Chagos Archipelago - Egmont (BIEG07)

General benthic features

The transect genus list is the community record (LOF BIOT-1 survey, the mean of all of this station's transects) and it is dominated by two genera: Acropora 26% and Lobophyllia 14%, which together carry the great majority of the site's coral, then Millepora 2.5%, Favia 1.2%, Euphyllia 0.8%, Goniastrea 0.7%, Montastrea 0.6%, Stylophora 0.4%, Pocillopora 0.3%, Favites 0.2%, Porites 0.1%, Platygyra 0.1%, Cyphastrea 0.1%, Leptoseris 0.1%, Fungia 0.1%, and Montipora and Pavona at <0.1% each — 17 genera. The substrate and algal categories run turf 19%, sediment-laden turf 17%, bare substrate 9.4%, crustose coralline algae 5.9%, non-coral invertebrates 0.6%, macroalgae 0.6%, and cyanobacteria 0.4%. Seven of the eight are within about a meter of the substrate and only the frame in Image 6 pulls back far enough to show the reef and a water column; the frames are sharp, evenly strobe-lit and naturally colored, with Image 6 the only hazy one.

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This set cannot characterize habitat, relief or zonation at BIEG07, and nothing below should be read as though it could. What the close frames show well is small-scale diversity and the state of the pavement. The substrate in Image 1 and Image 4 is largely dead: crimson and pink crustose coralline algae over gray eroded rock, olive-green algal turf and filamentous growth, black boring holes, loose white Acropora branch fragments and orange-pink encrusting sponges, with live coral reduced to a few small tan colonies and pale Acropora branchlets in the gaps. Image 4 sets a brown knobby colony beside a pale gray-green eroded mass riddled with dark cavities and carrying salmon-pink stubs and encrustation, with a brown fleshy lobed colony at the right — old framework and living tissue side by side, though the pink material cannot be resolved as coral, sponge, or coralline from the image.

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Image 5 is a diverse macro frame: honeycomb- and cerioid-corallite colonies compatible with Favites or Goniastrea, a verrucose brown colony compatible with Pocillopora, tan corymbose and digitate Acropora branchlets, a gray-white convoluted leathery octocoral, a small green encrusting colony, purple and mauve encrusting sheets, pink CCA, and a cluster of long extended polyps — six or seven taxa inside one field of view.

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Image 6 is the one frame that shows the reef, and it is the standout image at the site: an enormous massive boulder filling the frame, healthy and fully pigmented tan-brown, with further coral heads and a hazy blue water column behind it. It is not Porites: the surface carries large meandroid and cerioid corallites with distinct walls and sinuous valleys at centimeter scale, which makes it a merulinid brain coral, compatible with Platygyra, Favites, or Goniastrea. Porites corallites are minute and would give a smooth, finely pitted surface at this magnification.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• 48%, from the Khaled bin Sultan Living Oceans Foundation's BIOT-1 in situ transect survey (the mean of all of this station's transects); the photographs illustrate the site.
• Transect mean 48 ± 5.2% SE (n = 13 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 48% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• Against it the transects put algal cover at 42% of the benthos.
• Anderson's published percentage bleached for this site is 18% (CoralNet analysis of informal survey images; Mayfield & Dempsey 2026, Oceans).
• Image-based estimates in the method table are listed for comparison only; the transect figure is this site's cover value.
• The eight habitat frames were shot almost entirely as close-in macro rather than wide reef scenes.
• The transects record Porites at only 0.1% of the benthos here.

Stressors

Survey conditions on 11 Mar 2015 at 6.66732°S, 71.36813°E: station CTD temperature 30.0°C and salinity 34.1. Image 12 shows a branching colony with algal-fuzzed dead patches interleaved with live tissue.

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Whitening is visible in this set and is worth recording frame by frame. Image 3 is unambiguous: a bone-white to cream branching Acropora colony, its skeleton bare enough in places to be taking on a greenish algal film, sitting among fully pigmented brown and tan lobed massives that show no whitening at all — the contrast inside the frame is the point. Image 2 is a cream-yellow verrucose branching colony compatible with Pocillopora on turf- and coralline-covered rubble; its yellow is natural color, not paling (Anderson's sampling sheet records the small yellow colonies here as healthy). Image 7 is a second branching colony of the same kind, brown over its upper branches and pale cream-tan across its lower and left portions — partial paling rather than whole-colony whitening.

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Whitened branch ends also appear at the right edge and lower right of Image 5, though at that range they cannot be separated from dead branches crusted with coralline. These are descriptions of what is visible in individual frames. No bleaching percentage is estimated from them: eight opportunistically composed macro frames are not a sample of a site's bleached fraction; Anderson's published per-site percentage bleached for BIEG07 is 18%. The extensive dead pavement in Image 1 and Image 4 is logged as mortality of unresolved age and cause; this is a macro set with no wide context, so it cannot be scaled to the site. No disease lesion or predation scar resolves with confidence in any of the eight frames. Anderson's sampling sheet records the nine colonies sampled here as healthy to 20% dead (see Dive record below). The Living Oceans Foundation transects here recorded 0.4% cyanobacteria and 0.1% 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 11–28% hard coral cover in 2015; the nearest, XL Catlin Seaview Survey at transect 36029, 1.94 km away, read 28% in 2015.

Dive record

Anderson sampled nine colonies on this dive (the sampling sheet; species of the CHPd colonies confirmed by RFLP): Pocillopora acuta CHPd5 (collected 14:55 at 10.0 m; small, pale lemon-yellow, polyps extended), CHPd6 (15:04, 10.3 m; small and healthy, living in isolation in sand), CHPd7 (15:09, 9.8 m; strange-looking, dark pigmentation, bulbous branches; the field call was P. damicornis), CHPd8 (15:15, 10.3 m; large and healthy, dark pigmentation), and CHPd11 (15:40, 10.3 m; sickly, 20% dead, dying part sampled); Pocillopora damicornis CHPd9 (15:22, 10.0 m; small and yellow, next to a P. acuta colony), CHPd10 (15:32, 10.0 m; yellow-brown and healthy), and CHPd12 (15:48, 5.8 m; small and healthy, next to P. acuta); and, for a collaborator, Pocillopora verrucosa ChJo20 (field call; 15:38, 10.2 m; pale, though likely healthy, uncommon at the site). The dive notes describe a murky lagoonal patch reef. 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

No depth-stratified (D1–D4) breakdown is available for this site. No quadrat, transect line, or scale object appears anywhere in the set; Anderson's sampling photographs of the nine colonies collected here (each with forceps beside the colony) are on file but are not in this gallery; Image 12 shows an unsampled branching colony photographed between the CHPd9 and CHPd10 collections. No scale object is in frame beside the boulder (e.g., Image 6), so its size is not measured here.