Chagos Archipelago - Peros Banhos (BIPB75)

Setting

BIPB75 lies on the windward fore reef slope outside Peros Banhos (deep fore reef slope on the LOF habitat map), surveyed 19 April 2015 on a dive to 31.2 m (see Dive record below).

General benthic features

Across 20 genera, Porites holds 53% of all coral while Acropora manages only 3.3% of the benthos, so the reef's structure is carried by massive mounds rather than tables. Cover almost halves down the profile, from 63% at the shallowest stratum — where Porites alone is 64% of the coral — to 36% and then 33%, with Montipora rising to a quarter of the coral at the deepest stratum.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Formal transects recorded 46% coral against 31% algae, with coralline algae at 5.6% and non-coral invertebrates taking 18% of the benthos.
• Transect mean 46 ± 4.8% SE (n = 10 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 44% (Mayfield & Dempsey 2026, Oceans, supplemental S1).
• 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 31% of the benthos.
• 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 17% (CoralNet analysis of the survey images; Mayfield & Dempsey 2026, suppl. S1). The photographs show two fully white plating colonies beside pigmented neighbors (e.g., Image 5), plus a deep sand-slope frame of gorgonians, black corals, and sponges that explains the invertebrate reading (e.g., Image 1).

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No crown-of-thorns was seen, but disease was: two of the five colonies Anderson sampled here were diseased (see Dive record below). The Living Oceans Foundation transects here recorded no 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, two XL Catlin Seaview Survey stations recorded station-year means of 21–26% hard coral cover in 2015; the nearest, XL Catlin Seaview Survey at transect 36012, 1.88 km away, read 26% in 2015.

Dive record

Anderson's morning dive on 19 April 2015 entered the water at 08:47 and lasted 51 minutes, to a maximum depth of 31.2 m (the field sheet); the notes call it a “fairly boring forereef site,” with rough conditions at the surface and mild surge below. Anderson sampled five pocilloporid colonies on this dive for a collaborator: ChJo189 (likely Pocillopora verrucosa; collected 08:55 at 29.2 m; small and fairly pale, possibly unhealthy; the pale part, 15% of the colony, was sampled), ChJo190 (Pocillopora sp.; 09:02, 24.4 m; healthy, the local morphology, among the few hard corals below 20 m), ChJo191 (likely P. verrucosa; 09:06, 21.0 m; 10% diseased), ChJo192 (likely P. verrucosa; 09:15, 15.2 m; badly diseased, 60% diseased or bleached; a large diseased branch went to Andy for histology), and ChJo193 (Pocillopora sp.; 09:30, 10.9 m; healthy, among the few unbleached, undiseased corals at 10 m). The notes record no Pocillopora 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

Reef type and aspect follow the LOF habitat map: the pin sits on 'deep fore reef slope' on the atoll's east rim, which faces east, windward of the southeast trades. Anderson's field sheet (LOF fellowship 2016 workbook) records 'fringing reef', 'windward'; the expedition's 933-site table classes the station as 'exposed' (fringing reef).