Chagos Archipelago - Great Chagos Bank West (BIEA52)

Setting

BIEA52 is a protected submerged bank reef inside the lagoon at 20.0 m, surveyed 25 March 2015 and filed to Eagle Island — a label this rebuild disputes, since the site sits east of every Eagle Island station and inside the Three Brothers longitude range, was dived a week after Eagle Island work ended, and maps to the Three Brothers CRD page (e.g., Image 2).

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General benthic features

The striking figure is neither: non-coral invertebrates hold 28.5% of the benthos, more than the entire algal budget, unresolved to taxon. Across 25 genera no taxon exceeds 37% of the coral — Porites 12.38% of the benthos, Acropora 5.85%, Pocillopora 3.98% — an unusually balanced mix (e.g., Image 1, Image 4).

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The profile runs from an invertebrate-dominated shallow band at 13.7% coral and 55.3% invertebrates, through two coral-abundant mid-depth bands at 46.2% and 42.7% carrying 17 and 24 genera, to a single deep transect at 34.0% where Acropora drops out and Pachyseris takes 18% of the coral. A third shows a dead table colonized by a dozen live Acropora recruits.

Coral cover

Formal transects recorded 34.1% coral against 24.1% algae, 67th of 109 Chagos sites for cover and 102nd for algae, among the eight least algae-dominated reefs in the archipelago, with fleshy turf at just 3.0%, 105th of 109. The site has no multi-method row, so the transect figure is its only verified cover number. Coral cover: 34%. 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 24.1% of the benthos. The transect figure is this site's authoritative cover value; no image-derived product overrides it.

Stressors

Bleaching on the canonical % bleaching (2nd training) column is 0.00%, 109th of 110 dives and the lowest of any site with a figure, both runs agreeing — yet one of the 26 frames shows a small intact bone-white colony among pigmented neighbors, so the reef should not be called unbleached. Another frame shows a crown-of-thorns starfish beside a stainless-steel bone-cutting forceps laid on the substrate, a deliberate removal rather than a chance encounter; one individual, no aggregation (e.g., Image 3).

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Comparisons with other data

No independent survey was made at this exact site; the nearest ones are listed in the table below.