Turks and Caicos Islands

The Turks and Caicos Islands form the southeastern end of the Bahamas Platform: limestone islands scattered across the small Turks Bank and the far larger Caicos Bank, together some 8,000 km², whose edges fall away sharply into deep ocean water (Wells 1988; Spalding et al. 2001). Geologically they resemble the Bahamas, and with no rivers, runoff from land is very low. Wells (1988) notes that comparatively little was known about the reefs, relying mainly on surveys by Ray and Sprunt in 1971, a 1984 review by Lott and colleagues, and the 1985 Operation Raleigh expedition. Off Providenciales, a barrier reef lies 2.5–3 km offshore between Northwest Point and Leeward-going-through Cut, enclosing many Acropora patch reefs, and the 35 sites surveyed there in 1985 were judged to be in good condition. The reefs around South Caicos, including the wall off Cockburn Harbour, were considered possibly the most productive in the islands because of nutrient-rich upwelling from the Turks Island Passage. Spalding et al. (2001) record true fringing reef along southern Long Cay, the south coast of South Caicos, and the north coasts of Middle and North Caicos, roughly 37 species of coral and upward of 400 of fish, and hard coral cover averaging 18% on the bank edges in 1999. They add that coral diseases probably contributed to widespread losses of Acropora, though sizable stands of A. palmata survived, and estimate the territory's reef area at about 730 km².

Souter et al. (2021) do not report on the Turks and Caicos separately. The closest grouping in their analysis is Bermuda and The Bahamas, a subregion built on the Bahamian marine ecoregion, where mean hard coral cover dropped sharply between 2002 and 2005 without recovering, going from 17.6% in 1999 to 13.3% in 2019, while algal cover climbed after 2011 to reach 64.4% in 2019. For the Caribbean as a whole, the report links coral losses to the 2005 mass bleaching, hurricanes, polluted, and nutrient-enriched coastal water, and overfishing of herbivores such as parrotfishes, and names invasive lionfish, Sargassum influxes since 2011, and stony coral tissue loss disease (SCTLD) as newer threats, with SCTLD reported from the Bahamas by 2021. Closer to home, Spalding et al. (2001) judged that as of about 2000 the islands' reefs showed little sign of human damage, apart from local nutrient discharge on Providenciales and diver impacts at some sites, but saw proposed harbor and tourism projects on East and South Caicos as a significant emerging threat.

The Turks and Caicos unit covers eleven sites dived between 31 July and 5 August 2022 off Northwest Point on Providenciales, off West Caicos, and at French Cay, with maximum depths from 25.3 m at Shark Hotel to 32.3 m at Rock and Roll and Spanish Anchor. Six of the eleven are walls or wall cuts. The Amphitheatre has a bowl undercut into the face at 75-85 ft, Coral Stairway has brain and plating corals climbing the wall in step-like tiers, Shark Hotel has a chimney slot, The Gully is a swim-through with undercut walls, Spanish Anchor drops past 150 ft beside a coral-encrusted 1600s anchor, and Brandywine is a West Caicos wall packed with coral to the crest. Eel Garden is low-relief pavement cut by sand channels, Boat Cove is a field of coral-and-sponge mounds over white sand, and the French Cay sites (Rock and Roll, G Spot) are gorgonian-and-sponge plateaus.

The benthos is dominated by boulder star corals (Orbicella, Montastraea), brain and plating corals, large barrel, elephant-ear, and rope sponges, and dense sea plumes, sea rods, and sea fans. Blind Claude computer-vision point counts of Anderson's photographs put coral cover between 4.6% at G Spot and 20% at Eel Garden, each site the mean of its two dives (Eel Garden includes unedited originals). At most sites these values are upper bounds on living coral, because standing dead skeleton is common: at Coral Stairway whole brain corals kept their shape while dead and overgrown, and at Boat Cove many large colonies had dead, turf-covered centers.

Condition is the main story. Fresh white tissue-loss fronts were photographed at eight of the eleven sites, most heavily at Eel Garden, where some star corals had lost a third to two-thirds of their tissue; at Shark Hotel, where one frame showed ten or more small colonies each carrying its own lesion; and at Rock and Roll. These are described as active tissue loss rather than bleaching, and no syndrome is named from the photographs. Bleaching itself was limited to a few colonies at Eel Garden and single colonies or branches at Thunderdome and Brandywine. Sharks were a constant: Caribbean reef sharks were seen at most sites and nurse sharks packed the reef at G Spot at night, alongside southern stingrays, hawksbill turtles, and horse-eye jacks.