June 28, 2015, Updated July 6, 2015
The jellyfish as seen without the green light. (University of Haifa, Courtesy)
The jellyfish as seen without the green light. (University of Haifa, Courtesy)

A green glowing phosphorescent jellyfish, usually spotted in Japan, was observed for the first time in the Mediterranean Sea during a routine survey by Israeli marine scientists. While not dangerous to people, its arrival shows evidence for changes taking place in the Mediterranean Sea and suggests that much more dangerous visitors can get here as well.

“This is a particularly unique jellyfish, as it contains a fluorescent green-colored protein the role of which, despite many theories, is still not clear to science. Despite its small body – just a few centimeters in length – it devours plankton and small crustaceans; but we can stay calm – as it’s not dangerous to humans,” said Dr. Gur Mizrahi, a researcher from the laboratory of Dr. Dan Tchernov in the Leon H. Charney School of Marine Sciences at the University of Haifa, who spotted the Aequorea macrodactyla (Cnidaria Hydrozoa) jellyfish.

A guest from Japan: Glowing green jellyfish arrives in Israel. (Photo: http://www.rimi.or.jp/engdobutu/FCNIDARIA.html)
A guest from Japan: Glowing green jellyfish arrives in Israel. (Photo: http://www.rimi.or.jp/engdobutu/FCNIDARIA.html)

This jellyfish was observed at two sites off the coast of Israel – in Haifa Bay and further south opposite Beit Yanai, at a relatively shallow depth of just 10 meters. According to Mizrahi, jellyfish can take advantage of the water column extending from the shallow sea down to significant depths of up to 1,500 meters.

In addition, this jellyfish’s body measures only a few centimeters and has found eternal youth.

“This jellyfish belongs to the class of species which are able to stay young forever. Jellyfish of this class can rejuvenate themselves: after having reached adulthood and borne offspring, they are capable of reverting to the state of an embryo,” he says.

Scientists are now wondering how this jellyfish got to the coast of Israel. One option is that the species arrived in the ballast water of merchant ships. A second possibility is that the jellyfish has actually lived for years in the depths of the Mediterranean Sea but now, for some unknown reason, it has ascended to shallower water.

“Beyond the results of the genetic and morphological analyses we conducted, additional evidence for this explanation is the fact that no such jellyfish have been found anywhere along the vast geographical distance extending between Japan and Israel. Or in other words, this jellyfish arrived here thanks to human intervention, and not naturally,” he said.

However, regardless of the reason for the appearance of this jellyfish in our vicinity, its very survival and even thriving here is one of the best proofs that the Mediterranean Sea in undergoing dramatic changes – which are potentially dangerous.

“These changes are mostly the result of man’s intervention in nature – overfishing may be leading to the dwindling of the medusa’s natural enemies; but its very presence here can also possibly attest to changes taking place on a more global level, such as the warming of the oceans. The concern is that changes to the marine environment will allow other jellyfish, dangerous to humans, to migrate to this area and cause significant and dramatic harm. We should take care not to allow our sea to become gelatinous as a result of human activities.”

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Jason Harris

Jason Harris

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