Chagos Archipelago - Great Chagos Bank West (BIEA17)

Setting

BIEA17 is a protected emergent fringing reef inside the Eagle Island lagoon, dived to 27.5 m on 14 March 2015.

General benthic features

Twelve genera still resolve, led by Porites at 3.2% of the benthos, 50% of live coral, and Pocillopora at 1.4%, while Acropora is near-absent at 0.1%.

Coral cover

• Reference: Mayfield & Dempsey (2026)
• CoralNet submission package
• Fifteen transects recorded 6.3% coral against 60% algae, with 20% bare substrate.
• The site is severely patchy, the standard deviation exceeding the mean over a 0.0% to 31% transect range, the 31% transect alone carrying about a third of all the coral recorded.
• The transect figure is its only cover number.
• Live hard coral measured on the in situ benthic transects of the LOF BIOT-1 expedition (the mean of all of this station's transects), against total algal cover (all algal groups) of 60% of the benthos.
• The transect figure is this site's authoritative cover value; no image-derived product overrides it.
• Transect mean 6.3 ± 2.2% SE (n = 15 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 4.8% (Mayfield & Dempsey 2026, Oceans, supplemental S1).

Stressors

The explanatory number is a single one: sediment-laden turf takes 47% of the benthos, 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% to 3.7% to 0.5%, 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. The Living Oceans Foundation transects here recorded 0.1% cyanobacteria.

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.

Other notes

Condition cannot be assessed from photographs: Anderson dived this site but no imagery survives. The sampling sheet records one of the two Pocillopora colonies sampled here as 5–10% bleached or dead and the other as large and healthy. Anderson's sheet records no P. damicornis or P. acuta at this site; these colonies were collected for a collaborator. Pocillopora acuta colonies from elsewhere in the archipelago were analyzed in Thomas et al. (2026, Global Ecology and Biogeography 35:e70305, https://doi.org/10.1111/geb.70305). There are therefore no CoralNet or Coralscapes products, and no published mean bleaching value for this site.

No underwater photographs from this station are on file.