New Medusa Provides Evidence for Changes Taking Place in the Mediterranean Sea

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Meet our guest, glowing a phosphorescent shade of green: a new jellyfish which has arrived from Japan and was observed for the first time in the Mediterranean Sea during a routine survey conducted by Dr. Gur Mizrahi, a researcher from the laboratory of Dr. Dan Tchernov in the Leon H. Charney School of Marine Sciences: the Aequorea macrodactyla (Cnidaria Hydrozoa), a species of medusa spotted repeatedly in the Sea of Japan. The good news: This medusa is not dangerous to humans. The bad news: its arrival heralds 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. Mizrahi.

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 Dr. 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, the medusa’s body, measuring only a few centimeters, is composed of 98% water, so when it is encountered as isolated individuals, it is almost impossible to discern. Despite its phosphorescent color, it has a much more fascinating feature: “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 explained.

The most obvious question is how did this jellyfish get 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. However, having conducted what are termed “phylogenetic” tests which utilize genetic “markers” and thereby enable the researchers to determine patterns of migration, and isolate migrant species from local ones, Dr. Mizrahi is of the opinion that the most logical explanation is that this jellyfish was indeed brought to our region within the ballast water of ships: “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 explained.

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.”

Something already apparent from Dr. Mizrahi’s study is that the presence of this jellyfish in the eastern basin of the Mediterranean Sea can affect the region’s marine environment. As this species has joined the local fish populations, it now competes with them for the same food supply, specifically plankton and small crustaceans, “but probably not significantly,” says the researcher whose article, written jointly with Dr. Eli Shemesh, will be published in the July 2015 issue of the scientific journal NeoBiota.

It should be noted that a relative of this very same jellyfish won the 2008 Nobel Prize in Chemistry for three researchers, a Japanese and two Americans, for their joint discovery of the protein known as GFP (Green Fluorescent Protein). This protein, which emits a fluorescent green light when exposed to ultraviolet radiation, has subsequently become widely used in research laboratories as a means of indicating processes as they occur in living organisms, such as the development of brain cells, the spread of cancer cells, or as a measure of genetic activity. In addition, the discovery of how this protein emits light has opened important doors to many different researchers who, following the discovery can now mark various different proteins by means of separate colors thereby enabling them to distinguish between different processes occurring simultaneously. Among other things, the protein is used to detect damage to nerve cells from Alzheimer’s disease, or to predict how cells which produce insulin are formed in the pancreas of a developing embryo.

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