Jellyfish Finally Leave Israel’s Beaches, but There Was Something Unusual About This Summer's Swarm

Stinging cells they emit in the water make jellyfish showing up on the Mediterranean shores a threat to swimmers, in addition to clogging infrastructure outlets

A jellyfish at Achziv marine nature reserve, Israel, June 2019.
Shabi Rottman

The swarm of jellyfish that arrived to Israel’s beaches last month has finally moved on. What was special about this summer’s swarm was an increase in species not typical of the region – proof that additional species of jellyfish continue to enter the Mediterranean Sea through the Gulf of Suez and succeed in reproducing here.

The jellyfish that show up on Israel’s shores as a result of sea currents belong to a species called the nomad jellyfish. This species entered the Mediterranean decades ago through the Gulf of Suez from its natural breeding ground in the Red Sea and in tropical zones. The jellyfish are a threat to swimmers because of the stinging cells they emit into the water. They also clog infrastructure outlets. And when the swarm departs, it leaves many of its members dead on the sea floor.

A jellyfish on Tel Aviv's shores, June, 2019.
Tomer Appelbaum

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As the nomad jellyfish grew stronger, it pushed out barrel jellyfish, which is endemic to the Mediterranean. Scientists once thought that the barrel jellyfish would not allow other species to take root here because of its advantages in the competition for food. However, other species of jellyfish have indeed been seen arriving from the Gulf of Suez in recent years, albeit in small numbers. Among them are Phyllorhiza punctata, also known as the floating bell, as well as Marivagia stellata and Cotylorhiza erythraea. The latter were first collected on Israel’s beaches four years ago. These species also have stinger cells but they are considered less dangerous to humans.

Dead jellyfish on the Mediterranean Sea floor, Haifa Bay, Israel, July 2019.
Moti Mendelson

According to Bella Galil of the Steinhardt Museum of Natural History at Tel Aviv University, additional species of jellyfish appeared in much larger numbers this year. They were not as numerous as nomad jellyfish, but their numbers are growing. “This shows the great potential the Mediterranean Sea has for invasive species of jellyfish to reproduce. This process will probably continue, and there might be even more toxic species,” Galil said.

There are now more than 800 invasive species in the Mediterranean, and they have generated far-reaching changes in the ecosystem and expelled many local species. Jellyfish also prey on large numbers of young, local fish. It is believed that the climate crisis will make this situation worse since it will lead to conditions that make it easier for these species to strengthen their presence. Moreover, three years ago Egypt widened the Suez Canal, which means that more species can travel from the Red Sea to the Mediterranean.