Chagos Archipelago - Peros Banhos (BIPB71)

General benthic features

Assemblage composition from transect data. BIPB71 is an Acropora reef and very little else. Transect counts put Acropora at 46.19% of the benthos — 73.2% of live coral, fifth-highest Acropora in the dataset — with Porites 11.38% (18.0%) a distant second. The remaining nine genera make up under 9% of live coral: Pocillopora 2.00%, Favia 1.63%, Pavona 0.63%, Montipora 0.56%, Platygyra 0.25%, Ctenella 0.19%, Millepora 0.13%, Stylophora 0.06%, Symphyllia 0.06%. Richness of 11 is well below the dataset mean of 23.3; H′ = 0.89, Simpson = 0.43, J′ = 0.37 — the lowest evenness of these eight sites and one of the most lopsided assemblages in the survey. Very high cover on very few genera. Algae and substrate. Total algae is low at 21.56%, and unusually for Chagos plain turf dominates it — 11.13%, 51.6% of all algae — with CCA only 5.00%, erect 2.13%, macroalgae 1.75%, sediment-laden turf 1.50%, cyanobacteria 0.06%. Sediment-turf at 1.50% is a fifth of the dataset mean (7.37%), as a flushed channel setting should read. Bare substrate 7.63%, pavement just 13.44% — lowest of these eight sites, because coral has taken the space — sand 3.33%, rubble 2.89%, PITS 7.75%.

Coral cover

Coral cover averages 62.33% ± 13 SD over a 40–84% range — genuinely high-cover at every transect, none below 40%. Coral cover: 63%. 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 21.6% of the benthos. The transect figure is this site's authoritative cover value; no image-derived product overrides it.

Stressors

The mortality signal is the second story, and it is not small. Dead coral averages 15.67% ± 11.88 SD across the nine transects — the fourth-highest site value in the dataset (mean 4.55%) — and recently dead coral averages 2.0%, with one transect at 12%. Two transects carry 31% and 35% dead coral. A reef with cover this high should not also be among the most dead-coral-laden in the survey, and without imagery there is no telling whether that is storm or predation damage, an Acropora die-back in progress, or the standing skeleton a dense tabular stand always carries. It is the one thing here that the available data cannot resolve.

Comparisons with other data

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

Other notes

Replication and heterogeneity. BIPB71 rests on nine transects across two depth strata, 900 points — all 100-point, so no point-weighting issue, but third-lowest effort of these eight sites. Eight transects sit in D3 and only one in D4, so the site is effectively single-depth and the depth profile is untestable (D3 62.12%, D4 64.0%). Marked `Validation`, one of 37 sites so assigned.