Chagos Archipelago - Great Chagos Bank West (BICC50)

Setting

BICC50 is a submerged bank reef inside the Central Chagos lagoon (dived to 20.1 m), leeward on Anderson's field sheet, surveyed 25 March 2015 (the photo archive files it as BITB50).

General benthic features

The algal budget is 29% sediment-laden turf and 13% erect algae, while coralline algae is all but absent at 4.1%. Only 14 genera were recorded, and Acropora, Montipora, and Porites hold 82% of the coral between them — though even the leading genus covers only 6.2% of the benthos, so even these leading genera are scarce.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• It recorded 15% coral against 56% algae, with a further 23% bare substrate.
• Transect mean 15 ± 3.6% 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 12% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• The depth structure is inverted: the deeper stratum carries 19% coral against 5.3% shallower, the same genus order at both.

Stressors

Published bleaching is 24% (CoralNet analysis of the survey images; Mayfield & Dempsey 2026, suppl. S1), and Anderson's sampling sheet independently logs one of the colonies sampled here as 40% bleached (see Dive record below). A note on this page's photo-comparison table, not on the published figure: in the computer-vision point labels behind that table, 25 of the 26 points labeled bleached fall in four macro frames of a pair of mantle-extended cowries (the notes: 'mating cowries'), whose white mantles were read as coral (e.g., Image 3, Image 4).

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

Fish and other fauna

Two passing sharks were photographed; no disease or crown-of-thorns was seen (e.g., Image 2).

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Comparisons with other data

Apart from the Living Oceans Foundation survey shown here, we found no other surveys at this site as of 2026. If you would like to share yours, please email us.

Dive record

Anderson sampled four pocilloporid colonies on this dive (the sampling sheet): Pocillopora damicornis CHPd46 (confirmed by RFLP; collected 09:34 at 19.0 m; a large, healthy colony 18 cm across, the only P. damicornis-like coral found at the site), and, for a collaborator (field calls), Pocillopora verrucosa ChJo135 (09:03, 19.1 m; a small, young colony, relatively pale) and ChJo136 (09:09, 19.2 m; 40% bleached, some polyps extended, bleached part sampled), and Pocillopora sp. ChJo137 (09:18, 19.0 m; healthy). The dive notes describe a calm, clear, flat bank with little rugosity and low coral cover, only 5–10 coral species, and giant trevally, a huge nurse shark, and mating cowries. 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).

Other notes

Aspect follows Anderson's field sheet (LOF fellowship 2016 workbook: 'submerged bank', 'leeward'); the expedition's 933-site table classes the station as 'intermediate' (patch reef). Esri World Imagery (no LOF habitat map covers the Great Chagos Bank) shows open water with no visible bottom at the pin, inside the Great Chagos Bank lagoon, so it cannot test the aspect; the sheet's lagoon position stands.