Chagos Archipelago - Great Chagos Bank West (BICC36)

Setting

BICC36 is a deep submerged bank reef in Central Chagos, leeward on Anderson's field sheet, surveyed 20 March 2015 on a dive to 30.5 m.

General benthic features

Coralline algae alone takes 15% of the benthos and non-coral invertebrates a further 17%, while fleshy turf is just 7.0% and bare substrate 12%. Only 11 genera were recorded, with Acropora, Porites, Pocillopora, and Montipora holding 88% of the little coral present.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• It recorded 8.6% coral against 63% algae, and that algae splits between sediment-laden turf (34%) and crustose coralline algae (15%), with little fleshy weed (e.g., Image 2, Image 4).
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• Transect mean 8.6 ± 1.9% SE (n = 13 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 5.8% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• The two depth strata run in opposite directions: the shallower carries 9.8% coral, four of its ten genera holding nearly nine-tenths of it, over turf-and-sediment ground, while the deeper collapses to 1.8% as coralline algae quadruples to 42% and Pocillopora replaces Acropora as leading genus — though that stratum rests on only two transects.
• Image-based estimates (CoralNet, DINOv3, CoralSCOP, and Claude) are listed in the method table for comparison only; the transect figure is this site's cover value.

Stressors

Published bleaching is 6.4%, and the 15 photographs show no unambiguous pallor, no disease, no crown-of-thorns. Anderson's sampling sheet logs one colony sampled here as 5% pale or sickly and the other as 15% bleached or pale (see Dive record below). The Living Oceans Foundation transects here recorded no cyanobacteria and 0.1% recently dead coral.

Fish and other fauna

The macrofauna is the set's strength: a spiny lobster, a large octopus, a mantle-extended cowrie, and a glassfish shoal over black coral (e.g., Image 1, Image 3, Image 13).

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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 two pocilloporid colonies on this dive for a collaborator (species are field calls; the sampling sheet): Pocillopora sp. ChJo100 (collected 10:44 at 24.8 m; likely P. verrucosa, 5% pale or sickly, among the few species found at 20 m) and ChJo101 (10:54, 15.9 m; a huge colony, 15% bleached or pale, though much of the healthy part was greenish; bleached part sampled). The dive notes record a strong current and no hard structure above 15 m, and no P. damicornis, P. acuta, or Seriatopora 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).

Other notes

Aspect follows Anderson's field sheet (LOF fellowship 2016 workbook: 'lagoonal bank reef', 'leeward'); the expedition's 933-site table classes the station as 'intermediate' (bank 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.