The warty comb jellyfish (Shevy Rothman)
The warty comb jellyfish, photographed off Shave Zion: Don't worry, it doesn't sting. Photo by Shevy Rothman, Tel Aviv University
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Wikimedia
A Pelagia noctilucas: they come, they go. In April lots of them came, and went. Photo by Wikimedia

The beautiful gelatinous sea-creature with the unbeautiful name of "warty comb" was observed in Israeli waters two months ago for the first time. The first sighting was off Nahariya, a city in northern Israel, and more were seen by the southern port city of Ashdod.

That doesn't mean the warty combs are here to stay, though, explains oceanographic ecologist Dr. Hadas Lubinevsky of the Israel Oceanographic and Limnological Research institute.

Just this April, she points out, Israeli bathers were startled to encounter Pelagia noctilucas, jellyfish that can helpfully glow in the dark and that are more commonly known as "mauve stingers" for their gentle colors (which can actually range from yellow to purple) and ungentle, venomous attack.

While the Pelagia do routinely exist elsewhere in the Mediterranean Sea, and a rare few appear in Israeli waters from time to time – they suddenly appeared in Israeli waters en masse and then disappeared at least for now, says Lubinevsky. They will, presumably, be back at some point.

Back to the warty comb. "It isn't new to the Mediterranean Sea," says Lubinevsky. "It abounds in the Atlantic Ocean and the western basin of the Mediterranean Sea, but this is the first time it's been observed in the eastern Mediterranean," which is where Israel is.

The Mediterranean Sea is contiguous but for scientific purposes, it can be divided it into eastern and western basins, which are connected by the narrow straits between Sicily and Tunisia. The physical conditions of the two Mediterranean basins are very different in many respects, including temperature and salinity.

The eastern basin is warmer and saltier, while the west is cooler and less saline, explains Lubinevsky.

In other words, if an animal accustomed to living in the western basin – like our warty jellyfish – finds itself in the eastern basin, it won't feel comfortable.

Also, while there is no longer any doubt that the world's oceans are slowly warming up with the process of global warming, that would affect both basins roughly equally. The temperature gradient between the west and east basins would be roughly maintained.

Since the warty comb, like the mauve stingers that preceded it, are both passive riders of currents (as opposed to, say, sea turtles that actively swim where they please), they could theoretically have been brought from west to east by a change in currents. Dr. Isaac Gertman, a Moscow-born physicist at the Israeli oceanographic institute, explains that west-to-east currents in the Mediterranean Sea aren't being measured by the institute, so it's not clear whether they have been changing (for instance pursuant to climate change) in a way that would move drifting animals like the warty comb into new territory.

It is equally possible that the appearance of the harmless gelatinous beauties is yet again an artifact of man – that they were brought in ballast water spilled in Haifa Bay by ships.

It isn't rare for ships to inadvertently transport species across oceans. An infamous example is the zebra mussel, which was accidentally introduced into North America from the Black Sea by a cargo ship. The zebra mussel proceeded to wreak havoc in the Lakes and are now proliferating merrily, at the expense of local mussels, from Canada to Mexico.

Meanwhile, it's way too soon to call the warty comb a new species in Israeli waters. Maybe they'll never be see again off Israel's coasts. Or maybe there are a few individuals lurking that will suddenly bloom, laughs Lubinevsky. Only time will tell.