Chagos Archipelago - Peros Banhos (BIPB60)

Setting

BIPB60 is a windward fore reef slope on the west rim of Peros Banhos, dived to 30.6 m on 14 April 2015 (station CTD reading 30.0°C), with 42% coral cover and 24 coral genera (LOF transects, 2015).

General benthic features

It is emphatically a Porites reef. Porites alone holds 25% of the benthos — 60% of all coral recorded — with Acropora a distant second at 6.5%, then Pocillopora 3.3% and Montipora 3.0%, and a twenty-genus tail below 0.7%: Pavona, Goniastrea, Astreopora, Leptastrea, Heliopora, Montastrea, Favia, Millepora, Stylophora, Goniopora, Favites, Galaxea, Gardineroseris, Cyphastrea, Turbinaria, Platygyra, Leptoseris, Fungia, Coscinaraea, and Cantharellus. Crustose coralline algae hold 18% of the benthos, turf 14%, bare substrate 10%, non-coral invertebrates 8.2%, erect algae 3.5%, and macroalgae 1.2% (e.g., Image 26, Image 44).

2644

The depth structure is a clean genus handover. The compositional shift across that peak is the real story: above 8 m, Acropora leads at 19% of the benthos with Porites second at 13%. From 8 m down the order inverts and never recovers — Porites takes 33% at 8–12 m against Acropora's 6.5%, then 26% versus 4.5% at 12–18 m, and 20% versus 3.6% at 18–25 m. The site-level figure of 25% Porites is therefore not a uniform value but the average of a reef that is Acropora-fronted in the shallows and Porites-built below them. Algal cover runs inversely, highest in the shallows (48%) and lowest at depth (29%). Two wide frames taken into the surface light show a school of large unicornfish or surgeonfish over the reef, with gorgonian sea fans and thin whip or wire corals standing off the substrate, neither of which appears in the transect genus list (e.g., Image 1, Image 25).

125

Formal surveys give 42% coral, 39% algae, and 8.2% non-coral invertebrates, the coral dominated by Porites below 8 m and Acropora above it. Surgeonfish schools work the reef (e.g., Image 43, Image 45), and a phyllidiid nudibranch was on the coralline pavement (e.g., Image 2).

43452

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Coral cover peaks in the 8–12 m band at 49%, then declines steadily — 39% at 12–18 m, 36% at 18–25 m — while the shallowest band holds 44%.
• Transect mean 42 ± 2.2% SE (n = 19 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 42% (Mayfield & Dempsey 2026, Oceans, suppl. S1).

Stressors

Published bleaching is 12% (CoralNet analysis of the survey images; Mayfield & Dempsey 2026, suppl. S1), and bleached colonies show in several frames (e.g., Image 7, Image 11, Image 27, Image 36, Image 40).

711273640

Anderson's sampling sheet records three pocilloporid colonies sampled here for a collaborator (species by field call): possible Pocillopora elegans ChJo159 (20.8 m, healthy, green fluorescent hue); Pocillopora sp. ChJo160 (15.0 m, healthy) and ChJo161 (10.5 m, 50% diseased). 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 0.1% cyanobacteria and 0.1% recently dead coral.

Fish and other fauna

Nurse sharks swim over the reef (e.g., Image 13, Image 41).

1341

A macro sequence shows a single phyllidiid nudibranch — black ground, pale blue-white ridges, yellow-orange tipped tubercles, photographed from four angles on coralline-crusted pavement (e.g., Image 2, Image 3, Image 4, Image 8).

348

Genus and species are not resolvable from these images alone.

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, two independent stations recorded station-year means of 27–44% hard coral cover between 2006 and 2015; the nearest, Sheppard et al. (2008) at Peros Banhos, 2.60 km away, read a mean of 44% in 2006.

Other notes

Reef type and aspect follow the LOF habitat map: the pin lies 37 m from 'deep fore reef slope' on the atoll's west rim (fore reef slope). Anderson's field sheet (LOF fellowship 2016 workbook) records 'fringing reef', 'windward'; the expedition's 933-site table classes the station as 'intermediate' (fringing reef). The rim here faces west to west-northwest: windward of the northwest monsoon (December–March), leeward of the April–November southeast trades; the printed 'windward' is Anderson's sheet label.