Crown of thorns starfish (COTS – Acanthaster planci) are notorious throughout the Indo-Pacific region. COTS are voracious coralivores, and in outbreak proportions can eat vast areas of reef by exuding their stomachs and digesting coral polyps (read more). Having been diving in oceans around the world over the past few decades, i’ve often pondered the differences in colourations of COTS between reef regions, and whether they represented a single species. A recent paper published in Biology Letters by Catherine Vogler from Göttingen University and colleagues at the Smithsonian and University of California confirms that COTS aren’t a single taxonomic entity, and in fact represent a ‘species complex’ of upto four seperate species.

Different appearances of the Crown of Thorns starfish across locations, clockwise from Top Left: Madagascar (Image credit: Mila Zinkova), Thailand (Image credit: Jon Hanson) Okinawa, Japan (Image credit: Gary Hughes), Fiji (Image credit: Matt Wright)

Using a genetic approach, the researchers analysed DNA from over 237 starfish collected from reefs around the world. Their results strongly suggest that their are in fact four species of COTS, located in the Pacific Ocean, Red Sea, Southern Indian Ocean and Northern Indian Ocean).

Geographical distribution of the different species of crown of thorns (each colour represents a different species where sampled, piecharts indicte the frequency of each species per location)

It’s fascinating to think that the divergence of these species occured between the Pliocene (3.65 million years ago) and early Pliestocene (1.95 million years ago). More importantly though, this discovery may have fairly interesting implications for conservation biology. The researchers point out that whilst outbreaks of COTS are well-researched phenomena on the GBR and Indo-Pacific reefs since the early 1960’s, outbreaks in the Indian Ocean and Red Sea are much less severe. It seems that a better understanding of the genetic structure of COTS populations and identifying species boundaries may go a long way to explaining the intensity and magnitude of COTS outbreaks in different regions.

Reference: Vogler et al (2008) A threat to coral reefs multiplied? Four species of crown of thorns starfish. Biology Letters doi:10.1098/rsbl.2008.0454 (Link)