Chagos Archipelago - Great Chagos Bank West (BITB48)

Setting

BITB48 is an intermediate-exposure submerged lagoonal patch reef on the inner side of Three Brothers, surveyed 24 March 2015; no CTD depth, temperature, or salinity value was published, so the site is placed only by depth strata.

General benthic features

Across 22 genera, Acropora leads at 11% of the benthos, 32% of the live coral, with Porites at 9.8%, the two holding about three-fifths of the coral between them. The depth contrast is compositional rather than quantitative: cover barely moves, 34% to 30%, but the reef hands over from a shallow branching Acropora and Pocillopora patch reef on sediment-laden turf to a deeper massive-Porites and faviid ground over 27% bare rock, with Porites nearly doubling to 16% while Pocillopora and Leptastrea drop out to exactly zero. The algal budget is notable for sediment-laden turf at 15%, slightly ahead of the coralline algae at 14%.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Fourteen formal transects recorded 34% coral against 38% algae, with 14% bare substrate and 14% non-coral invertebrates, and individual transects spanning 12% to 62%, so the tidy site figure averages very unequal ground.
• The transect figure is its only cover number.
• Live hard coral measured on the in situ benthic transects of the LOF BIOT-1 expedition (the mean of all of this station's transects), against total algal cover (all algal groups) of 38% of the benthos.
• The transect figure is this site's authoritative cover value; no image-derived product overrides it.
• Transect mean 34 ± 3.8% SE (n = 14 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 32% (Mayfield & Dempsey 2026, Oceans, supplemental S1).

Stressors

Condition cannot be assessed at all: no usable photographs exist for this site (Anderson's sheet: "camera fogged up again, no good photos"; the dive also had figure-eight currents and poor visibility, and the diver was separated from the group), so there are no CoralNet or Coralscapes products, no multi-method comparison, and no photographic observation of bleaching, disease, predation, crown-of-thorns, or fauna — these are unavailable, not zero. No mean bleaching value was published for this site in either CoralNet training run, so the site contributes nothing to any archipelago bleaching statistic. Anderson's sampling sheet records three pocilloporid colonies sampled here for a collaborator (species by field call): Pocillopora sp. ChJo132 (13.3 m, large, healthy), ChJo133 (15.6 m, dark pigmentation), and ChJo134 (14.2 m, 40% pale or sick; the sample was taken from its bleached tissue). 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). The Living Oceans Foundation transects here recorded no cyanobacteria and no recently dead coral; they carry no bleaching, disease, or crown-of-thorns field.

Comparisons with other data

Apart from the Living Oceans Foundation survey shown here, we found no other surveys at this site as of 2026. If you would like to share yours, please email us.