Sea temperature and the lunar cycle predict the arrival of jellyfish in Israel

Although Jellyfish s have become frequent guests along the shores of Israel -- as well as elsewhere throughout the world -- and despite their obvious and immediate impact on humans -- because swarms of Jellyfish can cause an abandoning of public beaches until they disappear -- until now researchers didn't know for sure what factors cause the massive arrival of swarms of Jellyfish s one summer while during another summer the quantity can be far less.

Algazi conducted the present study under the guidance of Prof. Abraham Haim -- Acting Head of the Leon H. Charney School of Marine Sciences and professor emeritus at the Department of Natural Resources and Environmental management, Dr. Keren Or-Chen of the Department of Natural Resources and Environmental management, and Dr. Anat Geffen Glazer from the IEC. For his study, Algazi sought to examine a link between the arrival of Jellyfish swarms, as determined by operational events that have occurred at the Eshkol Power Station in Ashdod, and environmental factors such as wind direction and speed, seawater temperature and the like.

The results showed that while the wind was not related to the appearance of giant swarms, 94% of the arrival of Jellyfish swarms occurred after the middle of the year (approximately 176 days from the beginning of the year), during the second and third weeks of the Hebrew month -- when the moon ranges between being almost full to full, and when sea water temperature ranges between 28.2 to 30.0 degrees Celsius.

According to Algazi, Jellyfish also appeared when the moon was in other stages, or when the sea temperature was different from range cited above. 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 Jellyfish swarms arrive during June and July when demand for electricity is high. Throughout those months, due to the high temperature of the sea -- both available pumps are operated in order to achieve maximum utilization of the production unit. In addition, Jellyfish s, unlike other large objects that get sucked into the cooling system, are not controllable; thus some block the moving filter after penetrating it, and prevent seawater from being pumped in. This causes the cooling pump to stop immediately," he explained.

The five power stations of the IEC located along the coast of the Mediterranean Sea use seawater to cool the steam condensers which turn gaseous steam back to liquid water for reuse in the production of electricity. The role of the condensers is very significant in the production of electricity, as is the continuous cooling of water. Cooling water originating in the sea held in a storage pool (an artificial pond connected to the sea through a narrow channel) which is protected by a breakwater and from there is pumped through the entrance channel to the condenser. Inside the entrance channel are three levels of filtration in order to prevent the penetration of foreign bodies into the condensers, which is where Jellyfish are also captured," concluded Algazi.