Israel's annual jellyfish invasion and the full moon - what's the link?

University of Haifa researchers discover indicators to predict the arrival of the gelatinous masses to the waters off Israel's shores.

Jellyfish [File] (photo credit: INIMAGE)
Jellyfish [File]
(photo credit: INIMAGE)
The arrival of gelatinous masses of jellyfish at Israel’s shores is linked to the temperature of the Mediterranean Sea and the lunar cycle, say University of Haifa researchers.
The university’s department of natural resources and environmental management revealed, for the first time, that jellyfish arrive when the sea temperature ranges between 28.2 and 30 degrees Celsius and during the full moon.
“It is possible that individual jellyfish will also reach the coast during other conditions, but we discovered that the most significant swarms arrive under the above conditions.
The proof is that during such periods, the number of blockages of the cooling facilities of the Israel Electric Corporation due to jellyfish have been incomparably greater than during other periods of the year,” said Avi Algazi, who works in the corporation’s system management unit and who conducted the research.
Although jellyfish have become frequent unwelcome guests along the shores of Israel, researchers didn’t know for sure until now what factors cause the massive arrival of swarms in certain years while others have relatively few.
Algazi’s research showed that 94 percent of the arrival of jellyfish swarms occurred about 176 days from the beginning of the year, during the second and third weeks of the Hebrew month, which functions according the lunar calendar – when the moon ranges from between being almost full to full, and when sea water temperature ranges between 28.2 to 30 degrees Celsius.
Elgazi added that jellyfish also appeared when the moon was in other stages or when the sea temperature was different from that temperature range, but such occurrences were infrequent and were usually characterized by a small number of jellyfish.
The research also revealed that though the blockage of the cooling system filters led to only a small decline in the generation of electricity, they did constitute a significant part of the cooling system’s operational costs.
“The high cost is due to a number of factors; one is that the swarms arrive in June and July when demand for electricity is high... In addition, jellyfish – unlike other large objects that get sucked into the cooling system – are not controllable.”
Some block the moving filter after penetrating it and prevent seawater from being pumped in, causing the pump to shut down.