Chagos Archipelago - Salomons Island (BISA103)

Setting

BISA103 is a steep windward fore-reef wall outside Salomon atoll (“forereef” on Anderson's field sheet), surveyed 29 April 2015 on a dive to 29.4 m (see Dive record below).

General benthic features

The assemblage is broad, with 28 non-zero coral genera. Porites leads at 13% of the benthos — 39% of all coral recorded — with the branching component carried by Stylophora at 5.4% and Pocillopora at 3.9%. Pavona follows at 1.9%, Acropora only fifth at 1.2%, then Goniastrea 1.2%, Montipora 1.0%, and Favia, Astreopora, and Gardineroseris 0.8% each. Sixteen further genera fall below 0.5%, including Physogyra, Oulophyllia, Cantharellus, Oxypora, and Hydnophora. Non-coral invertebrates hold 20% of the benthos, crustose coralline algae 16%, turf 16%, and bare substrate 5.2%. Reef architecture is moderate, with colonies set into older consolidated framework and separated by small sand or rubble pockets (e.g., Image 1).

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Broad views show rounded massive colonies, compact branching clusters, low plates, and encrusted surfaces rather than one continuous canopy (e.g., Image 3, Image 4).

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Two frames are useful for the juxtaposition of branching and massive forms around open substrate, and a later run of frames shows repeated changes in colony scale and relief over a short route (e.g., Image 7, Image 11, Image 13, Image 14).

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The result is a heterogeneous habitat with many edges and crevices. The photographed benthos includes purple and red encrusting surfaces, brown algal growth, and small mound-forming colonies, all adding texture and microhabitat diversity — the visible counterpart to a 20% non-coral invertebrate figure. The photographs show massive, compact branching, and plating forms embedded in encrusted framework with small sand and rubble openings, and bleaching common and conspicuous across multiple frames.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• 33%, against 42% algae — but published image bleaching is 24%.
• Transect mean 33 ± 3.5% 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 32% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• Coral cover falls by more than half from the shallowest band to the deepest.
• D2 carries 47% — a genuinely coral-abundant shallow reef, with Porites at 25% and Stylophora at 7.7%, across 24 genera.
• D3 drops to 29% and Porites collapses to 6.6%, leaving Stylophora (5.9%) and Pocillopora (5.3%) nearly level with it.
• D4 falls again to 21%, with Porites at 7.9% and algal cover at 40%.
• Genus richness declines with cover, from 24 to 22 to 19 codes.
• The 13% site-level Porites figure is therefore carried mainly by the shallow stratum (D2, six transects) and does not describe the deeper reef.
• Formal surveys give 33% coral, 42% algae, and 20% non-coral invertebrates, the coral Porites-led with a Stylophora–Pocillopora branching component and Acropora only fifth.

Stressors

Bleaching is visually prominent and matches the high published figure. One frame contains several colonies at different degrees of pallor: one central branching colony has white branch ends and light tissue farther inward, while neighbors range from darkly pigmented to nearly white (e.g., Image 2).

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Another frame shows a large table- or foliose-like colony whose upper surface is coherently white, with intact corallite and plate structure still visible. Additional pale colonies occur in a later run of frames. The recurrence across both wide and close views makes bleaching the most parsimonious reading. Not every pale feature is classified as bleaching. White branch tips can reflect active growth, bright illumination, or normal interspecific color, and some exposed skeleton is already dulled by sediment or overgrowth. The examples cited were chosen because pallor extends broadly across intact tissue and contrasts with nearby pigmented colonies. Small dark points on the large pale table- or foliose-like colony could be attached organisms, sediment, or localized mortality, but they do not justify a disease diagnosis. Four of the five colonies Anderson sampled here were more than 90% bleached or pale (see Dive record below). The Living Oceans Foundation transects here recorded 0.2% cyanobacteria and 0.2% recently dead coral.

Fish and other fauna

Several frames show fish close to the substrate, including small damselfish-like and surgeonfish-like silhouettes, but the sequence is not a fish census.

Comparisons with other data

Sannassy Pilly et al. (2024) surveyed a nearby station (Takamaka), 0.22 km from the pin. Within 5 km, two independent stations recorded station-year means of 9.9–43% hard coral cover between 2006 and 2020; the nearest of these, Lange et al. (2021) at Salomon Atoll, 0.97 km away, read 9.9–43% between 2006 and 2020.

Dive record

Anderson's morning dive on 29 April 2015 entered the water at 08:19 and lasted 52 minutes, to a maximum depth of 29.4 m (the field sheet); Anderson's notes describe a “steep, beautiful forereef wall, very clear, mostly sea fans at 30 m,” with no Seriatopora hystrix or P. acuta at the site and most pocilloporids bleached, diseased, or partly dead: in several random surveys of 20 colonies, about half of the pocilloporids were at least partly bleached, at 15 m and at 10 m alike. Anderson sampled five pocilloporid colonies (Pocillopora sp., the local morphology) for a collaborator: ChJo268 (collected 08:30 at 25.0 m; 100% bleached, partly dead), ChJo269 (08:36, 20.8 m; more than 95% bleached, some pigment in the interior), ChJo270 (08:43, 15.5 m; badly bleached, more than 90% pale), ChJo271 (08:46, 15.2 m; healthy, though only about 10% of the colonies within 5 m were unbleached), and ChJo272 (09:04, 9.3 m; more than 95% bleached, live tissue still evident). 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), and the field sheet gives no aspect, so the aspect printed above comes from the station's GPS position on the southeast side of the atoll (about 19° off the prevailing southeast trade winds, which reads windward); satellite imagery (Esri World Imagery) agrees: the pin lies off the southeast-facing outer reef, which faces into the prevailing southeast trade winds.