Chagos Archipelago - Great Chagos Bank North (BINI77)

Setting

BINI77 is a protected, submerged patch reef inside Nelson Island's lagoon, surveyed 20 April 2015 on a dive to 25.2 m.

General benthic features

Across 22 genera, Acropora and Porites share the lead at 30% of all coral each. Acropora and Porites were the most common coral genera on this station's transects (13% of the benthos each), followed by Stylophora (3.8%), Pocillopora (3.7%), Favia (2.4%), and Platygyra (1.3%); bare substrate covered 7.2%, behind crustose coralline algae (17%), the largest single living non-coral group (LOF transects; all algae together 38%).

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Formal transects recorded 42% coral against 38% algae, and the algae is mostly hard encrusting growth rather than sediment: coralline algae takes 17% of the benthos and clean turf 16%, while sediment-laden turf is almost nothing at 1.8% (e.g., Image 3, Image 6).
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• Transect mean 42 ± 2.3% SE (n = 12 transects; Living Oceans Foundation per-transect benthic data); the headline above is this all-transect mean, and the published station value, which weights each depth equally, is 43% (Mayfield & Dempsey 2026, Oceans, supplemental S1).
• The depth profile is the finding: cover climbs gently from 41% to 46% 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.
• Live hard coral measured on the in situ benthic transects of the LOF BIOT-1 expedition (the mean of all of this station's transects), against total algal cover (all algal groups) of 38% of the benthos.
• The transect figure is this site's authoritative cover value; no image-derived product overrides it.
• These products have different sampling footprints and denominators and should not be averaged.

Stressors

Published bleaching is 16%, 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 transect that puts Porites level with Acropora (e.g., Image 2, Image 13).

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No crown-of-thorns was seen, and no disease lesion resolves in the photographs, but Anderson's sheet logs two of the colonies sampled as "bleached/diseased" (possible disease), and all three Seriatopora colonies sampled were more than 90% bleached (see Dive record below). The Living Oceans Foundation transects here recorded no cyanobacteria and 0.1% recently dead coral.

Comparisons with other data

Apart from the Living Oceans Foundation survey shown here, we found no other surveys at this site as of 2026. Within 5 km, three XL Catlin Seaview Survey stations recorded station-year means of 3.4–17% hard coral cover in 2015; the nearest, XL Catlin Seaview Survey at transect 36026, 2.20 km away, read 12% in 2015.

Dive record

Anderson sampled seven colonies on this dive (the sampling sheet; species are field calls): Seriatopora hystrix ChSe93 (collected 08:12 at 24.5 m; small, more than 90% bleached, live tissue still evident, in a patch of Halimeda; all four seriatoporids seen at the site were bleached, dying, or dead), Seriatopora sp. ChSe94 (08:18, 21.5 m; 100% bleached, likely still alive, probably S. hystrix), and ChSe95 (08:26, 22.7 m; 100% bleached, a growth form between S. hystrix and S. aculeata, no live tissue evident, possibly dead); and, for a collaborator, Pocillopora sp. ChJo197 (08:10, 25.1 m; healthy, common at the site), ChJo198 (08:35, 14.5 m; 60% bleached or diseased, bleached part sampled), and ChJo199 (08:45, 10.9 m; severely bleached, 60%, candelabrum morphology, bleached part sampled), and Pocillopora verrucosa ChJo200 (08:53, 11.0 m; 30% bleached or diseased, an unusual morphology, sickly part sampled, live tissue still evident). The dive notes record large plate-like Porites at 15–25 m, numerous dead table Acropora, intense surge at all depths, and no P. acuta at the site. Pocillopora acuta colonies from this archipelago were analyzed in Thomas et al. (2026, Global Ecology and Biogeography 35:e70305, https://doi.org/10.1111/geb.70305).