Chagos Archipelago - Salomons Island (BISA105)

Setting

The characteristic architecture is a sequence of coral-capped blocks and pinnacles separated by narrow sediment pockets. Water clarity changes appreciably across the sequence. Suspended material softens contrast in the first several frames, and some surfaces appear muted or gray from distance and backscatter; later images use closer illumination and stronger color balance. No quantitative turbidity value is supported by the photographs and none is reported.

General benthic features

Porites leads at 14.50% of the benthos, followed by Lobophyllia at 10.83% and Goniopora at 8.92%, an unusual pairing that together with Porites accounts for 68% of all coral recorded. Pavona follows at 4.25%, Acropora only fifth at 3.00%, then Favia 1.75%, Goniastrea 1.17%, and Hydnophora 0.83%. A ten-genus tail below 0.5% includes Echinopora, Ctenactis, Physogyra, Astreopora, Turbinaria, Alveopora, Galaxea, Montastrea, Montipora, and Platygyra. Bare substrate holds 13.8% of the benthos, macroalgae 11.2%, non-coral invertebrates 9.2%, turf 7.7%, and crustose coralline algae 7.5%. The depth structure is a clean handover between the three lead genera. D2 carries 55.0% coral and is the Lobophyllia band — 16.50%, with Pavona 9.75% and Goniopora 5.75% — and is also the richest at 19 genera. D3 holds 54.0% and inverts to Goniopora at 21.00% with Porites 13.50% and Lobophyllia 9.50%, on the site's lowest algal cover of 10.0%. D4 falls to 42.0% and becomes a Porites reef outright at 27.00%, with algal cover rising sharply to 47.0% and richness dropping to eight genera. The site-level 14.50% Porites figure is therefore the average of a band where it is absent from the top three and one where it holds better than a quarter of the benthos. Two frames show plates projecting from older framework and massive colonies stacked above one another (e.g., Image 2).

2

Two more frames show convoluted surfaces with deep crevices providing shelter and shaded microhabitat. One frame emphasizes a pinnacle rising into clear blue water, massive heads around the upper relief, and branching colonies along exposed edges (e.g., Image 4).

4

The prominence of massive, lobate, and mound-forming colonies in these frames is the photographic counterpart to a Porites–Lobophyllia–Goniopora assemblage. Non-coral color and texture are conspicuous. Bright magenta, red, and orange encrusting patches occur on vertical faces and shaded recesses, and brown foliose or blade-like growth appears around a pale branching colony in one frame. These are described morphologically because a still photograph cannot securely separate sponge, coralline algae, and other encrusting taxa in every case, but they demonstrate that shaded and exposed microhabitats differ strongly across the outcrop. The photographs document rugged pinnacles, stacked massive and plating colonies, narrow sediment pockets, and colorful encrusted framework under variable visibility, plus localized bleaching in branching colonies.

Coral cover

BISA105 is a high-cover, high-diversity lagoonal patch reef — 50.3% transect coral cover, 23rd of the 109 Chagos sites, carrying 24 non-zero coral genera — and it is emphatically not an Acropora reef. Assemblage composition. Formal surveys give 50.3% coral, 26.6% algae, and 9.2% non-coral invertebrates, the coral led by Porites, Lobophyllia, and Goniopora in a depth-dependent order.

Stressors

Condition calls are therefore based on coherent tissue pallor across intact colonies rather than isolated bright patches. Bleaching is localized but convincing. One frame shows a branching colony tucked beneath a ledge whose tissue is nearly uniformly white, fine branchlets intact, contrasting with surrounding brown macroalgae and pigmented encrusting surfaces. The pinnacle frame shows two bright branching colonies on a pinnacle contrasting sharply with neighboring brown and tan massive corals, and the next frame gives another angle on pale branches (e.g., Image 3).

3

Other pale surfaces were deliberately excluded: strobe reflection brightens smooth massive colonies, and exposed skeletal patches and naturally pale growth tips can mimic bleaching. The published site figure of 5.6% ranks 64th of 98 — comparatively low, and consistent with bleaching that is present in several branching colonies without being a site-wide event. No crown-of-thorns starfish (COTS) or other corallivores evident.

Fish and other fauna

Small planktivorous fishes occur against blue water in the pinnacle frame and darker reef fishes move among the crevices in earlier views; the frames are not standardized for fish abundance and no individual can be assumed unique across adjacent photographs.

Comparisons with other data

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