Maldives

The Maldives are a chain of 22 atolls running some 800 km from north to south, the central and largest section of the Chagos-Laccadive Ridge, which traces the path of the Réunion hotspot (Spalding et al. 2001). The atolls rise steeply from the ridge in two parallel rows. The northern end holds Thiladhunmathi and Miladhunmadulu, two names for a single surface-level atoll structure covering some 3,680 km²; the southern end holds Huvadhoo, over 3,200 km², and lies within what the atlas calls the 'Chagos Stricture', a narrow belt of peak coral diversity that links the reef faunas of the eastern and western Indian Ocean. Atoll rims are broad reef flats cut by deep channels, and the 15-55 m lagoons hold patch reefs, knolls, and faros, ring-shaped reefs like miniature atolls that are rare outside the Maldives. At least 209 scleractinian species are recorded nationally, with diversity highest in the south. Coral cover on atoll edges, faros, and lagoon knolls had exceeded 60% to at least 20 m, but in 1998 some areas lost up to 90% of their hermatypic corals. Spalding et al. (2001) estimate about 8,920 km² of reef for the country; Souter et al. (2021) give 6,372 km² for the Maldives ecoregion from a newer map.

This page covers 47 sites in two regions, North and Central, plus Huvadhoo in the far south. North holds eight: seven photographed sites in Baa Atoll and the Raa Atoll site, which has Coral Reef CPR's 2016 bleaching surveys rather than photographs of its own. Central holds 38, five of them atoll-level markers and the rest individual dive sites. Huvadhoo (Gaafu) carries Coral Reef CPR's 2016 transects from the Maamuta house reef, lagoon patch reef, and outer reef. The dived sites come from two periods of fieldwork. In January 2016, research dives in Baa and South Male tagged coral colonies with numbered plates and measured them against rulers along transect lines at Little Sandy Bank, Raaeundi Reef, Veli, Stage, Maafushi, Gaagandufaruhuraa, Kashidhoo Faru, and three further Baa sites; afternoon fun dives on the same trip were made at Big Sand Bank, the Anantara Dhigu, and Kihavah house reefs, Golden Wall, and near Landaa Giraavaru. A later liveaboard covered thilas, channels, walls, and wrecks across North and South Male and Ari, including two night dives dated May 2017.

Coral cover here comes from three kinds of value, at 35 of the 47 sites. Coral Reef CPR's July 2016 point-intercept transects at 7 monitoring reefs (we were part of the CPR team), after the 2016 bleaching, read from 8.0% at Raaeundi Reef to 38% at Gaagandufaruhuraa (Veli by habitat: fore reef 16% · lagoon 5.3%); April 2016, during the bleaching, is the earlier survey on each page. Blind Claude computer-vision point counts of Anderson's photographs give the value at 24 sites, from 2.1% at Fesdhoo wreck to 62% at Four Seasons Landaa Giraavaru, and Claude's photo-based estimates of the January 2016 frames give 37% to 45% at the three Baa research sites. One site keeps an earlier two-method computer-vision index (17% at Anantara Kihavah house reef & Golden Wall). The three kinds are not interchangeable, and the transects describe the reefs after the bleaching. The reefs themselves vary as much as the numbers. Landaa Giraavaru is an unbroken carpet of staghorn thickets and meter-wide table corals stacked in tiers; Kashidhoo Faru is a rolling slope of whorled plate-coral rosettes; Dhega Thila, Hodeli Bodu Giri, and Camel Point carry dense staghorn and table gardens, while Dhigga Thila and Vaadhoo Caves are draped in soft corals and Fish Tank, Fish House, Ghuli Faru, and Moofushi Kandu hold little coral.

What makes this set unusual is that it brackets the 2016 bleaching. The January 2016 frames were made about three months before the El Niño event, a portrait of reefs on the verge. Stress was already visible: a crown-of-thorns starfish below table corals bearing fresh white feeding scars on the Kihavah wall, scattered bone-white branch tips among the tagged colonies at the last Baa monitoring site, and a few white branch tips and one ghost-white staghorn at Veli, where Anderson's January sample sheet records 22 colonies killed by crown-of-thorns starfish on the two research transects; the diver's sheets also describe Raaeundi Reef as ravaged by crown-of-thorns and record one starfish each at Little Sandy Bank and Maafushi. Then the April 2016 resurvey found every recorded colony at Raaeundi Reef bleached, more than nine in ten at Stage, about 95% at Maafushi, four in five at Little Sandy Bank, and nearly half the corals on Veli's channel reef; bleaching was not scored on the sheltered Veli Lagoon reef in April, but it had lost most of its live coral by July (69% to 5.3%). At Lohosfushi Corner, whole terraces of table corals were killed when the reef was devastated by both bleaching and crown-of-thorns starfish (Anderson's account); the 2017 sheet records more than 90% coral mortality at 4-8 m. The May 2017 frames also show algae-covered table skeletons and fresh crown-of-thorns damage at Dhigga Thila, and Pocillopora recruiting across rubble at Back Faru with small colonies recolonizing Miyaru Bay.

Crown-of-thorns starfish are the second recurring problem: the May 2017 removal trip took 952 of them (900 on the 15 reefs in the Coral Reef CPR report, 52 more on 21-26 May). At Dhidhoo Beyru in South Ari Anderson's field sheet records an early-stage outbreak, more than 200 seen, 27 collected, and 5% to 10% of corals eaten; at Hodeli Bodu Giri the crew removed them with a collection stick. Derelict gear is a third: coral-farming tables near the Kuda Giri wreck with most transplanted fragments long dead. In the south, Coral Reef CPR's 2016 transects at Huvadhoo recorded 69% live coral in April and 39% in July, during the 2016 mass bleaching; at Raa in the north the same surveys recorded 46% and 26%.