Chagos Archipelago - Blenheim (BIBL87)

Setting

BIBL87 is a submerged fore reef at Blenheim, leeward on Anderson's field sheet, surveyed 23 April 2015 on a dive to 29.9 m.

General benthic features

It holds 37 coral genera and no dominant taxon — Acropora leads at just 19% of the coral present, with Porites, Pocillopora, Pavona, and Montipora close behind (e.g., Image 4, Image 6, Image 10, Image 18, Image 20, Image 21, Image 23, Image 25, Image 30, Image 31).

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Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Formal transects recorded 43% coral cover against 46% algae, with open and sediment-covered ground in places (e.g., Image 8, Image 14, Image 17, Image 22, Image 36, Image 39).
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• Transect mean 43 ± 4.0% SE (n = 16 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 41% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• The three depth transects peak at 53% cover at mid-depth, precisely where the assemblage is most even, between an Acropora-dominated shallow station and a Porites-led deep one under the highest algal cover of the profile.

Stressors

Published bleaching is 9.6%, and the photographs record pale-to-white table colonies at close range over a reef alternating between open crusted pavement and branching-and-table habitat (e.g., Image 1, Image 2, Image 7, Image 13, Image 15, Image 19, Image 27, Image 29, Image 35).

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No crown-of-thorns or disease signs were identified in the 35 stills reviewed. The bleaching percentage is a computer vision figure — CoralNet annotation of the informal survey images, not a diver's field estimate — and human-vs-model agreement is weaker for bleaching (r = 0.40) than for coral cover (r = 0.72). Anderson's sampling sheet records 10 colonies sampled here at 10.3–35.0 m: five Seriatopora hystrix and two S. aculeata by field call; two Pocillopora sp. and one P. verrucosa sampled for a collaborator (field calls); the condition notes run from healthy to 100% bleached, with some partly dead colonies. 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 0.3% 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, one independent station, XL Catlin Seaview Survey at transect 36019, 3.05 km away, read 29% in 2015.

Other notes

Aspect follows Anderson's field sheet (LOF fellowship 2016 workbook: 'forereef', 'leeward'); the expedition's 933-site table classes the station as 'intermediate' (fringing reef). Esri World Imagery (no LOF habitat map covers this station; the LOF Chagos habitat map covers only Peros Banhos) puts the pin on the western side of Blenheim Reef, facing west (about 275°): leeward for the southeast trades that set in during April, as on the sheet, though it would face into the northwest monsoon winds of December to March.