Chagos Archipelago - Speakers Bank (BISP100)

Setting

BISP100 is a high-cover but visibly patchy forereef — 53.9% transect coral cover, 19th of the 109 Chagos sites, against only 24.5% algae (100th of 109, so among the least algal-dominated reefs surveyed).

General benthic features

Bare substrate is the notable substrate figure at 19.4%, with turf 11.8%, coralline algae 5.8%, non-coral invertebrates 2.3%, macroalgae 2.0%, and erect algae 0.5%. The assemblage is strongly Acropora-led across 16 non-zero genera. Acropora holds 41.44% of the benthos — 77% of all coral recorded — then Porites 3.45%, Montipora 2.81%, Favia 1.33%, Pocillopora 1.21%, Astreopora 0.95%, Leptastrea 0.68%, and Goniastrea 0.58%. Seven further genera sit below 0.5%: Psammocora, Montastrea, Favites, Hydnophora, Platygyra, Acanthastrea, and Cyphastrea. The site mean of 41.44% Acropora therefore averages a moderately diverse shallow band onto a deep near-monoculture and should not be quoted alone. The reef architecture alternates between locally dense coral patches and open framework. One frame shows several overlapping tables and branched colonies set at different heights, producing shaded cavities and small fish refuges (e.g., Image 4); two others show the same arrangement at wider scale, with live plates spaced by pale pavement and older irregular substrate. (e.g., Image 3) Assemblage composition.

43

Formal surveys give 53.9% coral, 24.5% algae, and 2.3% non-coral invertebrates, the coral 77% Acropora and reaching 64% of the benthos on the deepest transect alone. The photographs document a patchy canopy of overlapping tables and branching colonies separated by pale pavement, one partly bleached colony, and a large holothurian.

Coral cover

Cover doubles with depth and the assemblage narrows sharply as it does. D3 carries 36.7% coral across 15 genera, with Acropora at 17.33% and a genuinely mixed runner-up field — Montipora 4.44%, Porites 4.35%, Astreopora 2.85%. D4 rises to 53.0% across only six genera with Acropora at 43.00%. D5 reaches 72.0% coral across just three genera — Acropora 64.00%, Montipora 4.00%, Porites 4.00% — on 7.0% algal cover. One frame is notably more open and is the one that best explains why a 53.9% site figure should not be attached to every view — the retained sequence supports a patchy rather than uniformly continuous canopy, which is also what the 19.4% bare-substrate figure records. (e.g., Image 1) No photographic cover estimate was made from these contrasts.

1

Stressors

(e.g., Image 1) Coral condition is generally pigmented. The clearest condition frame is one in which much of a compact branching colony remains brown while numerous branch ends and several larger patches are white. (e.g., Image 2) (e.g., Image 2) Some of that could be normal growth margins, but its breadth across the colony makes partial bleaching plausible at medium confidence.

2

The overlapping-table frame contains additional pale-tipped branches where lighting and distance reduce certainty. The published figure of 4.8% ranks 72nd of 98 — low, and consistent with this reading. An important interpretive caution applies to this site's open frames: much of the pale ground is old skeletal material or sediment, not bleached tissue, distinguishable by its irregular eroded texture rather than intact coral surface. No crown-of-thorns starfish (COTS) or other corallivores evident.

Fish and other fauna

The clearest condition frame also holds a large dark reticulated sea-cucumber-like animal beneath the colony; the robust cylindrical body and patterned surface support an echinoderm, but the frame does not warrant a species name. Small black-and-white fishes shelter among the branches.

Comparisons with other data

No prior survey data from this site. If you would like to share yours, please email us.