Chagos Archipelago - Great Chagos Bank North (BINI79)

Setting

BINI79 is a protected submerged bank reef inside the Nelson Island lagoon at 23.4 m, surveyed 20 April 2015 (e.g., Image 7, Image 28).

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General benthic features

Genus richness is in the bottom decile at 12 genera, 102nd of 109, Acropora holding 59% of all coral and the top five genera 97% of it. Cover peaks sharply at the middle station, 43.6% against 26.5% shallow and 24.5% deep, and at the deepest transect Acropora falls to a third of its mid-depth value while Porites nearly catches it and bare substrate reaches 30%.

Coral cover

Formal transects recorded 31.5% coral against 42.7% algae — 73rd of 109 Chagos sites for cover — and the algal budget is soft rather than cemented: fleshy turf takes 19.8% of the benthos, the 5th-highest turf value of the 109 sites, against only 9.4% coralline algae, with 16.3% bare substrate. The image methods recover roughly a third of the transect cover — CoralNet 10.8%, Coralscapes 11.3% against 31.5%. Coral cover: 32%. 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 42.7% 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 31.5% · CoralNet points 10.8% · Coralscapes masks 11.3% (20 frames). These products have different sampling footprints and denominators and should not be averaged.

Stressors

Published bleaching is 5.0%, below median at 70th of 98 on the site table's Mean(%bleaching) column, the first CoralNet training run rather than the canonical % bleaching (2nd training) column — and the photographs do not sit comfortably with it: six frames show stark white or strongly pale colonies beside pigmented neighbors, including two large tables white at the margins with fouled brown centers (e.g., Image 4, Image 9, Image 16, Image 20, Image 22, Image 23).

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Those are logged as ambiguous, since a single still cannot separate partial bleaching from a recently dead skeleton.

Fish and other fauna

A whitetip reef shark, dogtooth tuna, and one cushion star were recorded; no crown-of-thorns or disease (e.g., Image 24, Image 27).

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Comparisons with other data

No independent survey was made at this exact site; the nearest ones are listed in the table below.