New Invasive Jellyfish Spotted Off Israeli Coast

Glowing green Aequorea macrodactyla looks toxic but isn't – yet it could portend dangerous change in the Mediterranean Sea, says Haifa University expert

Ruth Schuster
Ruth Schuster
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Aequorea macrodactyla, fondly known as Cnidaria Hydrozoa, usually in the Sea of Japan and now at a beach off Israel.
Aequorea macrodactyla, fondly known as Cnidaria Hydrozoa, usually in the Sea of Japan and now at a beach off Israel. Credit: Research Institute of Marine Biotics
Ruth Schuster
Ruth Schuster

A jellyfish native to the Sea of Japan has been spotted in the Mediterranean Sea. Glowing an obnoxious green color, the thing looks like a nightmare from a sci-fi cartoon but actually, unless you're a plankton, it's harmless, according to Dr. Gur Mizrahi of Haifa University.

Here's another charming factoid about Aequorea macrodactyla: unlike you, it might be immortal. “This jellyfish belongs to a class of species which are able to stay young forever," says Mizrahi, a scientist at the laboratory of Dr. Dan Tchernov in the Leon H. Charney School of Marine Sciences. "Some 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."

What the bright green protein characterizing Aequorea does is anybody's guess, says Mizrahi, adding that the poor jelly doesn't have a nickname that anybody can pronounce yet. Why? "Maybe because it hides, so it remained anonymous," he laughed.

Aequorea is common in the seas of Japan and it lives throughout the water column – but it's transparent, Mizrahi points out. True, it glows bright green but it's small, just a few centimeters long. It likes to eat tiny sea creatures, including tiny crustaceans.

Mizrahi noticed the jellyfish, which is also known as Cnidaria Hydrozoa, during a routine survey, in two spots, no less – in Haifa Bay and further south opposite Beit Yanai, at a relatively shallow depth of just 10 meters.

The lovely Cnidaria Hydrozoa, close up. Credit: Courtesy of Evrogen

If this hard-to-spot animal has been sighted in two places, the thing could be everywhere. "That could indicate that it's become settled in the Mediterranean," Mizrahi says. And if they're floating around the sea, for some reason, they've reached the sexual stage of their life cycle (jellyfish can spend years in a sessile stage, quietly sitting in one spot and budding asexually).

The timing of their reaching the sexual stage is not clear – a given species may behave one way in one environment, and differently in a different environment, Mizrahi says.

How the beast arrived from the Sea of Japan to Haifa Bay is probably no mystery. It isn't rare for species to travel outside their comfort zone in the ballast water of ships.

A closeup of Aequorea macrodactyla, showing exactly why they can be hard to spot. Photo: Courtesy of University of Haifa

Hello, stranger

When it arrived is another question. It could have arrived a long time ago and simply not been noticed. They're pretty small and don't sting; also, it might have lived in the depths and only recently risen to the surface, the Marine Sciences school postulates. However, based on testing genetic markers and comparing with the home population in the Sea of Japan, Mizrahi feels this beast is fairly recent.

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

So what we have is a new jellyfish that harms nobody but micro-fauna and is quite pretty. However, it could portend something ugly indeed, which is that the fauna of the Mediterranean Sea is dramatically changing. A scientist through and through, Mizrahi points out that we cannot categorically state the change is for the worse, but it could well be.

Dr. Gur Mizrahi, surveying the Mediterranean Sea. Photo: University of Haifa

He points at the example of the Black Sea, inland Turkey, where overfishing and pollution created conditions for comb jellies to proliferate – which they merrily did, decimating what fish populations remained.

But the arrival of the glowing green orb-like animal to the local sea indicates two things. One: Man is transporting animals around in ways he shouldn't. Two: Danger looms.

If it were the one invasive species, he wouldn't be worried, says Mizrahi. "But the change to the Mediterranean fauna isn't confined to that. There is a dramatic, wider change, which leads us to say that something is happening." And while the Aequorea is harmless, if man continues to muck around with the marine environment, other jellyfish that are not benign at all, like the Portuguese Man of War or sea wasps, could show up. "We should take care not to allow our sea to become gelatinous as a result of human activities,” he warns.

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