[Coral-List] COTS in Chagos

Ronan Roche ronanroche at gmail.com
Fri Sep 25 08:22:49 EDT 2015

Dear All,

Given some of the recent discussions on COTS on coral-list, this recent
publication in Marine Biology may be of interest to some readers.


If you would like a copy of at the pdf, please contact me directly.

Many thanks,

Ronan Roche

Outbreaks of the crown-of-thorns starfish (COTS), *Acanthaster planci*,
have occurred at many locations throughout the Indo-Pacific and are a major
contributor to widespread coral loss and reef degradation. The causes of
outbreaks remain controversial, but are commonly attributed to
anthropogenically elevated nutrients and/or over-fishing. If so, it seems
unlikely that outbreaks would occur in reef systems that are largely
isolated from anthropogenic disturbances. However, high densities of COTS
were recently observed on reefs in the Chagos Archipelago, a remote group
of atolls and banks within the central Indian Ocean, which experience very
limited anthropogenic influence. Aggregations of COTS were first noticed at
Eagle Island in 2012, which, although unquantified, appeared to be at
outbreak levels, and very high densities (1624 km−2) were subsequently
recorded at Danger Island in 2013. While these islands are uninhabited by
humans, it is possible that nutrient inputs result from upwelling zones
around the Archipelago, or high densities of breeding seabirds. Among
islands within the Great Chagos Bank, densities of the red-footed booby *Sula
sula* ranged from 8 to 7888 individuals km−2, with associated guano input
ranging from 96 to 25,381 kg island−1 year−1. However, Danger and Eagle
Islands where high COTS densities were recorded, had both high and low
levels of guano production, respectively, which suggests that outbreaks may
not be directly linked to guano nutrient enrichment. Other factors which
might be responsible for intermittent COTS outbreaks should be considered
in isolated reef systems such as the Chagos Archipelago.

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