The Reefs of the Turks and Caicos Islands

Abstract

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.

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Introduction

The British Overseas Territory of the Turks and Caicos Islands lies at the southern end of the Bahamian archipelago in the tropical north-west Atlantic between 21° and 22°N and 71° and 72° 30″ W (Fig. 9.1) The territory itself is made up of three separate carbonate bank systems: the Caicos Bank, the Turks Island Bank and the Mouchoir Bank. The larger Bahamian archipelago includes territories of three countries: The Bahamas, the Turks and Caicos Islands and the Dominican Republic. All of the land areas in the archipelago are part of the Bahamas or the Turks and Caicos Islands, but the Dominican Republic claims the submerged coral reefs of the Silver and Navidad Banks at the extreme southeastern extent of the chain (Sealey 2006)

Fig. 9.1

Map of the Bahamian Archipelago showing islands, banks and deeps, with TCI and major passages shown at southern end of chain (Google Earth)

The Turks and Caicos Islands (TCI), along with the rest of the Bahamian archipelago, are characterized by clear, shallow waters overlying white carbonate sands. The banks cover about 90%, with the exposed landforms (islands) comprising only about 10%, of the area of the banks (Table 9.1). Each bank system is characterized by low-lying islands that are the result of high carbonate production, cycles of low and high sea level, and prevailing winds. The largest bank, Caicos Bank, has six major islands (West Caicos, Providenciales, North Caicos, Middle Caicos, East Caicos and South Caicos) arranged sequentially in an arc along the northern platform margin (Fig. 9.2). The smaller Turks Bank has two islands (Grand Turk and Salt Cay) situated on the western side of a much smaller platform. The two shallow carbonate banks are separated by a deep passage, the 35 km-wide Turks Island Passage, which reaches depths of 2,200 m, while the Caicos Bank is separated from Mayaguana Island and the southern Bahamas islands of Great and Little Inagua by the 70 km-wide Caicos Passage with maximum depths approaching 4,400 m. The Turks Islands are separated from the Dominican Republic and Haiti to the south-east by the Mouchoir and Silver Bank Passages. The margins of these banks are defined by sharp drop-offs into deep water on all sides and are fringed by coral reefs, particularly on the seaward side of the Caicos Islands. The coral habitat includes two major groups: true coral-dominated accreting reefs and hard-bottom non-reefal habitats that contain corals but are not accreting coral reefs.

Table 9.1 Bank and Island Areas and Perimeters of the Turks and Caicos Islands: Area of the shallow banks and island areas are given in square kilometers. Bank perimeters and island shorelines are given in kilometers. The total shallow water bank area includes from the shoreline to the 200-m bathymetric contour. Land areas include the area of coastal mangroves, but not large creeks and bights

Fig. 9.2

NASA Space Shuttle image STS050-82-98, 1992 (modified) of Caicos Bank with major islands identified. Turks Bank and islands not shown

In this chapter we give a general description of the carbonate bank geology, reef geomorphology and zonation, known biotic communities, coral reef fish and fisheries, marine parks, and assessments of reefs as related to anthropogenic and other threats. TCI is the least prosperous territory, and has the smallest population compared to other western Atlantic British Overseas Territories (Anguilla, Bermuda, Cayman Islands, Montserrat, and British Virgin Islands), but has the largest shallow water marine resources, including reefs. The chapter concludes with a short overview of the governance and regulatory structure that impact reef management within this island microstate.

Some of the first overviews of the coral reefs of the Turks and Caicos Islands were given by Wells (1988) and Koltes (1993), the latter based on one of the first coral reef research field stations established on Grand Turk. Since then there has been a paucity of synoptic quantitative studies on the reefs, as much of the area is inaccessible except by boat. Quantitative studies have been carried out in association with fisheries assessments, regional assessment of reefs or placement of marine parks (see Medley and Ninnes 1999; Gaudian and Medley 2000; Tupper and Rudd 2002; Dikou et al. 2009). Much of the field research has been carried out on the south-eastern side of South Caicos and nearby Long Cay at the School for Field Studies station on South Caicos (Sullivan et al. 1994, 1996; Chiappone et al. 1996; Steiner 1999; Dikou et al. 2009). Research has also been carried out on commercial SCUBA diving boats that operate around the banks, both as live-aboard and shore-based dive tours (Spotte et al. 1994; Schelten et al. 2006).

Geography and Geomorphology of Reefs

As previously mentioned the Turks and Caicos Islands form the southern extent of the Bahamas Archipelago which stretches from the Turks Islands north-west to Little Bahama Bank. The islands and banks of the islands are geographically, geologically and ecologically part of this single archipelago (Enos 2011), with Pleistocene carbonates, often in the form of oolites and eolianites, providing the foundation for Holocene reefs and sediments. Rankey et al. (2009) studied Holocene and Pleistocene shallow marine carbonates from Providenciales in the northwestern part of the Caicos Platform, using sedimentology, bottom observations, remote sensing and sub-bottom profiling. They conclude that such northeast-facing platform margins exhibit considerable facies variability and show the best developed reefs where wave-dominated conditions from the open Atlantic prevail. Furthermore, buried top-Pleistocene bedrock configuration appears to exert a strong control on the Holocene morphology of the reef complex in the study region. Differences between the carbonate bank systems are perhaps the most important aspect in describing the reef ecology of the archipelago. Classification of the carbonate bank environment is based on geomorphology, energy exposure and bank size, with a strong latitudinal gradient. The areas of banks and islands included in the territory are shown in Table 9.1. The Turks and Caicos platforms form a small part at the southern extent of a much larger geological and ecological system. The entire archipelago experiences a tropical dry climate, with the Turks and Caicos as the hotter and drier southern extreme. The archipelago stretches over 7° in latitude (1,270 km) and extends north-westwards from the tropical dry islands of the Turks and Caicos Islands to the subtropical Abacos, all influenced by frontal systems from North America. Bank systems, and their associated islands, are the fundamental components of biodiversity in the archipelago. There is roughly a 10:1 ratio of marine bank to terrestrial island areas in the archipelago (Table 9.1). The bank perimeter includes only platform margin length. The platform margin is characterized as the area of barrier and fringing reef growth, upwelling and sediment transport events critical in marine faunal distributions. The length of shoreline can be much larger than bank perimeter length due to convolutions and embayments on many of the islands. Near-shore reef features include patch reefs, non-reefal hard bottom and fringing reefs. The dry, tropical climate of the archipelago means there are no surface water resources, and no river run-off or sedimentation, resulting in extremely clear water, facilitating coral growth near the shore.

The sheltered banks, such as Caicos Bank, are dominated by long, often narrow, islands that stretch along the northern and eastern platform margins. The islands separate high energy, wind-blown environments along their eastern shore from protected coastal wetlands and beaches along the western shores. A typical island thus provides a barrier to wave energy, and creates extensive soft sediment habitats in its lee to the west. Caicos Bank is characterized by well-developed exposed reefs along the eastern platform margin (Fig. 9.3). The fully-exposed banks, like Turks and Mouchoir Banks, lack islands along the eastern platform margin, and are characterized by deep (mesophotic) reefs, patch reefs, and fringing reefs along very low-lying islands. The large tropical shallow-water marine environments of the Turks and Caicos banks support a wide variety of reefal systems, both true accreting coral reefs and non-reef coral habitats. The geomorphic classification of these reefal areas used here generally follows the published classification schemes of Mumby and Harborne (1999) and Andrefouet (2008).

Fig. 9.3

Distribution of reefs on the Turks and Caicos banks (From REEFbase GIS 2012)

The prevailing trade winds are from the east and north-east, resulting in rough seas on the east side of Caicos Bank but generally calm seas on the west side (Wells 1988). Reefs fringe the platform on the windward side of its eastern and north-eastern islands and on the leeward side of its northern and western islands (Steiner 1999). Hurricanes occasionally visit the islands from June to November (Gaudian and Medley 2000). Air temperatures average 25 °C in winter and 29 °C in summer, with concomitant surface water temperatures ranging from 22 °C in the winter to 28 °C in the summer. The islands of the Turks and Caicos are at the eastern edge of the wider Caribbean Sea, and experience unequal, semi-diurnal microtides. The tides are less than 1.5 m in amplitude, and there are two high tides and two low tides each day. The semi-diurnal tides create strong currents through channels and move water on and off the carbonate platforms. Salinity and temperature variability on the banks are thus impacted by radiative heating and evaporation (Buchan 2000).

The dry, tropical climate was historically (and continues to be today) attractive for solar evaporative production of salt. Perhaps the greatest ecosystem-wide changes to the islands occurred with the establishment of salt ponds on South Caicos, Grand Turk and Salt Cay in the eighteenth century with the salt trade (see the Turks and Caicos National Museum website for overview). In fact, historical uses of marine resources and land have likely led to significant changes on the coral reefs, starting with the occupation of Tiano Amerindians beginning some 700 years prior to the arrival of Columbus (Keegan et al. 2008; Sinelli 2010). Seals, turtles, seabirds and near-shore fauna were removed from areas of human occupation. Europeans followed with the deforestation and removal of mangrove wetlands on the small islands to facilitate solar salt production which became the basis of the colonial economy.

Coral Habitats and Reef Topography

Islands tend to occur at the platform margin, a narrow fore-reef shelf gradually sloping to about 20 m, with a steeper drop-off to 200 m depth. This is particularly well shown in the crescent of islands from West Caicos to East Caicos. The 20 m isobath approximates the transition from shallow to deep water, where slopes steepen to 45° or more at the edge of the platform margin. The shelf averages about 400 m in width but increases to over 9,000 m off the southeastern margin of the Caicos Bank. The narrow shelf, protected by islands, supports the true accreting reef communities in the Turks and Caicos banks. Coral reefs occur as patch reefs, fringing reefs, and bank-barrier reef systems most extensively on the larger Caicos Bank, but also on the Turks Bank.

The platform margin is characterized by two gently-sloping terraces. The shallow (or upper) terrace slopes 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 development, where present (Steiner 1999; Rankey and Reeder 2010). The deep (or lower) terrace has a depth of 15–20 m and consists of a narrow sand plain with isolated patch reefs or low-relief spur-and groove reefs, beyond which is a steep drop-off into deep water. These topographic zones, which will be described in more detail later, have some similarity to those seen in the Cayman Islands (Logan 1994; Roberts 1994), Belize (Rützler and Macintyre 1982) and Roatan (Fenner 1993).

Throughout the Bahamian archipelago the transformation (diagenesis) of soft sediments into hard bottom or rock is the norm. The marine cementation of sedimentary material is usually the result of subsea cementation of aragonite around sands composed of ooliths or shell fragments. In areas where fresh groundwater joins the sea, a process of precipitation of calcium carbonate around these sand grains results in beach rock. This cementation process is rapid in this dry tropical climate (Rankey and Reeder 2010; Whitaker and Smart 1997). Sediments created by calcified algae found on the banks, especially Halimeda, Penicillus, Udotea, and Rhipocephalus, are cemented together through their root systems. This process is enhanced by the presence of sponges and corals to make for a hard bottom community. “Hard bar” or hard bottom communities are not true accreting coral reefs, but are important throughout the carbonate bank system.

Coral Reef Communities

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. Combinations of these types produce different reef zonation patterns from shallow to deep water. The wide range of hard and soft coral species in TCI reefs is shown in Table 9.2.

Table 9.2 Species list of Cnidaria species recorded from reef communities in the Turks and Caicos Islands, compiled from Sullivan et al. (1994, 1996), Steiner (1999) and School for Field Studies, South Caicos, internal reports (http://www.fieldstudies.org/tci)

Bank Patch Reefs

Bank patch reefs are one of two types of patch reefs found in the Bahamian Archipelago and are common in leeward and lagoon environments (Alevizon et al. 1985; Sullivan et al. 1994). These patch reefs are distributed on the banks some distance from islands, and exposed to wave and wind energy of the open bank. Many bank patch reefs are found within 2 km of a margin, and are common along the exposed southeastern platform margin of Caicos Bank (Fig. 9.4). In addition to distance from any landmass, bank patch reefs differ from near-shore patch reefs in that patches tend to be clustered, rather than isolated circular patches. Massive head corals provide the framework of the bank patch reef and there can be great variability in the contributions of algae, sponges, gorgonians, and hard corals to the patch reef surface. Roughly circular in shape, patch reefs south of Ambergris Cay can be moderate (1,000 m²) to large (+10,000 m²) in size. Vertical relief is as high as 10 m and is due to large coral colonies, including acroporids (Fig. 9.5). Large patch reefs are important fisheries habitats, especially for spiny lobster. It is possible that large deep patch reefs may also provide spawning aggregation sites for coral reef fishes.

Fig. 9.4

A typical deep bank patch reef on sloping platform margin of Caicos bank. Rounded heads of Montastrea annularis at left, large colonies of Agaricia at right, branching gorgonians and coiled sponges in between. Depth about 12 m (Photo by Cindy Lott)

Fig. 9.5

Acropora palmata (large) and A. cervicornis (small) growing on the top of a large bank patch reef south of Ambergris Cays, depth about 6 m (Photo by Sullivan Sealey)

Near-Shore Patch Reefs

Near-shore patch reefs are smaller, but more abundant along the bank or leeward side of islands of the Turks and Caicos Islands, occurring at 1–6 m depths (Chiappone et al. 1996). This patch reef type is distinguished from bank patch reefs primarily by its proximity to shore (<1 km). In addition, near-shore patch reefs tend to be adjacent to seagrass beds and are usually isolated and smaller than the clusters of bank patch reefs found further on the banks. Near-shore patch reefs are typically small, averaging 20–30 m in diameter, and roughly circular in shape, but may be quite variable in size (Chiappone et al. 1996). Near-shore patch reefs are constructed by massive frame-building corals but can exhibit substantial variability in the relative abundance patterns of algae, corals, sponges, and gorgonians (Sullivan and Chiappone 1992). Maximum vertical relief ranges from 1 to 1.5 m and is due to living or dead massive corals that comprise the structure of the patch reef (Fig. 9.6). Near-shore patch reefs are common in lagoonal areas near islands in protected environments with offshore fringing or bank barrier reefs in shallow waters, for example 2–5 km wide off Providenciales (Rankey et al. 2009). These lagoons have limestone floors with a thin veneer of mostly biogenic carbonate sediments, each area of which supports its own distinctive benthic biotic community. Sediment grain sizes vary from fine sands to coarse boulders, with sands the dominant sediment type. Coarse-grained deposits are often transported into the lagoon from the rubble zone of the fringing reef during storms. Sands are often colonized by marine grasses and algae, while patch reefs of various shapes and sizes occur in the lagoon, some being elongate reefal ridges with their long axis oriented normal to the shoreline. In between, relatively barren rippled or bioturbated sands cover large areas of the lagoons and are colonized by algae.

Fig. 9.6

Near-shore patch reef off South Caicos showing (centre) colonies of Montastrea cavernosa (above) and Agaricia sp. (below) with encrusting Millepora at right, yellow sponges, branching gorgonians in background, depth about 6 m (Photo by Cindy Lott)

Channel Reefs

Channel reefs are prevalent in the Bahamian Archipelago, and, especially in the Turks and Caicos Islands, along the northern Caicos Bank between cays. Channels serve as major conduits between deep water and bank water. Essentially four bottom types can occur in channels (sand, seagrass, hard-bottom, or reef) and community composition is dependent upon the length, width, and depth of the channel (Sullivan et al. 1994; Sluka et al. 1996). Channels with coral reefs tend to be wider and deeper, and are dominated by massive coral species, often arranged in finger-like ridges parallel to the channel The sizes of channel reefs can vary substantially (<1 to >3 ha), but many are small. Major factors associated with the lack of substantial reef development in such systems are attributed to turbidity, sediment transport, and extreme fluctuations in water temperatures (Lang et al. 1988). Channel reefs can be important locations for spawning of fisheries target species such as the Queen conch Strombus gigas (Hesse 1979).

Near-Shore Fringing Reefs

Fringing reefs are the dominant platform margin reef type in the region. The presence of a fringing reef near sea level and spur-and-groove structure on the deeper reefs, both of which occur in TCI, comprises a reef complex that modifies the effects of waves, reducing their energy and providing relatively quiet-water conditions in the lee of the reefs, where lagoon and shore communities can develop. Fringing reefs are represented by three structural types: (1) those occurring immediately offshore on an island platform, (2) those that form ridges parallel to shore, and (3) those, both shallow (<5 m) and deeper (>10 m) with spur-and-groove development on the seaward side (Zankel and Schroeder 1972; Sullivan et al. 1994). Fringing reefs are often based on outcrops of the island platform, prevalent across bays offshore off South Caicos and Providenciales. Spur-and-groove or buttress reefs consist of elongate coralline spurs or coral bars oriented perpendicular to shore (Shinn 2011). Few spur-and-groove reefs are reported from the TCI banks that are directly exposed to the Atlantic Ocean (Bunt et al. 1981). Spurs or coralline fingers are greater than 100 m in length in some reefs, with the spur surfaces typically found in 8 m to 16 m depth, or sometimes shallower. Spurs are separated by sand grooves from 13 to 18+  m depth. The deeper spur-and-groove sites extend to the fore reef escarpment, or drop-off zone, at 20+  m depth. At several locations in the archipelago, spur-and-groove topography occurs on reef terraces, ranging from wide, gently sloping surroundings to narrow and steep (Zankel and Schroeder 1972; Bunt et al. 1981; Steiner 1999). The eastern Caicos Bank fringing reefs are characterized by spur-and-groove formations dominated by massive head corals (Sullivan et al. 1996; Chiappone et al. 1996). These spur-and-groove features extend towards the platform margin, and are characteristic of the southeastern margin that is not a precipitous drop-off (Fig. 9.7)

Fig. 9.7

Platform margin bank-barrier reefs along the southern Caicos Banks north of Ambergris Cays, showing spur-and-groove structure (Photo by Sullivan Sealey)

The active fringing reef, easily visible from the air, is the reef crest, the shallowest part of the reef complex. This linear wave-resistant reef, where present, separates the protected lagoonal area from the open ocean and is built along the apex of two surfaces sloping in opposite directions, one shorewards, the other seawards. It is well developed along the shoreline or across bays and lagoons such as the small bay east of Cockburn Harbour, South Caicos (Fig. 9.8). The reef crest lies less than 2 km distant from the shoreline off Northwest Point in Providenciales and comprises a mix of corals such as species of Acropora, Montastrea, Diploria and Porites, as well as the hydrozoan Millepora and a variety of red and green algae (Rankey et al. 2009). At low tide the top of the reef crest is at sea level or slightly emergent and waves break over it. It comprises mainly an Acropora-Millepora thicket, the reef crest zone in the islands spanning the Palythoa-Millepora and Diploria strigosa-Acropora palmata zones described for Caribbean reefs by Geister (2011) and typical of moderate wave energy conditions.

Fig. 9.8

(Upper photo) Oblique aerial photo of small bay looking southwest along southern shore of South Caicos towards Cockburn Harbour, showing waves breaking on reef crest, lagoon with nearshore sands (light) and grass beds (dark) behind reef; Long Cay in background (Photo by Sullivan Sealey). (Lower photo) Google Earth aerial image of the same bay, showing the following zones: A back-reef sands, grass beds and rubble; B reef crest; C platform margin hard bottom; D high relief spur-and-groove; E low relief spur-and-groove; F platform margin deep reefs

Platform Margin Bank-Barrier Reefs

Barrier reefs are found throughout the Bahamian Archipelago, and have historically presented the greatest challenge to exploration by sailing vessels in the past. Although not at far from shore or as extensive as the barrier reefs off Belize and Mexico, the bank barrier reefs occur as a line or “ribbon” along the northern platform margin of the Caicos Bank 3 km or more off shore (Fig. 9.9). Structurally, these reefs exhibit a similar biological community composition to fringing reefs such as in the reef crest or breaker zone. Barrier reefs at the platform margin may also have a spur-and-groove topography offshore (Fig. 9.10). While the distinction from fringing reefs is not always clear, barrier reefs differ from fringing reefs in their greater distance from shore and the presence of an extensive back reef environment separating the shoreline from the reef (e.g. Belize). Barrier reefs occur along the northern and eastern platform margin of the Caicos Bank, especially across embayments. Although the “fringing” reef acts as a protective barrier to inshore waters it is discontinuous and there are occasional gaps (cuts) that allow interchange of waters between the lagoon and the open sea. The dominant coral species on the reef crest, as elsewhere in the northern Caribbean, are Acropora palmata and Millepora complanata, the latter occurring in both bladed and encrusting growth forms. Gorgonians are common as subsidiary forms. A. palmata occurs as large arborescent colonies strong enough to withstand the vigorous surf, the upwardly inclined fronds preferentially oriented towards the open ocean. Like its congener A. cervicornis, this species has suffered a marked decline in recent years in many parts of the Caribbean (Lewis 1984) and the TCI is no exception. However, Gaudian and Medley (2000, p. 590) report that “large healthy stands can still be found at Salt Cay, and the exposed sides of Grand Turk , South Caicos and some parts of the Caicos Bank.” Schelten et al. (2006) also noted that A. palmata populations are still in good condition off the coast of South Caicos. Where it is rare or absent its role is taken over by the hydrozoan M. complanata which forms a hedge of vertically-inclined, upwardly-flaring blades facing the direction of wave advance. Other common forms are species of Diploria, Montastrea and sponges, while pillar-like colonies of the meandrenid coral Dendrogyra cylindrus are sometimes present (Fig. 9.11).

Fig. 9.9

Google Earth aerial view of platform margin bank-barrier reef off Whitby, North Caicos, with arrow showing direction of wave advance under influence of prevailing winds from the east. Waves breaking on reef crest, with back-reef linear ridges of rubble and sand from storm waves

Fig. 9.10

Google Earth aerial view of platform margin bank-barrier reef west off North Creek outlet, Grand Turk, showing back-reef sands and rubble, reef crest with waves breaking, and alternating parallel zones of spur-and-groove development seawards

Fig. 9.11

Platform margin bank barrier reef off western Grand Turk Island with pillar coral Dendrogyra cylindrus, Montastrea cavernosa and sponges, depth about 15 m (Photo by Cindy Lott)

Platform Margin Deep Reefs

Wind and wave energies have predominantly influenced the production of the bank system and island formation. The interface of the archipelago and the ocean energies are, in many ways interrelated and represent a defining characteristic of the island system. The lack of surface water on the small islands contributes to very clear water, and deep light penetration energy, supporting coral growth to over 80 m. Such mesophotic coral habitats are characterized by the presence of light-dependent corals and associated communities at water depths greater than normal along the platform margins of TCI. The dominant communities providing a structural habitat in this depth zone are made up mainly of coral, sponge, and algal species. These deep reefs thus provide a transition area from the shallow bank systems to the open seas of the tropical Western Atlantic.

A sand plain at the base of the shallow spur-and-groove zone is very narrow (less than 500 m) along the windward (east) side of the Caicos Bank and terminates at the edge of the fore-reef escarpment between 15 and 30 m depth.(Chiappone et al. 1996). Typically there is a slight elevation before the edge of the escarpment is reached. This escarpment is a steep and, in some places, near-vertical wall (Fig. 9.12) extending to at least 85 m, the approximate limit of coral growth in the region. Narrow grooves form conduits for sediment transport downslope. The escarpment has fewer coral species than the shallower reefs. Remnants of spur-and-groove structure can still be recognized, the spurs forming enormous overhanging buttresses where many coral colonies, in response to reduced light, adopt a characteristic platy growth form. Examples include Montastrea annularis but its congener M. cavernosa generally retains the columnar growth form seen in shallower water. Large platy colonies of species of Agaricia spread laterally far beyond their narrow base of attachment, eventually becoming unstable and sliding downslope. Although Chiappone et al. (1996) recorded only 16 and 18 coral species, respectively, from 2 sites on eastern Caicos Bank, Steiner (1999) recorded 26 species of corals in this deep zone, the most important of which are species of Montastrea, Agaricia, Siderastrea, Stephanocoenia and Porites. Species of Mycetophyllia, Colpophyllia and Eusmilia are common subsidiary forms. Black corals belonging to Antipathes are present on vertical faces in deeper water (Fig. 9.12), while demosponges occur in a variety of growth forms, mostly whip-like and tubular and include Agelas sp. and Aplysina archeri (Steiner 1999). Enormous barrel sponges belonging to Xestospongia muta are present, as they are throughout the deep reefs of the Caribbean.

Fig 9.12

Deep reef wall off Grand Turk Island, with the sponge Agelas and large branching colonies of the black coral Antipathes at about 30 m depth (Photo by Cindy Lott)

Non-Reefal Hard Bottom Communities

There are four types of non-reefal hard-bottom communities in the region: channels with algal-dominated benthos; channels with sponge/gorgonian-dominated benthos; near-shore hard bottoms and platform margin with algal-dominated benthos. These communities on consolidated carbonate sediments are important habitats for corals, and can be rugose, with ledges, cracks and crevices, but are not actively-building or accreting with massive scleractinian corals.

Channels with Algal-Dominated Benthos

Tidal channels or cuts in the banks are created and maintained by unequal semi-diurnal tides. Channels moving water on and off the platform can be floored by sand, coral reefs or non-reefal hard bottoms. Channels dominated by hard bottoms or consolidated sediments are often algal-dominated. The substratum is typically scoured and very low profile, consisting of exposed and lithified oolite of Pleistocene or Holocene age. Maximum vertical relief is generally less than a meter. Algal-dominated channels are often characterized by rooted Sargassum or other Phaeophyceae such as Turbinaria or Dictyopteris.

Channels with Sponge-Gorgonian Benthos

Channels with hard bottoms can also be sponge-gorgonian dominated. The substrate is typically scoured, and very low profile, with rubble. The consolidated sediments are exposed Pleistocene oolite. Maximum vertical relief is generally less than 1 m.

Near-Shore Hard Bottom Benthos

Several natural processes of cementation, lithification, and levels of crystallization result in a hard underwater surface. Along the rocky shores of the small islands and cays, near-shore hard bottom communities provide an important community, often dominated by tolerant, fast-growing coral species such as Diploria strigosa, D. clivosa, Porites astreoides, Stephanocoenia intersepta and Dichocoenia stokesi. Mixed facies of oolite with skeletal or coral sediments are the dominant base sediments in many areas, with low-relief sponge and coral colonies indicative of the high wave energy occurring in these areas. Near-shore hard bottom communities in the Bahamian archipelago are typically regarded as a recently-submerged extension of island platforms.

Platform Margin with Algal-Dominated Benthos

The platform margin or rims of bank systems in the Bahamian Archipelago consist of a matrix of bare sand, fringing or barrier reefs, and low-relief hard bottom substrates. Low relief hard bottom is the dominant, shallow-water (<20 m) community type found on the platform margin in this region, especially on the exposed sides of banks such as the eastern Caicos banks. The substratum consists of exposed, lithified sand-rock and is not of reefal origin, as in other locations such as the Florida Keys (Wanless and Dravis 1989). Platform margin hard bottoms are the least variable of the hard bottom community types, both reefal and non-reefal, throughout the Bahamian Archipelago. This community type is consistently dominated by algae with occasional patches of sand, and is also referred to as “hard-bar” or windward hard bottom (Sluka et al. 1996). The substrate is very low profile, although occasional ledges and fissures in the substratum surface may occur. Variations in relief are due principally to the presence of isolated coral heads (<0.5 m). This is the primary fisheries habitat on the Caicos Bank (Medley and Ninnes 1999; Tupper and Rudd 2002). Steiner (1999) recorded the algae Dictyota and Lobophora, plus species belonging to 3 genera of gorgonians, and a total of 17 species of corals from off eastern Long Cay at a 9 m-depth station in this zone, the most abundant corals being Porites astreoides, Siderastrea siderea and Dichocoenia stokesi. Similarly the hard bottom surveyed by Sullivan et al. (1994, 1996) and Chiappone et al. (1996) off the eastern Caicos Bank, and particularly South Caicos at 6–10 m depth, lies above the zones of high-and low-relief spur-and-groove and is characterized by the dominance of algae, gorgonians, sponges and 23 species of small encrusting stony corals, although percent coral coverage is low. This relatively high-energy zone may be equivalent to the sparsely-colonized “barren rock pavement” zone described seawards of the fringing reef crest in Cayman Brac and Little Cayman by Logan (1994) and the “shallow forereef “ zone in Roatan by Fenner (1993).

Reef Community Ecology and Diversity

The dominant influence on shallow marine substrates and their communities in the area is the prolific growth of reef-building corals, which, together with calcareous algae and a host of invertebrate species, help establish coral reefs. Coral reefs, consisting of a consortium of corals and calcareous algae, occur at three depth levels. Each coral habitat type displays a zonation in response to light, wave energy and currents. The reef zonation scheme off the east coast of South Caicos, as described by Sullivan et al. (1994), Chiappone et al. (1996) and Steiner (1999) includes bank and lagoonal habitats, reef crest, fore reef and deep reef developments.

Due to very specific habitat requirements (e.g. water quality and temperature), corals are inherently sensitive to environmental variability. Community composition and population size structure are heavily influenced by environmental cues (Hughes and Connell 1987; Pandolfi et al. 1999), and environmental conditions also affect individual colony attributes, such as growth rates, fecundity, and survival (Coles and Fadlallah 1991; Dizon and Yap 2006). While offshore reef tracts are considered to supply “optimal” habitat requirements, corals are found in a wide variety of seemingly highly stressful habitats near to shore and land-based sources of pollution. Corals in the TCI are well established in shallow back-reef and hard-bottom areas, as well as on outcroppings and occasional substrates in seagrass beds, sand plains and artificial structures. Some corals can tolerate temperatures up to 36–40 °C, not unusual on the large shallow bank areas of TCI. A typical mosaic of coral habitat ecotypes is shown off Long Cay in the Admiral Cockburn National Park (Fig. 9.13). The large area of shallow banks with small islands along the margin allows for a diversity of depth, current, wave energy and substrate settings for coral recruitment and growth. Although these coral habitats include many of the same species of coral, the abundance and dominance changes between habitats.

Fig. 9.13

Photo-mosaic illustrating the diversity of reef types in close proximity to Long Cay, Caicos Bank where there are near-shore hard bottoms, bank patch reefs, near-shore patch reefs, channel reefs and bank-barrier reefs to provide slightly different current and abiotic environments for corals and reef-associated fauna (Photos by Sullivan Sealey)

Disturbance has long been recognized as an important factor contributing to community composition (Connell 1978). Hurricanes are known to play important roles in coral reef ecosystems, such as creating new space and restoring evenness to species abundances, as well as indirectly contributing to differential recruitment and population structure (Jackson and Hughes 1985). Hurricane Irene passed through TCI in August 2011, preceded by Hurricane Ike in October of 2008. Hurricanes present a regular disturbance regime, subsequently inducing population changes for some corals, including a higher incidence of colony fission (for example, larger D. clivosa colonies which can be reduced to smaller colonies) and fragmentation (for example Porites porites propagating from fragments). The richness in community diversity and structure of TCI reefs combined with the exceptionally clear water has made this area a text-book example in coral reef and benthic habitat mapping (Mumby and Harborne 1999).

Coral Reef Fish and Fisheries

The Turks and Caicos Islands have historically depended and continue to depend on fisheries as high-value exports (spiny lobster and queen conch, for example) and ecotourism attractions (spear-fishing, flats fishing and deep-water sports fishing). The Division of Fisheries is part of the Ministry of Natural Resources, and is charged with the protection of marine resources to maintain not only biological diversity but also economic sustainability of fisheries through regulation and management of marine fisheries reserves (no-take zones). Fisheries regulations for the major target species: Nassau grouper (Epinephalus striatus), spiny lobster (Panulirus argus) and Queen conch (Strombus gigas) follow Caribbean Fisheries Council recommendations with region-wide size restrictions, gear limits and closed seasons (TCI Fisheries Limits Ordinance 1998). These species are wide-ranging; their management is coordinated with other countries and jurisdictions within the wider Caribbean to maintain sustainable stocks as part of the Caribbean Large Marine Ecosystem initiative.

South Caicos is the center of commercial fishing and fisheries exports. Spiny lobster, conch meat, finfish and even conch pearls are processed and exported from this settlement (Medley and Ninnes 1999). Fisheries officers are closely tied to the Protected Areas Division within the same ministry, and a series of marine fisheries reserves aim to protect key coral reef species from over-exploitation. These marine fisheries reserves serve as important regional research sites dedicated to maintaining healthy reefs and fish populations (Rudd 2001; Rudd and Tupper 2002; Tupper and Rudd 2002; Watson and Munro 2004).

Marine Parks and Protected Areas

Marine parks and protected areas have been implemented as part of the Turks and Caicos Islands resource strategic plan since the late 1980s (Mitchell and Barborak 1991; Zuidema et al. 2011). With the creation of the Turks and Caicos National Trust, along with the Ministry of Natural Resources’ Division of Protected Areas, national parks and preserves are under co-management. The Turks and Caicos National Trust is a non-government organization that has legal authority to manage national parks, and is governed by council. The National Trust has been able to raise funds and bring public attention to coral reef conservation issues, particularly the installation of mooring buoys, vetting zoning in marine parks, and coral reef education.

The focus of marine parks has been two-fold: first, to provide protection for the natural resources of the Turks and Caicos Islands, and second, to provide management of marine areas to benefit tourism, fishing and boating. The newest marine national park, Columbus Landfall Marine National Park, was created in 2009, and covers over 428 ha (1,280 acres) from 1-m above the high water line to 92 m (300 ft) offshore along the platform margin escarpment. Other important parks include uninhabited small cays critical for seabird and turtle-nesting. The distribution of national parks and nature preserves is shown in Fig. 9.14.

Fig. 9.14

Map of Turks and Caicos National Parks, Preserves and Historical Sites, that include coral habitats (Redrawn from Turks and Caicos National Museum)

Many of the National Parks, such as Princess Alexandra National Park on Providenciales, are located near resorts and tourism infrastructure. This national park, along with the new Columbus Landfall Marine Park, cover important coral resources and account for up to 90% of the recreational water sports activities for the country (with Grand Turk and Providenciales being the two main tourism islands).

Coral Reef Assessments and Threats

Regional reef assessments such as “Caribbean Reefs at Risk” (Burke et al. 2011) have long characterized the Turks and Caicos reefs as “low risk” to anthropogenic threats because of the low population density and isolation of the reefs. Assessment studies by researchers have sought to characterize reef geomorphology, obtain fisheries-independent information on target species, and assess countries for protected areas planning. There have been several assessment studies on the reefs of the TCI (Riegl et al. 2003; Hoshino et al. 2003; Schelten et al. 2006; Goreau et al. 2008; Dikou et al. 2009) and the periodic overviews by the Global Coral Reef Monitoring Network on the status of coral reefs in the TCI. However, few studies have been able to address regional impacts from localized threats to coral reef resources. The islands of the wider Caribbean overall face regional threats of global climate change, African dust (Shinn et al. 2000) and eutrophication from land-based sources of nitrogen (Banks et al. 2012), as well as over-fishing (McClenachan 2009).

Regional threats are addressed by regional treaties and agreements, particularly for Small Island Developing States (SIDS). Although a territory of the UK, TCI faces the same challenges as other small island nations in the wider Caribbean. Three threats are particularly critical in the TCI: (1) Population growth and immigration, (2) Coastal development and (3) Capacity to manage reefs and other marine resources. The population of the TCI is one of the fastest growing in the region, with about 22,000 residents, but with ex-patriot workers and second-home owners, the population can exceed 44,000, with most people on Providenciales (67%), followed by Grand Turk (16%). Historically, people have immigrated to the TCI from both Haiti and the Dominican Republic; both countries are only 56 km to the south on the island of Hispaniola. Over the past two decades, the number of refugees and immigrants from this island to the south has contributed significantly to the high population growth rate. A staggering 18.4 million people live on the island of Hispaniola. TCI remains an important trans-shipment country for the movement of people and contraband from the Caribbean to the United States. The largest areas of reef development along the southern extents of the Caicos Bank, the Turks Bank and Mouchoir Bank are the more challenging areas to access and patrol to manage protected areas as well as fishing activity.

Tourism, offshore banking and fishing are the main industries for TCI. Tourism and infrastructure development have altered coastal wetlands and near-shore environments critical to coral reef biota. The challenge to balance economic development against environmental degradation has a direct impact on coral reefs of the TCI. All aspects of development have coastal repercussions on these tropical, dry islands. For example, the construction of reverse osmosis plants for the production of freshwater from seawater, along with marina dredging, has negatively impacted ground water hydrology and near-shore reefs in Grace Bay (Rembert 1999).

The Turks and Caicos National Trust, along with the Division of Protected Areas, Department of Environment and Coastal Resources has embarked on an ambitious agenda to protect the important reefs and coral habitats of the country, relying on the large parks near tourist centers (Fig. 9.14) to generate funding for resource management and especially marine fisheries reserves in more remote areas. The regulatory structure for reef management is in place, but as is often the case, there are not enough resources to implement education, outreach, monitoring, and enforcement across large areas.

The accidental introduction of species of the venomous Indo-Pacific lionfish Pterois spp. (Fig. 9.15) to the Western Atlantic Ocean in 1992 brings into focus the substantial challenges faced by TCI to effectively manage high priority invaders and develop realistic prevention and early detection programmes for other exotics. The invasion of lionfish to TCI waters raises considerable concern due to the uncertainty of its ecological impact and its potential threat to commercial fisheries and human safety. Lionfish have been reported throughout the TCI and are the focus of several research initiatives in South Caicos (Claydon et al. 2008).

Fig. 9.15

Red lionfish Pterois on reefs of South Caicos, depth unknown (Photo by Sullivan Sealey)

There have been several studies to look at the condition of reefs within the TCI in response to pressure from coastal development, diving tourists and fishers. Goreau et al. (2008), using spatially-extensive survey methods for reef surveys in 2006, reached some disturbing conclusions:

• 1. Live coral coverage is surprisingly low at all sites, usually between 10% and 20%, with a large fraction of the dead coral probably resulting from bleaching events in 1987 and 1990, along with mortality from coral diseases. Decreases in coral cover are consistent with reports of regional trends from macro-scale threats to reefs (Bryant 1998).

• 2. Elevated nutrient levels are suspected to have been derived from a combination of deep-water upwelling and land-based sources (exacerbated by increased use of water from reverse osmosis). Eutrophication, along with climate changes, are considered the top threats to coastal systems globally (Moss et al. 2011). For the TCI, chronic eutrophication could gradually change coral-dominated reefs into algae-dominated reefs.

• 3. High turbidity from dredging and cruise-ship propellers at certain localities such as the terminal on Grand Turk may cause increased local coral mortality downcurrent from the source (see also Zuidema et al. 2011). Increased turbidity can also be a component of coastal eutrophication and loss of seagrass meadows.

• 4. Damage to shallow fringing reefs and the regional decline in Acropora palmata and Acropora cervicornis from disease, storm events and elevated sea-surface temperature is posing a threat to TCI lagoons and beaches.

Future management of reefs will require active strategies to protect coral reefs from some of the threats outlined above. In this respect reef restoration projects should be encouraged, notwithstanding the threat of damage from periodic hurricanes (Wells et al. 2010). The Mission Statement of the Department of Environment and Coastal Resources pledges “To ensure sustainable utilization of the natural resources of the Turks and Caicos Islands, protect and promote biodiversity and economic prosperity through a sustainable fishing industry and a protected areas system”. This will remain a formidable challenge into the future to keep this unique reef environment intact.