Chagos Archipelago - Peros Banhos (BIPB64)

Setting

BIPB64 is a windward fore reef on the south rim of Peros Banhos, dived to a maximum depth of 29.9 m on 15 April 2015; Anderson's notes describe a fairly steep fore-reef wall with mild current and very high coral cover; the transects, which average every depth, give 33%, with cover falling as algae takes over the deeper strata.

General benthic features

Porites is the leading genus at 10% of the benthos, followed by Acropora, Pocillopora, and Montipora, and coral cover declines with depth as algae takes over the deeper strata. Photographs show a structurally complex reef alternating between dense coral thickets and open sand-and-rubble flats, with sheltering sweetlips, triggerfish, and anemones hosting anemonefish (e.g., Image 1, Image 2, Image 3, Image 5, Image 6, Image 9, Image 10, Image 12, Image 13, Image 14, Image 18, Image 19, Image 25).

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Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• The expedition's transects recorded 33% live coral cover against a higher 41% algal cover, with 9.5% of coral imagery showing signs of bleaching (e.g., Image 8, Image 15, Image 16, Image 20, Image 21, Image 22, Image 24, Image 26, Image 27).
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• Transect mean 33 ± 2.1% 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 31% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• The bleaching percentage is a computer vision figure: CoralNet annotation of the informal survey images, not a diver's field estimate (Mayfield & Dempsey 2026, suppl. S1).

Stressors

Several colonies show clear, colony-scale bleaching consistent with the published figure, including one large table coral photographed almost entirely white (e.g., Image 4, Image 17).

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Anderson's sampling sheet records three pocilloporid colonies sampled here for a collaborator (species by field call): Pocillopora sp. ChJo167 (20.9 m, bleached and diseased, healthy part sampled); Pocillopora verrucosa ChJo168 (14.9 m, 40% bleached) and ChJo169 (10.8 m, healthy). 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). The Living Oceans Foundation transects here recorded 0.2% cyanobacteria and no 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 independent stations recorded station-year means of 20–29% hard coral cover in 2015; the nearest, XL Catlin Seaview Survey at transect 36005, 1.50 km away, read 20% in 2015.

Other notes

Reef type and aspect follow Anderson's field sheet (LOF fellowship 2016 workbook: 'fringing reef', 'windward'); the south rim faces south, into the southeast trades. The LOF habitat map has no reef polygon within 65 m of the pin (nearest 'deep fore reef slope' 125 m); the expedition's 933-site table classes the station as 'intermediate' (fringing reef).