Chagos Archipelago - Salomons Island (BISA104)

Setting

BISA104 is an exposed Salomon forereef whose defining measurement is not its cover but its condition.

General benthic features

Porites leads at 12.61% of the benthos — 35% of all coral recorded — then Acropora 8.49%, Pocillopora 5.59%, Montipora 2.79%, Favia 1.11%, Pavona 0.94%, Goniastrea 0.78%, and Symphyllia 0.61%. Twenty-one further genera sit below 0.5%, among them Stylophora, Cynarina, Isopora, Cantharellus, Mycedium, Plesiastrea, and Hydnophora. Non-coral invertebrates hold 20.4% of the benthos, crustose coralline algae 16.1%, turf 9.8%, and bare substrate 9.8%. Pocillopora is strongest shallow (7.37% 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. One frame centers a broad, table-like colony spanning much of the frame and surrounded by smaller colonies of different forms. 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. 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

Coral cover is a middling 36.2% (64th of 109) against 33.6% algae, but the assemblage is the richest of this batch with 29 non-zero coral genera. Cover is remarkably flat across depth while composition rotates. D2 carries 34.2%, D3 35.1% and D4 39.1% — a range of under five points — but the lead genus changes: Porites dominates the shallows at 19.07% on D2 and 12.45% on D3, while D4 inverts to Acropora at 19.00% with Porites down to 6.30%. Unusually for this archipelago, the deepest band is both the highest in Acropora and the highest in cover, which is the opposite of the pattern at BIPB110 and BIPB61. Assemblage composition. Formal surveys give 36.2% coral, 33.6% algae, and 20.4% non-coral invertebrates, the coral led by Porites in the shallows and Acropora at depth across 29 genera.

Stressors

At 31.5% published image bleaching it ranks 2nd of the 98 Chagos sites with a bleaching figure, behind only BISA84 — and the photographs corroborate that ranking emphatically. Bleaching affects several colony morphologies, which is what makes the 31.5% credible (e.g., Image 3).

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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. No crown-of-thorns starfish (COTS) or other corallivores evident.

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

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