Chagos Archipelago - Victory Bank (BIVB109)

Setting

BIVB109 is a submerged bank reef on Victory Bank, an isolated offshore bank at the north of the archipelago, surveyed 30 April 2015 on a dive to 16.4 m.

General benthic features

Across 26 genera the hydrocoral Millepora leads at 36% of the coral, ahead of Acropora (18%) and Porites (17%). The one depth stratum that holds almost all the Millepora (10 transects; see Coral cover) also carries 24 of the site's 26 genera, including the Chagos endemic Ctenella chagius; the deepest stratum, a single transect, is led by Platygyra, with Porites and Goniastrea next.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Formal transects recorded 48% coral against 37% algae — but here algae means pink pavement, coralline algae holding 15% of the benthos, against just 8.2% fleshy turf (e.g., Image 2).
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• Transect mean 48 ± 5.4% 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 35% (Mayfield & Dempsey 2026, Oceans, supplemental S1).
• The depth profile is strongly structured: cover runs 21%, 59%, 21%, and 38% down the four depth strata (the deepest a single transect), and almost all of the Millepora signal sits in the second stratum, where it reaches 26% of the benthos and 43% of that stratum's coral before vanishing to zero in both deeper ones.
• 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 37% 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 8.7%, and Anderson's field notes from the dive support it: most of the reef was dominated by Millepora, "much of which was bleached," and diseased Pocillopora colonies were common at the site. In the photographs, white branching, knobby, massive, and table colonies stand beside pigmented neighbors (e.g., Image 2, Image 7, Image 15, Image 18).

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Anderson's sampling sheet records four pocilloporid colonies sampled here for a collaborator (species by field call): Pocillopora sp. ChJo281 (16.2 m, healthy, dark pigmentation), ChJo282 (15.5 m, 80% dead, 20% dying), ChJo283 (16.0 m, 50% diseased), and ChJo284 (14.3 m, large, healthy). 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 no cyanobacteria and 0.1% recently dead coral.

Fish and other fauna

Nurse sharks were photographed several times (e.g., Image 3, Image 20), and no crown-of-thorns was seen; Anderson's sheet also notes a sailfish seen from the boat.

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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.

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.