Chagos Archipelago - Great Chagos Bank North (BINI77)

Setting

BINI77 is a protected, submerged patch reef inside Nelson Island's lagoon at 21.8 m, surveyed 20 April 2015.

General benthic features

Across 22 genera, Porites leads with 39% of all coral, then Acropora at 20%.

Coral cover

Formal transects recorded 43.0% coral against 36.0% algae — 40th of 109 Chagos sites for cover — and unusually for a lagoonal site the algae is hard encrusting growth rather than sediment: coralline algae takes 18.2% of the benthos and clean turf 11.8%, while sediment-laden turf is almost nothing at 0.9% (e.g., Image 3, Image 6).

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The depth profile is the finding: cover climbs gently from 40.88% to 45.50% while the leading genus changes at every station — Acropora is 41% of the coral at the shallowest transect, no genus dominates at mid-depth, and Porites takes 68% at the deepest, the two crossing over in between. The image methods read 25 points below the transects — CoralNet 17.6%, Coralscapes 18.0%. Coral cover: 43%. 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 36% 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 43% · CoralNet points 17.6% · Coralscapes masks 18% (11 frames). These products have different sampling footprints and denominators and should not be averaged.

Stressors

Published bleaching is 16.1%, ranked 11th 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 support it unambiguously: a single stark-white table alone in one frame, clustered white plates in another, cream-white branching colonies beside pigmented neighbors (e.g., Image 14, Image 8, Image 15).

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Much of the extensive tabular framework appears to be standing dead and coralline-veneered, which would reconcile a photograph full of tables with a Porites-led transect (e.g., Image 2, Image 13).

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No disease or crown-of-thorns was seen.

Comparisons with other data

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