Chagos Archipelago - Three Brothers lagoon (BITB34.5)

General benthic features

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

1

Lower right are dark red-orange fine-branched colonies. The second frame is a coralline-crusted bommie with a smooth dark-olive encrusting plate of fine dense corallites 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 knob, CCA crust, and heavy turf (e.g., Image 3).

3

Coral cover

• This is a ".5" site: informal survey images were annotated in CoralNet, but no formal benthic transect was ever run here.

Stressors

Published bleaching for this informal dive is 17% (Mayfield & Dempsey 2026, Oceans, suppl. S1; CoralNet analysis of 3 photographs). The pale tips of the table coral in Image 1 are growth margins. The wholly white branching colony in Image 3 is either bleached or recently dead; the photograph does not settle which. Anderson's field sheet records all nine colonies sampled on this dive as unbleached, one of them more than 30% dead (see Dive record below). No crown-of-thorns starfish (COTS) or other corallivores were evident.

Comparisons with other data

Spalding et al. (2025) surveyed a nearby station (Great Chagos Bank - Middle Brother, lagoon) in 2024, 0.18 km from the pin. Within 5 km, two independent stations recorded station-year means of 21–41% hard coral cover between 2006 and 2015; the nearest of these, XL Catlin Seaview Survey at transect 36004, 1.08 km away, read 21% in 2015.

Dive record

Anderson's afternoon dive on 19 March 2015 entered the water at 15:48 and lasted 60 minutes, to a maximum depth of 10.2 m (the field sheet); the notes describe a murky, calm lagoon dive with low visibility, isolated bommies in the sand at 10 m, and a large bommie rising to about 1 m below the surface, mostly soft corals with some P. acuta; they also note a sickly turtle. Anderson sampled eight Pocillopora acuta colonies (confirmed by RFLP), CHPd26-33, collected 15:56-16:45 at 4.6-9.9 m: all were recorded as healthy or likely healthy and unbleached, with yellow-cream or dark pigmentation, except CHPd32 (5.2 m; more than 30% dead), and dead P. acuta lay near CHPd26. Anderson also sampled one Seriatopora sp., ChSe16 (15:52, 9.8 m; a very strange-looking colony with tiny, brittle branches, possibly S. hystrix, the only one found at the site; unbleached). 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 transect exists. No benthic transect data are available for BITB34.5, so there is no per-genus breakdown, no algal cover, and no basis for genus richness or diversity indices.