Chagos Archipelago - Great Chagos Bank West (BICC51)

Setting

BICC51 is a submerged bank reef inside the Central Chagos lagoon (dived to 29.2 m), leeward on Anderson's field sheet, surveyed 25 March 2015.

General benthic features

Its defining number is not its coral but its algae: 70% algal cover against 17% coral (e.g., Image 1).

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About half that algal budget is sediment-laden turf at 35% of the benthos, with coralline algae at 15%, while clean fleshy turf is just 3.7% and bare substrate 7.5% (e.g., Image 2).

2

Among the 18 genera, Pocillopora holds 27% of the coral, Porites 19%, Acropora 18%, and Stylophora 10%.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Cover peaks at mid-depth, 13% to 20% and back to 13%; Pocillopora ties with Acropora at the shallowest depth and leads at the middle depth, and Porites leads at the deepest, while algal cover never drops below 68% at any depth.
• Transect mean 17 ± 2.2% 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 15% (Mayfield & Dempsey 2026, Oceans, supplemental S1).
• Image-based estimates (CoralNet, Claude, DINOv3, and CoralSCOP on 17 photographs) are listed in the method table for comparison only; the transect figure is this site's cover value.
• Coral cover: 17%.
• 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 70% of the benthos.
• The transect figure is this site's authoritative cover value; no image-derived product overrides it.

Stressors

Published bleaching is 4.5%, and the 19 photographs show no unambiguous pallor, no disease, predation, or crown-of-thorns. Anderson's sampling sheet logs one of the two colonies sampled here as 5% bleached (see Dive record below). The Living Oceans Foundation transects here recorded 0.1% cyanobacteria and no recently dead coral.

Fish and other fauna

A whitetip reef shark rests under a plating colony across three frames, and the schooling fish traffic is markedly out of proportion to the coral (e.g., Image 3, Image 4).

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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. ChJo138 (collected 11:10 at 20.8 m; a large, healthy colony, polyps extended, among the few common corals at the site) and ChJo139 (11:18, 14.6 m; 5% bleached, an unusual growth form Anderson could not assign to a species, bleached part sampled). The dive notes record a slope from 13 to 30 m, some unusual Seriatopora-like Stylophora colonies at 25 m, and no P. damicornis, P. acuta, or Seriatopora hystrix 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: '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.