Chagos Archipelago - Peros Banhos (BIPB62)

Setting

BIPB62 is a leeward lagoonal patch reef in the southwest Peros Banhos lagoon, dived to 30.4 m on 14 April 2015 (station CTD-cast midpoint 30.4°C); Anderson's notes describe a calm, coral-covered pinnacle with very high coral cover and diversity.

General benthic features

It is also strikingly clean ground: non-coral invertebrates hold just 1.7% of the benthos and crustose coralline algae 6.8%, with bare substrate at 6.6%, turf 17%, and erect algae 7.3%. Almost everything here is living coral or turf (e.g., Image 7, Image 19, Image 37, Image 39).

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The assemblage is carried by two genera and only sixteen are non-zero. Acropora holds 33% of the benthos and Montipora 10% — together 74% of all coral recorded — with Echinopora third at 7.7% and Favia fourth at 2.2%. Then Lobophyllia 1.2%, Pocillopora 0.8%, Porites at just 0.6%, Ctenella and Halomitra 0.5% each, Fungia 0.4%, and Platygyra 0.3%. Ctenactis, Favites, Cyphastrea, Stylophora, and Symphyllia fill out the tail at 0.3% or less. The depth zonation is a two-genus story. D2 carries 66% coral of which Acropora alone is 62% — 94% of the coral in that stratum (four transects), an effective monoculture. D3 drops to 51% and hands over to Montipora at 25% with Acropora second at 19%. D4 holds 61% and changes genus entirely: Echinopora 23% and Favia 19%, with Acropora down to 3.0%. D5 holds 61% and is a second monoculture — Echinopora at 54%, 89% of the coral on its single transect, with Acropora at 5.0% and Halomitra 2.0%, with algal cover down to 17% and bare substrate up to 22%. Genus richness collapses at both ends, from ten codes at D3 to three at D5. The site-level figures of 33% Acropora and 7.7% Echinopora describe no single stratum: they are the average of a shallow staghorn-and-table reef and a deep Echinopora bank. One frame shows a near-continuous staghorn and corymbose field running to the limit of visibility with a diver above and fusiliers working over it — matching the D2 stratum (62% Acropora) (e.g., Image 5).

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Several frames show the tabular expression of the same zone, large overlapping plates tiled across the slope into blue water, with a big brown massive lobate colony at the margin (e.g., Image 1, Image 13, Image 14, Image 28, Image 33, Image 34, Image 38).

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The most photogenic frame shows classic pedestalled tables, one a vivid yellow-green, standing above corymbose colonies and purple encrusting framework (e.g., Image 11, Image 31, Image 41, Image 43).

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Other frames show the tables mixed with digitate colonies, corymbose thickets, and large cream lobate domes (e.g., Image 6, Image 12, Image 16, Image 35).

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The deeper, non-Acropora community is thinner in the imagery but present (e.g., Image 10, Image 22, Image 25, Image 30).

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One frame holds a large purple-violet foliose colony with strongly radiating septa growing beside pale mint-green plating colonies, a small free-living fungiid, and a brown meandroid head — the foliose whorled form is consistent with Echinopora, the genus that dominates D4 and D5 (e.g., Image 3).

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Another is a close frame of a single large meandroid brain coral dome, dark olive with deep sinuous valleys, sitting on clean sand (e.g., Image 15).

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One frame shows the algal side of the reef: abundant bright green Halimeda and other green algal growth across the foreground between pale plating colonies, digitate corals, and encrusting purple — the visible counterpart to 7.3% erect algae (e.g., Image 9).

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The photographs document the Acropora half in detail — staghorn fields, pedestalled tables, corymbose thickets — plus a foliose colony consistent with Echinopora, meandroid brain corals, massive lobate domes, and abundant green calcareous algae (e.g., Image 2, Image 4, Image 20, Image 24, Image 26, Image 27, Image 32, Image 47).

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Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Transect coral cover is 59%, against only 33% algae (e.g., Image 8, Image 17, Image 18, Image 21, Image 23, Image 29, Image 36, Image 46).
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• Transect mean 59 ± 6.5% SE (n = 10 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 60% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• Formal surveys give 59% coral, 33% algae, and only 1.7% non-coral invertebrates, the coral 69% split between Acropora in the shallows and Echinopora at depth across just 16 genera.

Stressors

Published bleaching is 6.9% (CoralNet analysis of the survey images; Mayfield & Dempsey 2026, suppl. S1), and the photographs show conspicuous bleaching among the tabular Acropora and fine-branching colonies. Stark-white tables stand beside fully pigmented tan staghorn thickets (e.g., Image 26), a white table lies over pigmented tables (e.g., Image 40), a single white plate sits at the edge of foliose colonies (e.g., Image 45), and a top-down frame shows white fine-branching colonies among pigmented neighbors (e.g., Image 42).

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Anderson's notes record that some Acropora tables were bleaching or about to bleach, with some Pocillopora bleaching as well. Of the nine colonies identified in the field as Pocillopora acuta (CHPd62–CHPd70, collected 14:30–15:22 at 9.9–29.8 m), CHPd65 was 90% bleached, CHPd68 80%, CHPd69 40%, and CHPd67 10%; Anderson also sampled three Seriatopora hystrix colonies (ChSe62–ChSe64), two recorded as 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 0.2% cyanobacteria and 0.4% recently dead coral.

Comparisons with other data

Apart from the Living Oceans Foundation survey shown here, we found no other surveys at this site as of 2026. Within 5 km, two independent stations recorded station-year means of 27–44% hard coral cover between 2006 and 2015; the nearest, Sheppard et al. (2008) at Peros Banhos, 3.18 km away, read a mean of 44% in 2006.

Other notes

Reef type and aspect follow the LOF habitat map: the pin lies 25 m from 'lagoonal patch reefs' inside the lagoon; a lagoon pin has no rim facing, and the sheet's 'leeward' agrees. Anderson's field sheet (LOF fellowship 2016 workbook) records 'lagoonal patch reef', 'leeward'; the expedition's 933-site table classes the station as 'protected' (patch reef).