Jellyfish Swarms Correlated With Full Moon, Electric Company Worker Discovers

Israel Electric Corp worker found unexpected correlations between swarms of nomadica jellyfish, the temperature of the sea - and the phase of the moon.

Ruth Schuster
Ruth Schuster
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Avi Algazi, the Electric Corp worker who made a breakthrough discovery about jellyfish swarming. Avi is wearing a hard blue IEC hat, a red, white and blue plaid shirt with the top button undone, jeans, and is holding an ostensibly absurdly large - but actually average - specimen of the nomadica jellyfish, which, he discovered, swarms as a function of the water temperature and lunar cycle.
Avi Algazi, the Electric Corp worker and masters student who made a breakthrough discovery about jellyfish swarming.Credit: Avi Algazi
Ruth Schuster
Ruth Schuster

Power plants the world wide can be grateful to an electric company worker who has found a correlation between the full moon, water temperature and jellyfish swarming. Avi Algazi's breakthrough discovery could lead to ways to predict outbreaks by the primitive animals, which can arrive by the ton and paralyze power stations by clogging seawater intake pipes to cooling systems.

His findings relate to the Nomad (Rhopilema nomadica), a huge but harmless whitish jellyfish that has plagued Israeli shores since migrating to the Mediterranean from the Red Sea through the Suez Canal in the late 1970s. It has been a particular bane to his employer, the Israel Electric Corp.

The IEC has five seawater-cooled power stations along the Mediterranean coast. The stations have filters over seawater intake systems, which can get overwhelmed. "When jellyfish swarm, they clog the cooling system. We have to reduce production capacity or in extreme cases, shut down entirely to clean out the systems," Algazi says, poignantly adding that jellyfish swarming season, June-July, is the very time Israelis most depend on air conditioning.

Jellyfish being shunted away from the cooling systems at the Rotenberg power station.
Filtering against jellyfish  at the Rotenberg power station, 2015: At the Rotenberg power station, 2015: Picture shows a grid in the seawater intake system, against which large white jellyfish coming in with the seawater are starting to pile up.
Jellyfish swarm at the Rotenberg power station, 2015
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Jellyfish being shunted away from the cooling systems at the Rotenberg power station.Credit: Yossi Weiss, IEC
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Filtering against jellyfish at the Rotenberg power station, 2015Credit: Couurtesy of the Electric Corp.
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Jellyfish swarm at the Rotenberg power station, 2015Credit: Courtesy of Israel Electric Corp.
Jellyfish swarm

At first Algazi, 50-year-old married father of two, set out to study how jellyfish affect power stations. From 2006 to 2013, he collected data on the dates of swarms at the Eshkol Power Station in Ashdod, and on the sea temperature, measured at high resolution - several times a day, he explained to Haaretz.

He graphed swarming dates and sea temperatures, and wound up with a stark sinus chart.

It transpires that almost all, 94%, of nomadica swarms in Israel happen around mid-year when the Mediterranean Sea temperature ranges between 28.2 and 30 degrees Celsius. Exactly.

However, clearly there was some other correlation involved, because not every coincidence of mid-year and sea temperature produced jellyfish swarms. The missing correlation proved harder to pin down.

Power stations under attack

Individual jellyfish may come under other conditions, says Algazi. Who heads the communications department of the IEC's national load supervision department. A jelly here or there is nothing. The problem is swarming, when a power station finds itself under "attack" by tons of the things.

Having established the correlation between swarming and water temperature, Algazi tried to find statistically significant links between the jellyfish swarms at the Eshkol Power Station in Ashdod, and environmental factors such as wind direction and speed. That came to nothing.

His thesis guide, Prof. Abraham Haim of Haifa University was the one who suggested checking for correlation between the arrival of jellyfish swarms and the moon. (Algazi's work is guided by Haim with Dr. Keren Or-Chen of Haifa University and Dr. Anat Geffen Glazer of the IEC.)

Why? "Because of the great influence the moon has on the earth," Algazi explains to Haaretz. The notion isn't that far-fetched: the full moon may not trigger werewolf metamorphosis or insanity in New Yorkers, but has been linked with biological phenomena, such as mass spawning by coral, for instance.

"I took the dates of the swarms hitting power stations and checked the lunar schedule. I found they arrived when the moon was full, or almost full," Algazi says.

Correlation between nomadica jellyfish swarming and the lunar cycle (Hebrew calendar).Credit: University of Haifa, Avi Algazi

He then thought of two theories as to why the full moon might be correlated with nomadica swarming.

The moon's gravity is not strong enough to affect the water in our bodies, let alone in a jellyfish's. Nor did Algazi buy the thought that the effect was tidal – the tide rises and falls twice a day, he points out. "The trigger to the full moon's biological influence on the jellyfish seems to be its light," he concluded.

Like in coral, the full moon's light may trigger the sexual stage of jellyfish procreation. That is when the males spill their sperm into the shallows of the sea, the females release their eggs and together they make, not baby jellies exactly but polyps, he explains. Those polyps find places to settle down on the seabed, like on rocks and shipwrecks; each will asexually proliferate, splitting into clones, and each such clone, if it survives, turns into a jellyfish.

Life cycle of a jellyfishCredit: The Visual Dictionary

His data show clearly that jellies swarmed in Israel when the sea temperature was in that specific narrow range and when the moon was full, or nearly so. Using these data to reach reliable forecasts is another story.

"Prophecy is a harsh goddess," he laughs. "I cannot predict that jellyfish will arrive on a certain date or even in a given week. But I can speculate." In some years jellyfish hardly swarm at all, he points out. Clearly more study is needed, but his discovery is the first indication of correlations that can help predict swarming behavior by jellyfish.


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