Chagos Archipelago - Great Chagos Bank North (BINI79)

Setting

BINI79 is a protected submerged bank reef inside the Nelson Island lagoon, surveyed 20 April 2015 on a dive to 30.9 m (e.g., Image 7, Image 28).

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General benthic features

Genus richness is 12 genera, with Acropora holding 63% of all coral and the top five genera 97% of it. Cover peaks sharply at the middle station, 44% against 27% shallow and 25% 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%. Acropora was the most common coral genus on this station's transects (21% of the benthos), followed by Pocillopora (4.4%), Porites (3.8%), Favia (1.8%), Stylophora (1.6%), and Galaxea (0.5%).

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Formal transects recorded 34% coral against 42% algae, and the algal budget is soft rather than cemented: fleshy turf takes 16% of the benthos, against only 10% coralline algae, with 14% bare substrate.
• Transect mean 34 ± 3.7% SE (n = 11 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 32% (Mayfield & Dempsey 2026, Oceans, supplemental S1).
• 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 42% of the benthos.
• The transect figure is this site's authoritative cover value; no image-derived product overrides it.

Stressors

What the data say. Published bleaching is 5.0% (CoralNet analysis of the survey images; Mayfield & Dempsey 2026, suppl. S1); no colonies were sampled here (Anderson's sampling sheet: no Seriatopora, P. acuta, or P. damicornis present).

What Anderson saw. The photographs show stark-white or strongly pale colonies beside pigmented neighbors in five frames (e.g., Image 9, Image 16, Image 20, Image 22, Image 23), including two large tables white at the margins with fouled brown centers; the table in Image 9 is white across its whole surface with its polyp texture intact, so it is bleached rather than dead.

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The Living Oceans Foundation transects here recorded no cyanobacteria and 0.1% recently dead coral.

Fish and other fauna

A whitetip reef shark, dogtooth tuna, and one cushion star were recorded; no crown-of-thorns or disease appears in the photographs (e.g., Image 24, Image 27), although Anderson's field sheet notes “mostly dead coral, COTS outbreak likely, low diversity/cover at 12 m.”

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Comparisons with other data

The XL Catlin Seaview Survey covered a nearby station (transect 36026) in 2015, 0.41 km from the pin; we could not confirm that it is the same reef. Within 5 km, four 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, 0.41 km away, read 12% in 2015.