DIE-OFF, STARFISH - JAPAN: STARVATION
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Date: Mon 4 Jun 2012
Source: BBC NATURE [edited]
<http://www.bbc.co.uk/nature/18294729?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed>
Hundreds of crown-of-thorns starfish found on a beach in southern Japan in January [2012] stranded themselves because they were starving, say researchers. More than 800 were discovered on a 300 meter stretch of sand on Ishigaki island.
The starfish population "outbreak" was 1st identified in 2009, when masses of juveniles were seen feeding on the island's outer coral reef. The coral-eating starfish then took 3 years to move onto the beach, where they perished.
The reason for the starfish population boom is not clear, but the strange behaviour has shown marine scientists what can happen when these slow-moving creatures completely deplete their food source. "The shortage of food, corals, is a probable cause of the stranding," said Go Suzuki from the Fisheries Research Agency, who witnessed the phenomenon from his research station. In a paper, published in the journal Coral Reefs, Mr Suzuki and colleagues described how an area once covered with up to 60 per cent coral was reduced to one per cent by the voracious starfish.
The marine scientists described how the starfish gradually moved closer to the beach, possibly in search of more coral to feed on. Mr Suzuki suggested that the current may have helped the starfish along their doomed path, pushing the animals towards the shore. Noting that they died on the beach rather than in the water, the team concluded that when the starving starfish were eventually washed up, they were too weak to return to the sea.
The multi-armed starfish are named for the protective venomous spines that cover their surface like a crown. The predators extrude their stomachs in order to feed. They liquefy their prey with digestive juices, absorb the nutrients and then suck their stomachs back in.
Adults can consume as much as 6 square metres of living coral reef per year.
[byline: Ella Davies]
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[The paper cited in the text can be accessed at <http://www.springerlink.com/content/wj848pjql8247073/>.
The crown-of-thorns starfish, _Acanthaster planci_, is a large multi-armed echinoderm that usually preys upon coral polyps (especially _Scleractinia_). The crown-of-thorns receives its name from poisonous thorn-like spines that cover its upper surface (see picture at <http://upload.wikimedia.org/wikipedia/commons/8/8f/CrownofThornsStarfish_Fiji_2005-10-12.jpg>).
It is the 2nd largest sea star in the world. _A. planci_ has a very wide Indo-Pacific distribution. It occurs at tropical and subtropical latitudes from the Red Sea and the east African coast, across the Pacific Ocean, across the Indian Ocean, and the west coast of Central America. It occurs where there are coral reefs or hard coral communities in this region.
Massive population collapses following depletion of food sources are also observed in other animal species (for example, Soay Sheep in Scottish archipelagos), and usually occur in simple ecosystems in which a small number of species occupy existing ecological niches.
This phenomenon might be an indication of an underlying ecosystem health problem.
A picture of the stranded starfish can be seen at <http://news.bbcimg.co.uk/media/images/60635000/jpg/_60635558_cots_strand_120130.jpg>.
A ProMED-mail/HealthMap of the affected area can be accessed at <http://healthmap.org/r/2xif>. - Mod.PMB]
[see also:
2008
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Undiagnosed die-off, starfish - UK 20080314.1016] .................................................sb/pmb/msp/sh/ll
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