Could the ocean turn to jelly?

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Overfishing may have an unexpected result – it could lead to jellyfish taking over the oceans!

Scientists from Spain and the US have found that while jellyfish might seem slow, and certainly no match for a top marine predator, they actually consume prey at a similar rate to that of swimming and hunting fish.

A consequence of this has been that in areas where populations of fish such as sardines and anchovies have been overfished or reduced due to habitat destruction, jellyfish have become the dominant predators, suggesting a future "gelatinous ocean" if these habitat pressures continue. 

The results of the study are unexpected as jellyfish hunt by floating and bumping into their prey. In theory it was expected that fish should easily out-compete any jellyfish but José Luis Acuña and his colleagues found that jellyfish consume prey at roughly the same rate as the fish and use around the same amount of energy as they float around the currents.

There are also concerns that they are evolving larger, water filled bodies to enable them to come into contact with more prey whilst still floating at a relatively slow speed, which in turn allows them to capitalise on any changes to the ecosystem due to overfishing.

The study also follows on from worrying research earlier this year by a separate group of scientists that showed that the proliferation of jellyfish could lead to an alarming cycle of ocean acidification as not only do jellyfish consume huge quantities of plankton but when they die, but they break down into a form of carbon which is released as carbon dioxide.

For more information see: Faking Giants: The Evolution of High Prey Clearance Rates in Jellyfishes José Luis Acuña, Ángel López-Urrutia, Sean Colin. Science 16 September 2011: Vol. 333 no. 6049 pp. 1627-1629  DOI: 10.1126/science.1205134

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