Chagos Archipelago - South Brother (BITB34.5)

General benthic features

What the three frames show. The first frame carries the site: a large corymbose Acropora-type table, golden-olive with pale cream axial tips, on coralline-crusted pavement above open sand, with dense clouds of small blue-green damselfish (Chromis-type) and one banded humbug (Dascyllus-type) in the branches (e.g., Image 1).

1

A grayish fluted structure among the branches is compatible with a tridacnid clam; lower right, dark red-orange fine-branched colonies compatible with a pocilloporid. The second frame is a coralline-crusted bommie with a smooth dark-olive encrusting plate of fine dense corallites (compatible with a Porites- or Montipora-type) and a pale cream knobby-branched colony compatible with a Pocillopora-type, still holding tan pigment low down (e.g., Image 2).

2

The third frame is dominated by a wholly chalk-white blunt-branched digitate colony, again compatible with a Pocillopora-type, beside a pigmented Porites-type knob, CCA crust, and heavy turf (e.g., Image 3).

3

One table coral, one bommie, one white colony — that is the whole record.

Coral cover

Coral cover: 47% — from imagery only, with no transect behind it. This is a ".5" site: informal survey images were annotated in CoralNet, but no formal benthic transect was ever run here. The figure describes the frames that were photographed, not a surveyed reef, and it is not comparable with the transect-derived cover quoted at the numbered sites nearby — it must never be pooled or averaged with them.

Stressors

The pale tips are normal axial growth, not bleaching — 0 bleached points of 30. The white colony is the bleaching signal, and its status is unresolved. All six bleached points fall in the second and third frames; the first has none. The 17.1% is the mean of three per-frame ratios — 0.0%, 30.0%, 21.4% — so two colonies in two photographs produce the entire figure. The third frame's colony reads chalky, granular, and filmed in its interstices: recently dead skeleton is at least as good a reading as live bleaching, and Coralscapes scored that frame 4.2% bleached against 6.0% dead, only 3.9% live. Reclassify it and the site falls to 10.0%; drop either frame and it reads 15.0% or 7.1%. The March discrepancy, stated plainly. 17.1% is the 7th-highest of 57 March sites (March mean 7.5%). But the diver who made these surveys records no bleaching in March or April — only May, and the half-month means agree: 6.1 / 8.2 / 8.4 / 10.0% through March–April against 31.8% in early May. The photographs do not corroborate 17.1% — the frame holding most of the coral is entirely unbleached, and the figure rests on two colonies, one possibly dead. Note too that three of the seven highest March figures are the ".5" half-sites — BIEA24.5 (27.8%), BIDI16.5 (19.7%), BITB34.5. They are not more bleached; they are more thinly sampled. No crown-of-thorns starfish (COTS) or other corallivores evident.

Comparisons with other data

The neighboring full site BITB34 — same island, same day, dived at 13:49 — supplies the context this one cannot: 61.1% transect cover, 31 genera, H′ = 2.206, Simpson 0.797, J′ = 0.642 (Acropora 40.6% of live coral).

Other notes

No transect exists. BITB34.5 is absent from all three benthic sheets — `benthic data by site (n=109)`, `by transect (1556)`, and `by site-depth (336)` — so there are no per-genus columns, no algal cover, no `PB`, no `PITS`, and no basis for genus richness, Shannon H′, Simpson, or Pielou's J′. Read BITB34.5 as a small unsurveyed patch inside that assemblage, never as an independent measurement of it.