Chagos Archipelago - Great Chagos Bank West (BIEA17)

Setting

BIEA17 is a protected emergent fringing reef inside the Eagle Island lagoon at 29 m, dived 14 March 2015 — and it is the poorest site at Eagle Island and third-poorest in the archipelago.

General benthic features

Twelve genera still resolve, led by Porites at 2.29% of the benthos, 47.8% of live coral, and Pocillopora at 1.06%, while Acropora is near-absent at 0.07% on a lagoonal fringing reef where it would normally lead.

Coral cover

Fifteen transects recorded 4.8% coral against 59.7% algae: 107th of 109 Chagos sites for cover and 7th of 109 for algae, the top decile, with 21.6% bare substrate. The site is severely patchy, the standard deviation exceeding the mean over a 0.0% to 31.0% transect range, one patch carrying nearly all the coral. The transect figure is its only cover number. Coral cover: 4.8%. Live hard coral measured on the in situ benthic transects of the LOF BIOT-1 expedition (Mayfield & Dempsey 2026, Oceans, supplemental S1), against algal cover of 59.7% of the benthos. The transect figure is this site's authoritative cover value; no image-derived product overrides it.

Stressors

The explanatory number is a single one: sediment-laden turf takes 44.42% of the benthos, the highest value of all 109 Chagos sites and six times the dataset mean, so nearly half the reef is turf bound with sediment and coralline algae is correspondingly halved. This is sediment retention, not macroalgal overgrowth. Coral falls twentyfold down the profile, 10.17% to 3.70% to 0.50%, as Porites hands over to the Chagos-endemic Ctenella and then to almost nothing; the sediment-turf maximum and the coralline minimum both land on the middle stratum, which is where the reef is most thoroughly smothered. Recently dead coral reads exactly zero on every transect, so the loss is not recent. No crown-of-thorns starfish (COTS) or other corallivores evident.

Comparisons with other data

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

Other notes

Condition cannot be assessed: Anderson dived this site but no imagery survives anywhere — a genuine photo loss rather than an undived site, worth a check of any unindexed 14 March camera cards. There are therefore no CoralNet or Coralscapes products, and the published Mean(%bleaching) cell is blank.