Superfast Evolution in Sea Stars

The sea stars Cryptasperina hystera and C. pentagona are close relatives with very different ways of reproducing but difficult to tell apart. A new study shows the species separated just a few thousand years ago. (Credit: Jon Puritz/University of Hawaii at Manoa)

How quickly can new species arise? In as little as 6,000 years, according to a study of Australian sea stars.

“That’s unbelievably fast compared to most organisms,” said Rick Grosberg, professor of evolution and ecology at UC Davis and coauthor on the paper published July 18 in the journal Proceedings of the Royal Society B.

Grosberg is interested in how new species arise in the ocean. On land, groups of plants and animals can be physically isolated by mountains or rivers and then diverge until they can no longer interbreed even if they meet again. But how does this isolation happen in the wide-open ocean?

Grosberg and colleagues studied two closely related “cushion stars,”Cryptasperina pentagona and C. hystera, living on the Australian coast. The animals are identical in appearance but live in different regions: Hystera occurs on a few beaches and islands at the far southern end of the range ofpentagona.

And their sex lives are very, very different. Pentagona has male and female individuals that release sperm and eggs into the water where they fertilize, grow into larvae and float around in the plankton for a few months before settling down and developing into adult sea stars.

Ports host invasive sea star orgies

The study shows that man-made structures such as wharfs are hotspots for invasive sea stars to breed.

Marine biologists have found that port environments are enabling invasive sea stars to breed in Australia at a rapid rate.

In a new research article, researchers found that these environments can facilitate the invasion of a significant marine pest by driving overwhelming reproductive success.

Dr Scott Ling, from the UTAS Institute of Marine and Antarctic Studies (IMAS), is the lead author of the paper published in Journal of Applied Ecology.

“The sea star must release eggs in close proximity to sperm sources because chances of fertilisation decline drastically with increasing distance between spawning sea stars,” he said.

“Beneath wharves a super abundant supply of food leads to a veritable orgy of highly aggregated and fecund sea stars that achieve great fertilisation success”.

Dr Ling said the research found that wharf populations, while representing less than 10 per cent of the total sea star population in an estuary and concentrated in less than 0.1 per cent of the estuary area, can contribute up to a massive 90 per cent of all larval production in an estuary.

“A big part of the problem is that in human-dominated environments, very few native species compete with the invasive sea star,” he said.

Dr Ling said that while long-term protection of key sources of larval production is a common goal in marine reserve design and fisheries management, the same ecological concept, but in reverse – whereby larval production is minimised at key sources – is a concept yet to be broadly applied to the management of established marine pests.

“Restoring natural heritage values to achieve a more natural ecological balance in marine environments makes sense on many levels – here we have an example of what might be achievable to reduce the dominance of an exotic pest.

“While transfer of marine pests has increased globally with international shipping, the success of species once they arrive in new places can largely be determined by the ecological dynamics of the system they find themselves in,” Dr Ling said.

“There are consequences when we modify the marine environment, and exotic species can and will capitalise on opportunities to flourish.”

Full paper can be viewed online.