Chagos Archipelago - Great Chagos Bank West (BITB47)

Setting

BITB47 is a lagoonal patch reef inside the Three Brothers lagoon, leeward on Anderson's field sheet, surveyed 24 March 2015 on a dive to 30.6 m: 53% coral against 37% algae, with 29 genera.

General benthic features

Only 5.8% of the benthos is bare substrate and 4.0% non-coral invertebrates. Acropora leads at 16% of the benthos and Porites at 11%, together 51% of all coral. The depth profile is the finding: cover climbs monotonically 48%, 55%, 58% while algae falls 44% to 24%, the middle stratum is the diversity peak carrying every one of the site's 29 genera, and leadership hands over at the bottom, where Porites jumps to 25% of the benthos, 43% of that stratum's coral and four times its mid-depth value, pushing Acropora into second. The blue coral Heliopora occurs at the middle stratum and nowhere else.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• 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 37% of the benthos.
• Transect mean 53 ± 3.1% SE (n = 17 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 54% (Mayfield & Dempsey 2026, Oceans, supplemental S1).
• With only two photographs, the image-based estimates in the method table are not a basis for comparison; the transect figure is this site's cover value.

Stressors

Published bleaching is 5.56% (CoralNet analysis of the survey images; Mayfield & Dempsey 2026, suppl. S1). Condition, though, cannot really be assessed from images: the camera housing fogged, so the photographic record is two frames (Anderson's sampling sheet: no good pictures of the colonies because of camera fogging). They show a dense mixed high-cover mosaic and one large gold table colony carrying an older partial-mortality lesion already colonized by coralline algae; no bleaching field, crown-of-thorns, or disease is visible, but from two frames that is weak evidence (e.g., Image 1, Image 2).

12

Anderson's sampling sheet records eight colonies sampled here at 11.6–30.5 m: one Pocillopora acuta by RFLP; three Seriatopora hystrix and one P. acuta by field call; three Pocillopora sp. sampled for a collaborator (field calls); the condition notes run from healthy to 30% bleached. 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 0.2% cyanobacteria and no 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. If you would like to share yours, please email us.

Other notes

Aspect follows Anderson's field sheet (LOF fellowship 2016 workbook: 'lagoonal patch reef', 'leeward'); the expedition's 933-site table classes the station as 'protected' (patch reef). Esri World Imagery (no LOF habitat map covers this station; the LOF Chagos habitat map covers only Peros Banhos) shows open water at the pin about 17 km northeast of North Brother, on the Great Chagos Bank; no bottom or reef edge is visible, so the imagery cannot test the aspect.