It has been established by folks who observe these things that the swarm of “medusas” – Jellyfish – arrive on Israel’s shores around Tamuz 17 and floats away after 9 B’Av – the three weeks that mark the period between the time the Romans breached the walls of Jerusalem and the burning of our holy Temple in the year 70 CE. And since Jewish halakha recommends avoiding frequent bathing unsafe activities during the three weeks, and swimming is considered an unsafe activity as well as bathing, it looked as if nature has gone out of its way to keep us from transgressing.
Not anymore. In contrast to previous years, when at this time of the year huge swarms of jellyfish already reach the shores of Israel, the beaches this year are almost completely free of jellyfish. University of Haifa researchers estimate that this situation could remain throughout the beach-going season and Israelis will experience a summer that’s almost free of jellyfish.
“Based on previous years when the jellyfish arrived late and we had small summer swarms, we may see this phenomenon again this year – a large and dense swarm will not reach us,” said Dr. Dor Adelist from the Department of Maritime Civilizations at the University of Haifa.
“We say this with caution and of course, the reality can still change, but if you look at past cases, this is certainly the reasonable estimate, as of this moment,” he added.
So far, the only reports on heavy jellyfish presence have come from Spain.
“In previous years, we would already be receiving reports from yachtsmen and trawlers who are in the middle of the sea, that the jellyfish are on their way to us. In the meantime, they also say that the sea is free of jellyfish,” says Prof. Dror Angel, also from the Department of Maritime Civilizations at the University of Haifa.
Dr. Gur Mizrahi from the Charni School of Marine Sciences at the University of Haifa reported a similar picture, this time from a bird’s eye view. In a study led by Dr. Yoav Lehn from the School of Marine Sciences, they are used to identifying the swarm of jellyfish with the help of a light plane, then sailing over it to study it in depth. Dr. Mizrahi went up in a plane at the beginning of this week and saw a sea clear of the white, stinging animals.
“The area we surveyed from the air was very wide. We flew 6 miles from the coastline and along all the beaches and no swarms of jellyfish were observed. We saw a few jellyfish that may have remained in the area from winter and spring,” said Dr. Mizrahi, who also predicted with a high probability that this summer will be relatively free of jellyfish.
So, why aren’t the jellyfish coming? One possibility is a change in ocean currents, which may have swept the jellyfish to other areas. However, according to the researchers, they haven’t seen reports of swarms of jellyfish in other places, where they could have reached due to a change in the currents.
Also, the northern current, which can perhaps sweep the jellyfish to the shores of Israel and also to more distant areas, was weak this year, so perhaps the changing currents are indeed part of the explanation for the phenomenon.
The main assessment on which the researchers agree is that climate change caused the seawater to warm more slowly this year and therefore the comfortable temperature for the polyps to “ripen” into jellyfish was delayed by about two weeks. In light of this, the initial assessment of Prof. Angel and Dr. Edelist was that the jellyfish would also be late for a similar amount of time. But time passed and the jellyfish refused to show. So, what happened?
“We still estimate that the reproduction process of the jellyfish did take place two to three weeks late, but it is possible that when they did mature, another factor came into the picture, for example, an animal that preys on the jellyfish when they are still small. Of course, other things may have happened, because the sea is a complex and complicated system,” said Prof. Angel.
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The years 2016, 2018, and 2021 also saw a smaller jellyfish migration.
“There is no doubt that a summer without jellyfish is great news for bathers, but if anyone thinks this is the end of the jellyfish, they are mistaken,” concluded Prof. Angel. “What happened this year does not say anything about the population of jellyfish that sit on the sea floor, still in the polyp stage. Most likely, the polyp colonies are still waiting for the right conditions to hatch and release mature jellyfish into the sea. So, for all we know now, jellyfish aren’t going to disappear. This year is just a slight smack on in the wing for them.”
