Chagos Archipelago - Speakers Bank (BISP90)

Setting

BISP90 is a protected submerged bank reef inside Speaker's Bank, the northernmost of the Chagos survey areas, surveyed 24 April 2015 at 24.9 m (e.g., Image 2, Image 4).

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General benthic features

Across 27 genera, 40th of 109, Acropora leads at 11.64% of the benthos, 29% of all coral, ahead of Porites 5.77% and Montipora 4.61%, and the Chagos-endemic brain coral Ctenella chagius is present at 0.27%. The depth finding is a clean handover: the shallower stratum carries 47.1% coral and is emphatically Acropora ground at 18.14% of the benthos, 38% of its coral, while the deeper falls to 32.5% and the ordering inverts entirely — Montipora takes the lead, Acropora collapses to 5.13%, and Goniastrea and Echinopora rise roughly nine- and sixty-fold from near-absence, so the site's figures for those two genera describe no depth at this reef.

Coral cover

Formal transects recorded 39.8% coral against 43.4% algae — 53rd of 109 Chagos sites for cover, 40th for algae — with an unusually evenly split algal budget of macroalgae 12.6%, turf 11.4% and coralline algae 10.3% in near-equal thirds. That deeper stratum rests on three transects against thirteen shallow, yet is weighted equally; transect-weighting would give 44.38% rather than 39.79%. Image methods read 16 to 18 points below the transects (CoralNet 23.3%, Coralscapes 22.3%) and should not be averaged with them. Coral cover: 40%. 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 43.4% 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 39.8% · CoralNet points 23.3% · Coralscapes masks 22.3% (8 frames). These products have different sampling footprints and denominators and should not be averaged.

Stressors

Bleaching on the canonical % bleaching (2nd training) column is 2.08%, 96th of 110 dives, the lowest quartile, with both runs agreeing. All eight retained frames were reviewed: a previous reviewer logged high-confidence bleaching in two of them, and those observations stand, but this rebuild rates them lower — much of the coral here is naturally cream-tipped corymbose Acropora, so pale branches are not by themselves diagnostic (e.g., Image 1, Image 3).

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No crown-of-thorns, disease, or predation.

Comparisons with other data

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