Chagos Archipelago - Salomons Island (BISA104)

Setting

BISA104 is a side-on fore reef outside Salomon atoll (from its position on the northeast side of Salomon atoll relative to the prevailing southeast trade winds), surveyed 29 April 2015 on a dive to 30.7 m (see Dive record below); its defining measurement is its condition rather than its cover.

General benthic features

Porites leads at 13% of the benthos — 37% of all coral recorded — then Acropora 6.9%, Pocillopora 5.7%, Montipora 2.9%, Favia 1.2%, Pavona 1.1%, Goniastrea 1.0%, and Stylophora 0.5%. Twenty-one further genera sit below 0.5%, among them Symphyllia, Ctenella, Isopora, Cantharellus, Mycedium, Plesiastrea, and Hydnophora. Non-coral invertebrates hold 20% of the benthos, crustose coralline algae 16%, turf 10%, and bare substrate 9.9%. Pocillopora is strongest shallow (7.4% at D2). Genus richness rises with depth from 18 to 22 to 21 codes. The reef surface is structurally heterogeneous. Two frames show low to moderate relief with coral heads projecting from consolidated framework (e.g., Image 7, Image 8).

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One frame centers a broad, table-like colony spanning much of the frame and surrounded by smaller colonies of different forms (e.g., Image 10).

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Another shows a sediment pocket bordered by branching and massive colonies, while a short run of frames documents a denser outcrop with varied colony sizes (e.g., Image 13, Image 3, Image 4).

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This is not a continuous table field but a mosaic of coral patches, encrusted hard bottom, and small open spaces (e.g., Image 1, Image 4).

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The photographs show a heterogeneous coral-and-framework mosaic — a very large table-like colony, compact branches, massive heads, and lobate forms — with bleaching widespread and visually severe across multiple morphologies.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• 36% against 34% algae, but the assemblage is rich, with 29 non-zero coral genera.
• Transect mean 36 ± 2.6% SE (n = 18 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 36% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• Cover is remarkably flat across depth while composition rotates.
• D2 carries 34%, D3 35%, and D4 39% — a range of under five points — but the lead genus changes: Porites dominates the shallows at 19% on D2 and 12% on D3, while D4 inverts to Acropora at 19% with Porites down to 6.3%.
• The deepest band is both the highest in Acropora and the highest in cover.
• Formal surveys give 36% coral, 34% algae, and 20% non-coral invertebrates, the coral led by Porites in the shallows and Acropora at depth across 29 genera.

Stressors

Published image bleaching is 31%, and the photographs corroborate that figure emphatically. Bleaching affects several colony morphologies, which is what makes the 31% credible (e.g., Image 3). The broad table-like colony is almost entirely white but retains detailed radial branches and surface structure. One frame shows a compact branching colony with coherent white tissue directly beside a brown branching colony, making the contrast especially diagnostic. Two further frames show pale lobate or thick-branched colonies at close range, and smaller white colonies recur in wider scenes. The distribution across growth forms and across both wide and close frames supports a site-wide stress event rather than a few anomalous colonies. The white colonies generally retain intact tissue contours, which favors bleaching over recently denuded skeleton (e.g., Image 2).

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Some carry small dark or reddish spots and local holes, but these do not form a consistent progressive lesion margin, so bleaching is recorded at high confidence while disease is not. Older dead substrate with algal or coralline overgrowth is present in the mosaic and is separated from freshly pale tissue by its darker, irregular, encrusted surface. Of the four colonies Anderson sampled here, the two from 15-20 m were bleached or bleaching, while those at 30.5 m and 10.5 m were healthy (see Dive record below). The Living Oceans Foundation transects here recorded 0.1% cyanobacteria and 0.1% recently dead coral.

Fish and other fauna

Fish occur throughout the sequence, including dark surgeonfish-like silhouettes and smaller reef fishes around the coral patches, but the frames do not support standardized abundance or richness estimates.

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, four independent stations recorded station-year means of 9.9–43% hard coral cover between 2006 and 2020; the nearest, XL Catlin Seaview Survey at transect 36014, 1.93 km away, read 34% in 2015.

Dive record

Anderson's morning dive on 29 April 2015 entered the water at 10:28 and lasted 54 minutes, to a maximum depth of 30.7 m (the field sheet); the notes record a current that grew stronger through the dive, and a mola mola seen by other divers and a turtle. Counting pocilloporids only, Anderson found none bleached at 30 m, 75% bleached at 15 m, and 65% of 40 colonies bleached at 10 m. Anderson sampled four pocilloporid colonies for a collaborator: ChJo273 (Pocillopora sp.; collected 10:37 at 30.5 m; healthy, the local morphology, among the few coral species at that depth), ChJo274 (Pocillopora sp.; 10:43, 20.3 m; bleaching in progress, about 40% of the tissue already bleached; the bleached part was sampled), ChJo275 (P. verrucosa; 10:50, 15.1 m; 100% bleached, live tissue still evident), and ChJo276 (Pocillopora sp.; 11:09, 10.5 m; healthy and darkly pigmented, with purple fluorescence on the branch tips, uncommon nearby). The notes record no Pocillopora damicornis, P. acuta, or Seriatopora at the site. 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).

Other notes

Anderson's field sheet (LOF fellowship 2016 workbook) records 'forereef' and leaves the aspect blank; the expedition's 933-site table classes the station as 'exposed' (fringing reef). No LOF habitat map covers Salomon atoll (the LOF Chagos habitat map covers only Peros Banhos), so satellite imagery (Esri World Imagery) puts the pin off the northeast- to east-northeast-facing outer reef, near the side-on cutoff for the prevailing southeast trade winds. The aspect shown, 'side-on', comes from the station's GPS position on the northeast side of Salomon atoll relative to the prevailing southeast trade winds (about 89° off the upwind direction; the reef-edge reading agrees), which takes precedence over slope facing, lagoon shelter, imagery, and field labels.