Chagos Archipelago - Great Chagos Bank West (BITB46)

Setting

BITB46 is a protected submerged bank reef inside the Three Brothers lagoon at 27 m, surveyed 23 March 2015, and it is the low-cover site of its group: 25.8% coral against 55.3% algae, 84th of 109 Chagos sites for cover and 13th for algae (e.g., Image 17, Image 23, Image 30, Image 33).

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General benthic features

But algae here means something specific — crustose coralline algae alone is 29.1% of the benthos, the 4th-highest value of all 109 sites, so more than half the algal budget is hard pink-mauve pavement rather than fleshy weed, and the photographs show a well-grazed crust binding rubble and dead framework, not a degraded weedy reef (e.g., Image 1, Image 8, Image 10, Image 12, Image 22, Image 24).

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Across 22 genera, 69th of 109, Porites dominates at 11.35% of the benthos, 44% of every coral point and nearly three times the next genus.

Coral cover

The two strata differ more sharply than anywhere else in this group: cover more than halves from 35.1% to 16.5% while Acropora collapses 95% from 7.36% of the benthos to 0.40% and Porites comes to hold 58% of the deep stratum's coral — but that stratum rests on two transects, so it is descriptive rather than a demonstrated depth effect. Image methods read 7 to 10 points lower (CoralNet 18.8%, Coralscapes 16.2%) on a scored subset of only 11 frames, and should not be averaged.

Stressors

Bleaching is 2.02% on the site table's Mean(%bleaching) column, 89th of the 98 sites carrying a value, and both runs agree, so the canonical % bleaching (2nd training) figure is the same. All 29 frames were reviewed with no acute bleaching field anywhere; one very large table carries sharply bounded partial mortality across 40% of its plate, already colonized by coralline algae and so an older lesion (e.g., Image 4).

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No crown-of-thorns, disease, or predation.

Fish and other fauna

Fauna is exceptional: a gray reef shark and a whitetip reef shark, surgeonfish and fusilier schools, a baitfish cloud, and a giant clam (e.g., Image 2, Image 3, Image 5, Image 6, Image 9, Image 11, Image 13, Image 14, Image 16, Image 18, Image 20, Image 21, Image 25, Image 26, Image 27, Image 29, Image 32).

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Comparisons with other data

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