Israeli scientists explain why ‘tens of millions’ of jellyfish seen off coast

Marine biologists have explained why the Israeli coast has been hit by a far higher number of jellyfish than previous years.

University of Haifa scientists said swarms of “tens of millions” of jellyfish were being seen because exceptionally heavy rains this winter had washed extra nutrients into the Mediterranean Sea.

“High rainfall washed out large quantities of nutrients to our normally nutrient-poor sea, driving production rates up and providing lots of food to all members of the marine food web, including the jellyfish,” said Dr Tamar Lotan and Prof Dror Angel at University’s Leon H. Charney School of Marine Sciences.

Jellyfish swarms have been seen in Israel since the 1980s and the animal is now established along the coast, at one point “invading” a power station in southern Israel and now threatening to wipe out local fish life.

“The impacts of jellyfish to the ecosystem are numerous,” said Lotan and Angel. “They compete directly and quite efficiently with larval and young finfish over planktonic food, and can cause these fish populations to starve.”

Jellyfish are predators and massive swarms or blooms can cause ecosystems to become unbalanced. A bloom is also a “massive biomass” so when that material sinks and decomposes it can cause dead zones on the sea floor.

As well as causing problems for fishermen, they can also cause mechanical clogging of coastal power plants that use seawater to cool their turbines, as well as problems to desalination plants that use seawater to generate freshwater.

The scientists said a better understanding of these swarms, including their habits and directions, would lead to informed fishing which in turn would protect finfish stocks, in order for the finfish to out-compete the jellyfish.

“We cannot avoid swarms, natural phenomena, but we must do more research to understand the dynamics of the swarms better, in order to better predict these.

“Common knowledge assumes there is ongoing competition between finfish and jellyfish because they all rely on the same food. Overfishing often results in reduced finfish populations which may give the upper hand to their competitors, the jellyfish. If we maintain healthier populations of finfish, it may reduce jellyfish swarms.”