Chagos Archipelago - Speakers Bank (BISP95)

Setting

BISP95 is a high-cover lagoonal patch reef inside the southern rim of Speakers Bank, leeward on Anderson's field sheet, surveyed 26 April 2015 on a dive to 22.6 m (see Dive record below); table coral, open rubble, and a seagrass meadow alternate across it.

General benthic features

Bare substrate is correspondingly high at 12%, with coralline algae 9.5%, turf 9.3%, macroalgae 1.8%, non-coral invertebrates 1.5%, and erect algae 0.7%. The assemblage is strongly Acropora-led across 15 non-zero genera. Acropora holds 51% of the benthos — 83% of all coral recorded — then Porites 3.1%, Pocillopora 2.8%, Heliopora 0.8%, Stylophora and Ctenella 0.7% each, Pavona 0.5%, and Platygyra 0.4%. Seven further genera fall below 0.5%. Algal cover barely moves (25%, 26%, 30%). The genus order is stable throughout — Acropora, then Porites and Pocillopora — so the site mean is a fair summary of composition, if not of cover. The seagrass meadow is the site's distinguishing habitat. One frame shows elongated ribbon-like blades rooted among coral and rubble, and a later run of frames shows a broad meadow occupying much of the benthos (e.g., Image 8, Image 21, Image 22).

82122

Anderson's field note calls it seagrass growing beside the coral, the first such sighting of the Chagos trip. The meadow provides a habitat wholly different from the table-coral patches and is the main reason the site reads as heterogeneous. Coral architecture is most developed in the first and middle portions of the sequence (e.g., Image 1, Image 3).

13

Two frames show overlapping tables with branching colonies in the gaps; two more retain table and corymbose forms but include more exposed substrate; another two show mixed coral patches reappearing after the open rubble views; and a final pair shows the rubble-dominated ground between them (e.g., Image 3, Image 16, Image 12, Image 18, Image 11, Image 20, Image 2, Image 23).

1612181120223

The habitat is patchy — locally broad living canopies coexisting with low-relief areas where carbonate debris and old framework dominate (e.g., Image 2, Image 4).

4

The photographs document a strongly patchy reef — table canopies, open rubble and pavement, and an extensive seagrass meadow — plus partly bleached branching colonies and a table with a broad white margin.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• 61%, against 26% algae, but the photographic sequence turns over sharply from table-dominated coral habitat through open rubble and pavement into a broad seagrass meadow.
• Transect mean 61 ± 4.8% SE (n = 12 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 57% (Mayfield & Dempsey 2026, Oceans, suppl. S1).
• Cover is flat across the two shallower bands and drops at depth.
• D2 carries 65% coral across 11 genera with Acropora at 53%; D3 is essentially identical at 65% across seven genera with Acropora at 57%; D4 falls to 41% across seven genera with Acropora at 30%.
• Formal surveys give 61% coral, 26% algae, and 1.5% non-coral invertebrates, the coral 83% Acropora with a stable genus order across all three depth bands.

Stressors

Published bleaching is 6.5% (CoralNet analysis of the survey images; Mayfield & Dempsey 2026, suppl. S1), and Anderson's field record shows more: 90%-bleached Pocillopora verrucosa colonies were very common at 20 m, and three of the four pocilloporids sampled were bleached or bleaching, two of them partly dead (see Dive record below). In the photographs, compact branching colonies are partly bleached, with white tops and brown bases (e.g., Image 15), and a table beside the seagrass has a broad white margin (e.g., Image 5).

155

The Living Oceans Foundation transects here recorded no cyanobacteria and 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. Within 5 km, three XL Catlin Seaview Survey stations recorded station-year means of 20–30% hard coral cover in 2015; the nearest, XL Catlin Seaview Survey at transect 36022, 1.99 km away, read 30% in 2015.

Dive record

Anderson's early-morning dive on 26 April 2015 entered the water at 08:16 and lasted 58 minutes, to a maximum depth of 22.6 m (the field sheet); the notes describe low-relief corals and low cover above 20 m, with table Acropora dominating below that, no P. acuta, P. damicornis, or Seriatopora, and seagrass growing adjacent to coral, “very strange (first time to see that in Chagos).” For a collaborator, four pocilloporids were sampled (species by field call): ChJo243 (likely P. verrucosa; collected 08:24 at 21.3 m; a huge colony, 90% bleached with pigmented areas still visible; very common at 20 m), ChJo244 (Pocillopora sp.; 08:29, 18.7 m; healthy, some green fluorescence), ChJo245 (Pocillopora sp.; 08:36, 19.1 m; 20% already dead, the rest bleaching), and ChJo246 (Pocillopora sp.; 08:46, 14.2 m; bleaching and partly dead recently, in a mostly coral-less area at about 15 m). 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

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 Speakers Bank; the LOF Chagos habitat map covers only Peros Banhos) puts the pin on the lagoon side of the southern Speakers Bank rim, consistent with the sheet.