Chagos Archipelago - Great Chagos Bank West (BITB44)

Setting

BITB44 is the only one of the Three Brothers sites in this group that sits inside the lagoon — a protected leeward submerged bank reef at 29 m, surveyed 23 March 2015 — and it carries the group's highest cover (e.g., Image 4, Image 5, Image 8, Image 13, Image 16).

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General benthic features

Across 25 genera the reef is a two-genus system with a long thin tail: Porites at 18.93% of the benthos, 47% of all coral, and Acropora at 9.36%, the two holding 70% between them (e.g., Image 7, Image 11, Image 28, Image 36, Image 37).

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The strata differ far more in composition than in cover, 39.0% shallow against 42.0% deep, but the deeper one becomes close to a monoculture — Porites rising to 58% of its coral while Acropora nearly halves, genus count falling from 25 to just 9, algal cover halving, and bare substrate tripling to 27.0%.

Coral cover

Formal transects recorded 40.5% coral against 27.9% algae, 49th of 109 Chagos sites for cover and 92nd for algae, with an unusually open 17.7% bare substrate (e.g., Image 9, Image 10, Image 19, Image 38).

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That contrast rests on only two transects, one of which recorded 20% dead coral, the highest reading at either depth here. Image methods read about 12 points lower (CoralNet 28.6%, Coralscapes 28.1%) and should not be averaged. Coral cover: 41%. Live hard coral measured on the in situ benthic transects of the LOF BIOT-1 expedition (Mayfield & Dempsey 2026, Oceans, supplemental S1), against algal cover of 27.9% of the benthos. The transect figure is this site's authoritative cover value; no image-derived product overrides it. Across methods the same reef reads: transects 40.5% · CoralNet points 28.6% · Coralscapes masks 28.1% (36 frames). These products have different sampling footprints and denominators and should not be averaged.

Stressors

Bleaching on the canonical % bleaching (2nd training) column is 5.98%, 69th of 110 dives, mid-range and identical to the first run. Twenty-five of 36 frames were reviewed and agree in kind: two colonies show textbook partial bleaching, a pocilloporid with half its branch mass bone-white against intact brown tissue and a corymbose Acropora with discrete white branch clusters, but no site-wide field (e.g., Image 3, Image 40).

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Broad areas of dead coralline-encrusted pavement carry dense juvenile Acropora recruits, so the reef is visibly recolonizing lost framework (e.g., Image 21, Image 26, Image 27, Image 30).

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No crown-of-thorns, disease, or predation; a lobster aggregation was photographed (e.g., Image 15, Image 29).

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Comparisons with other data

No prior survey data from this site. If you would like to share yours, please email us.