less than 1% (Table 2.2). Coral diseases at the monitoring sites are sometimes relatively common and can affect more than 50% of colonies present (Table 2.3). The most prevalent diseases are currently yellow blotch disease infecting Montasraea sp. (see Fig. 2.8) and cyanobacterial overgrowths/infections affecting a variety of species but most noticeably Siderastrea siderea. White Band Disease is not often recorded but this is likely due to the current paucity of Acropora palmata.

Table 2.2 Percentage covers of main benthic characteristics of the ten coral reef sites monitored as part of AMMP. Results are for all surveys combined between 2007 and 2009. For individual results see Wynne 2008a, b and Wynne 2010. Other benthic characteristics not detailed include (but are not limited to) sand, calcareous algae and mobile invertebrates

Table 2.3 Coral health results across the ten coral reef sites monitored as part of AMMP. It should be noted that the sites that have the highest percentage of corals 100% healthy also have the lowest percentage cover of hard corals (Table 2.2)

Across the ten reef sites surveyed the five most abundant fish species were Thalassoma bifasciatum (1,240 ha⁻¹), Acanthurus coeruleus (867 ha⁻¹), Acanthurus bahianus (840 ha⁻¹), Scarus iserti (787 ha⁻¹) & Chromis multilineata (413 ha⁻¹). The abundance measure is mean number of individuals per hectare of available habitat, i.e. that representative of the study sites. Of the commercially and ecologically important fish families surgeonfishes (Acanthuras sp.) are the most prolific followed by parrotfishes (Scarus sp. & Sparisoma sp.). Mean results for all families included are in Table 2.4, and the mean size class of these fish families is 10–15 cm (Fig. 2.9) in terms of relative biomass. This measure is a simplified method of calculating biomass based purely on length of fish.

Table 2.4 Percentage of total number of individuals within each size class across all surveyed reef sites split into commercially and ecologically important fish families

Fig. 2.9

Percentage of relative biomass that each size class of all commercially and ecologically important fish families accounts for across all surveyed reef sites (Photograph S. Wynne)

The current monitoring effort has concluded that Anguilla’s shallow (<15 m) coral reef systems are in a relatively poor state of health with low hard coral cover, high macro algae cover and smaller than expected mean fish size classes. The corals that are present are threatened by numerous factors including (but not limited to) disease, climate change, overfishing of various fish species and organic pollution. These threats are difficult to separate as they are all interlinked, and difficult to manage as their sources can be numerous and often outside management areas. For example, although organic pollution can be derived from numerous local sources (yachts illegally dumping grey water; leeching from poorly maintained septic tanks; and salt ponds, a natural sink for organic nutrients, being connected to the sea – either anthropogenically by pipes or naturally via storm breaches) it is likely that the pollution is predominantly influenced by regional factors, for example heavy nutrient loads introduced into the Caribbean Sea via the Orinoco outflow. Despite this, local management is essential where possible as it will only be through all nations doing whatever they are able that the regional influences may be mitigated.

Lionfish

During the latter part of 2009 the Department of Fisheries and Marine Resources lead a public awareness initiative to inform people of the pending arrival of the invasive Lionfish (Pterois volitans), and also laid out a targeted eradication response plan (Wynne 2009) that would be initiated once their arrival had been confirmed. This confirmation came on the 16th August 2010 when a local dive operator spotted an individual close to Anguillita Cay. A few days later the specimen was captured by Fisheries Officers, photographed, and brought ashore for positive identification. In the months that followed sighting frequency began to increase and by the end of the year ‘permanent arrival’ had become a reality. Government effort is being targeted at bathing beaches and important reef areas, with future monitoring and reports by the public tracking their spread and impact. It is likely that this invasive species will unfortunately become another threat to Anguilla’s coral reef ecosystem and as such new management measures are needed to mitigate its impact. These measures will be all the more urgent as with no known predators in the Caribbean this species can decimate juvenile fish populations and negatively affect local livelihoods. The Department of Fisheries and Marine Resources currently issues ELF capture devices to dive operators to help safely target this venomous species.

The Future

Changes to the management of Anguilla’s marine environment are long overdue, and results from current monitoring combined with the arrival of the Lionfish mean these changes are now more urgent than ever. Indeed, plans are afoot to bring in a number of new management measures that are designed to promote the sustainability of Anguilla’s marine resources, including its coral reefs. Plans include (but are not limited to) restricting spearfishing, the introduction of closed seasons, and enhanced management of the Marine Parks to include areas closed to fishing. The mention of such plans has already come up against public resistance, and until this matter is addressed any management strategy will likely fail. With this in mind the present focus is on public outreach, and a programme of educating stake holders so that they understand why management measures are being introduced and the benefits that they will receive in the long term. Plans are also in place to increase surveillance and enforcement capabilities of Governmental Departments through officer training workshops and the overhaul of the present Fisheries Department vessel.