Crown-of-thorns seastars, where do they go after an outbreak?

Crown-of-thorns seastars (Acanthaster planci, COT) are coral-feeding echinoderms, natural inhabitants of Indo-Pacific tropical coral reefs. They are cryptic and normally not prominent on reefs. However, when they form aggregations of hundreds to hundreds of thousands of individuals, an outbreak occurs, which may lead to devastating effects on reef-building corals. An outbreak can wipe out a whole reef ecosystem.

Where do they go after an outbreak? Spicule evidence suggests that they die and disintegrate near reefs (Walbran et al., 1989). However, mass deaths have not been observed (Moran, 1988), until recently. In January 2012, a large aggregation of dead crown-of-thorns starfishes was observed on the sandy beach of Urasoko Bay, Ishigaki Island in southern Japan (Suzuki, et al., 2012). This report provides the first concrete evidence of this phenomenon after they have depleted food source, e.g., reef-building corals.

Photo taken from Suzuki et al. (2012)

SOURCES:
Moran, P.J. 1988. The Acanthaster phenomenon. Australian Institute of Marine Science Monograph Series 7: 178 p.

Walbran, P.D., Henderson, R.A., Jull, A.J., Head, M.J. 1989 Evidence from sediments of long-term Acanthaster planci predation on corals of the Great Barrier Reef. Science 25:847–850.

Suzuki, G., Kai, S., Yamashita, H. 2012. Mass stranding of crown-of-thorns starfish. Coral Reefs. doi:  10.1007/s00338-012-0906-z.



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