Chagos Archipelago - Victory Bank (BIVB109)

Setting

BIVB109 is a protected submerged forereef on Victory Bank, an isolated offshore bank at the north of the archipelago, surveyed 30 April 2015 at 31.2 m; the published reef-type cell is blank, so no class is asserted.

General benthic features

Across 26 genera the top three are near-equal and one is a hydrocoral: Acropora 21% of the coral, Porites 20%, Millepora 19%. That transect also carries 24 of the site's 26 genera, including the Chagos endemic Ctenella chagius; the deepest station hands the lead to Platygyra and Goniastrea.

Coral cover

Formal transects recorded 34.7% coral against 42.0% algae — 66th of 109 Chagos sites for cover — but here algae means pink pavement, coralline algae holding 20.7% of the benthos, 20th-highest of 109, against just 7.3% fleshy turf (e.g., Image 2).

2

The depth profile is among the most structured in the dataset: cover runs 20.5%, 59.22%, 21.2%, 38.0%, and the entire Millepora signal sits on one transect, where it reaches 25.70% of the benthos and 43% of that station's coral before vanishing to zero at both deeper ones. Method agreement is unusually good — Coralscapes 32.7%, CoralNet 24.5% against 34.7% — but the three are still not interchangeable. Coral cover: 35%. Live hard coral measured on the in situ benthic transects of the LOF BIOT-1 expedition (Mayfield & Dempsey 2026, Oceans, supplemental S1), against algal cover of 42% of the benthos. The transect figure is this site's authoritative cover value; no image-derived product overrides it. Across methods the same reef reads: transects 34.7% · CoralNet points 24.5% · Coralscapes masks 32.7% (33 frames). These products have different sampling footprints and denominators and should not be averaged.

Stressors

Published bleaching is 8.7%, 39th of 98 on the site table's Mean(%bleaching) column, the first CoralNet training run rather than the canonical % bleaching (2nd training) column, and it deserves extra skepticism: Millepora is naturally pale cream and a thicket of it reads near-white under blue light, so no bleaching was called from those frames; the mixed frames look normally pigmented.

Fish and other fauna

Three whitetip reef shark encounters, no disease or crown-of-thorns (e.g., Image 3, Image 4).

34

Comparisons with other data

No prior survey data from this site. If you would like to share yours, please email us.