Chagos Archipelago - Victory Bank (BIVB81)

Setting

BIVB81 is a submerged rim reef on Victory Bank, leeward on Anderson's field sheet, surveyed 21 April 2015 on a dive to 31.1 m (see Dive record below).

General benthic features

The coral is packed into just 17 genera, and Acropora alone holds 43% of all coral present.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Formal transects recorded 43% coral against 52% algae, most of it sediment-laden turf (30% of the benthos) and macroalgae (13%), with crustose coralline algae at only 2.7% (e.g., Image 1, Image 2).
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• Transect mean 43 ± 5.3% SE (n = 9 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 52% (Mayfield & Dempsey 2026, Oceans, supplemental S1).
• Cover dips to 34% in the mid-depth stratum, then more than doubles to 78% in the deepest stratum, a single transect, where Acropora accounts for 83% of the coral.
• 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 52% 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 5.1% (CoralNet analysis of the survey images; Mayfield & Dempsey 2026, suppl. S1). The photographs show small stark-white fine-branching colonies beside pigmented table, plating, and massive colonies (e.g., Image 1, Image 2), like the fully bleached Seriatopora colonies that Anderson's notes record as fairly common at 25-30 m, the only depths reached on this late-afternoon dive, and a near-continuous whorled foliose stand (e.g., Image 3, Image 4).

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One of the two Seriatopora colonies sampled was 100% bleached (see Dive record below). The Living Oceans Foundation transects here recorded no cyanobacteria and 0.1% 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. If you would like to share yours, please email us.

Dive record

Anderson's late-afternoon dive on 21 April 2015 entered the water at 16:57 and lasted 27 minutes, to a maximum depth of 31.1 m (the field sheet); the notes describe a very deep submerged bank with beautiful corals at 25-30 m, calm and reasonably clear water but low light so late in the day, and no P. acuta; the shallows could not be found. Anderson sampled two Seriatopora sp. colonies: ChSe100 (collected 17:05 at 31.0 m; large, 100% bleached with a neon-blue hue, fairly common at 25-30 m) and ChSe101 (17:09, 30.0 m; a fluorescent green colony with short, thin, tapered branches, “never before seen,” health unclear). 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 rim reef', 'leeward'); the expedition's 933-site table classes the station as 'protected' (bank reef). Esri World Imagery (no LOF habitat map covers Victory Bank; the LOF Chagos habitat map covers only Peros Banhos) shows only open water over the submerged bank at the pin, so the aspect cannot be checked from imagery.