Chagos Archipelago - Great Chagos Bank West (BITB45)

Setting

BITB45 is a protected submerged bank reef inside the Three Brothers lagoon at 26.4 m, surveyed 23 March 2015.

General benthic features

What replaces algae is open ground: 22.5% bare substrate and 10.7% turf-on-sediment, so the reef reads as coral thickets and plate stands set on white carbonate sand (e.g., Image 1, Image 2, Image 8, Image 12, Image 15, Image 16).

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Across 23 genera, 64th of 109 and far below the 33 to 34 of neighboring sites, Acropora leads at 21.3% of the benthos and Porites at 12.2%, four genera holding 91% of the coral and evenness at just 0.50 (e.g., Image 5, Image 6, Image 9).

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Coral cover

Formal transects recorded 45.6% coral against just 24.7% algae — 35th of 109 Chagos sites for cover but 99th for algae, the bottom decile — and fleshy turf is only 3.35% of the benthos, 103rd of 109 and among the lowest recorded anywhere in the dataset. The profile runs opposite to most Chagos reefs — Acropora climbing from 15.65% of the benthos shallow to 26.93% deep, 57% of that stratum's coral, while algae halves and bare substrate nearly triples to 32.9% — but it is descriptive only: the deep stratum rests on three transects reading 69%, 36%, and 36.2% and yet supplies half the headline number. Method agreement is the tightest of this group (CoralNet 35.6%, Coralscapes 35.9%), but the three must still not be averaged. Coral cover: 46%. 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 24.7% 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 45.6% · CoralNet points 35.6% · Coralscapes masks 35.9% (13 frames). These products have different sampling footprints and denominators and should not be averaged.

Stressors

Bleaching on the canonical % bleaching (2nd training) column is 7.44%, 56th of 110 dives. All 13 frames were reviewed and show pallor without a demonstrated event: pale mottling and white patches on one large table, unresolved from a single still, plus genuine old partial mortality on another (e.g., Image 3).

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Two of the seven bleached point labels behind the site figure fall inside a nudibranch macro that is not habitat imagery at all (e.g., Image 4, Image 11).

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No crown-of-thorns, disease front, or predation.

Comparisons with other data

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