Chagos Archipelago - Speakers Bank (BISP89)

Setting

BISP89 is a deep lagoonal patch reef inside Speakers Bank, windward from its position on the southeast side of Speakers Bank relative to the prevailing southeast trade winds (leeward on Anderson's field sheet), surveyed 24 April 2015 on a dive to 30.2 m (see Dive record below).

General benthic features

Twenty-nine coral genera were recorded, and the three depth strata hand the lead over twice: Acropora holds 54% of the coral in the shallowest stratum, Stylophora leads at mid-depth, and Porites leads in the deepest, where cover peaks and algal cover falls away. The photographs show coral-abundant branching patches (e.g., Image 2) alternating with open plate-and-rubble pavement (e.g., Image 3) and mixed fish schools (e.g., Image 11, Image 13).

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Stark-white branching colonies and plates stand beside pigmented brown tables, with pale cream-yellow tables behind them in Image 10 and Image 12, as Anderson's dive notes record: all Seriatopora bleached, nearly everything bleached and dying around 15 m, and a black slimy sponge growing on everything (see Dive record below).

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Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Formal transects recorded 34% coral cover against 54% algae.
• Transect mean 34 ± 3.7% SE (n = 16 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 33% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• The bleaching percentage is a computer vision figure: CoralNet annotation of the informal survey images, not a diver's field estimate (Mayfield & Dempsey 2026, suppl. S1).

Stressors

The published image-based bleaching figure is 9.2%; of the seven colonies Anderson sampled here, five were partly to fully bleached and one more was pale and sickly (see Dive record below). The Living Oceans Foundation transects here recorded no cyanobacteria and under 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. If you would like to share yours, please email us.

Dive record

Anderson's morning dive on 24 April 2015 entered the water at 09:11 and lasted 53 minutes, to a maximum depth of 30.2 m (the field sheet); the notes describe a back-reef pinnacle that looks like a lagoonal patch reef, technically part of the main bank structure, cresting at 12-13 m, with nicer corals at 20-30 m, many bleached or dead corals, nearly everything bleached and dying around 15 m, all Seriatopora bleached, a black slimy sponge growing on everything, and a mild current. Anderson sampled two Pocillopora acuta colonies (confirmed by RFLP): CHPd114 (collected 09:20 at 28.5 m; sickly and pale, uncommon at the site) and CHPd115 (09:39, 19.0 m; 10% bleached and sickly, possibly diseased, the only colony seen at 20 m). Anderson sampled three Seriatopora colonies (field calls): ChSe125 (S. hystrix; 09:15, 30.0 m; pale neon green, 100% bleached, live tissue still evident; most colonies at 25-30 m were 100% bleached), ChSe126 (S. hystrix or S. aculeata; 09:24, 25.9 m; 100% bleached, live tissue still evident), and ChSe127 (likely S. aculeata; 09:35, 21.0 m; very small, 100% bleached, live tissue still evident). For a collaborator Anderson also sampled two Pocillopora sp. colonies: ChJo227 (09:45, 15.3 m; healthy, with some old and new mortality) and ChJo228 (09:50, 15.5 m; in the early stages of bleaching, about 15%). 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

Anderson's field sheet records the aspect (LOF fellowship 2016 workbook: 'lagoonal patch reef', 'leeward'); the expedition's 933-site table classes the station as 'protected' (patch reef). The aspect shown, 'windward', comes from the station's GPS position on the southeast side of Speakers Bank relative to the prevailing southeast trade winds (about 7° off the upwind direction; the reef-edge reading agrees), which takes precedence over slope facing, lagoon shelter, imagery, and field labels. Esri World Imagery (no LOF habitat map covers Speakers Bank; the LOF Chagos habitat map covers only Peros Banhos) puts the pin among patch reefs inside the south-east Speakers Bank lagoon, consistent with the sheet.