Chagos Archipelago - Victory Bank (BIVB108)

Setting

BIVB108 is a submerged bank reef at Victory Bank, surveyed 30 April 2015 on a dive to 24.6 m (see Dive record below).

General benthic features

Twenty-nine genera were recorded, with Acropora holding 41% of all coral, Porites 15%, and the archipelago's own Ctenella chagius and the blue octocoral Heliopora in the tail (e.g., Image 1).

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Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Formal transects recorded 47% coral against 43% algae, and the algal budget is turf-led rather than coralline: fleshy turf 14% of benthos against coralline algae at 12%.
• Transect mean 47 ± 4.4% SE (n = 15 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 46% (Mayfield & Dempsey 2026, Oceans, supplemental S1).
• Cover nearly doubles down the profile, from 30% at the shallowest stratum — where Acropora, Pocillopora, and Porites are nearly co-dominant over turf-and-sediment ground — to 54% and 53% deeper, where Acropora takes 42-47% of the coral and turf-plus-sediment falls from 16% to under half a percent.
• 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 43% 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 11% — and the photographs suggest it is conservative, at least five of 15 frames carrying wholly chalk-white tables beside fully pigmented neighbors (e.g., Image 2, Image 3, Image 4).

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No crown-of-thorns was seen in the photographs. Anderson's field notes from this dive record most pocilloporids as bleaching, bleached, or diseased, much of the reef above 20 m bleaching, and bleached colonies being smothered by algae and cyanobacteria (see Dive record below). The Living Oceans Foundation transects here recorded no cyanobacteria and 0.2% 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 morning dive on 30 April 2015 entered the water at 10:13 and lasted 59 minutes, to a maximum depth of 24.6 m (the field sheet); the notes describe murky water and a reef in bad shape, Seriatopora only below 20 m and quite rare, no P. acuta or P. damicornis, P. verrucosa common at all depths, and the first P. eydouxi seen in many dives, an enormous colony. Anderson sampled three Seriatopora colonies: S. hystrix ChSe153 (collected 10:17 at 24.6 m; small, 100% bleached, green fluorescence, partly smothered by algae), Seriatopora sp. ChSe154 (10:27, 20.7 m; potentially healthy, yellow-green fluorescence, intermediate between S. hystrix and S. aculeata), and S. hystrix ChSe155 (10:32, 20.7 m; 100% bleached, being overgrown by cyanobacteria, possibly dead). For a collaborator Anderson also sampled four pocilloporids (species by field call): Pocillopora verrucosa ChJo277 (10:42, 16.0 m; more than 90% bleached; most colonies were bleached) and ChJo278 (10:52, 14.7 m; more than 95% bleached, common at 15 m), Pocillopora eydouxi ChJo279 (10:59, 11.6 m; healthy, the only one seen), and Pocillopora sp. ChJo280 (11:05, 10.5 m; more than 95% bleached, with many bleached colonies nearby). 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

Anderson's field sheet (LOF fellowship 2016 workbook) leaves the reef type and aspect blank, so no aspect is printed; 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.