Jellyfish swarms offer new insights for coastal management

JERUSALEM – Shedding new light on the swarms of jellyfish that frequently reach the Israeli coast, researchers have discovered that jellyfish often actively swim against the direction of the waves.

Large swarms of jellyfish are known to disrupt power plants and desalination facilities by clogging intake pipes, impact fisheries and disrupt local marine ecosystems by preying on fish eggs and depleting oxygen.

Jellyfish stings can be painful, and sometimes dangerous to people, and swarms sometimes force the closure of beaches.

But new research, led by Dr. Yoav Lehn from the University of Haifa and recently published in the peer-reviewed Current Biology journal, will help marine biologists better predict the movement of jellyfish swarms.

"Until now, it was common to think that swarms of jellyfish swim randomly and that their movement in space is dictated solely by the currents of the sea," Lehn explained.

"But thanks to innovative research methods, we found that along the coasts of the country, the jellyfish swim towards the west, that is, against the direction of the waves."

Jellyfish, a member of the phylum Cnidaria, have existed for approximately 500 million years with little change in their morphology. Despite their long history, much about their behavior remains a mystery to scientists.

One of the most intriguing questions has been the migration patterns and movement routes of jellyfish swarms. Their unpredictability complicates preparations for their arrival, as traditional models based solely on ocean currents fail to account for the jellyfish's active swimming behavior.

The data collection phase was particularly complex, the researchers said.

Initially, a light aircraft flew along the Israeli coastline, from Ashkelon in the south to Nahariya in the north, to map the distribution of jellyfish swarms and locate large congregations.

In the next phase, drones operated from a research ship followed and photographed the swarms, providing detailed insights into their directional movement.

Finally, the researchers analyzed the swimming direction of the swarms in relation to sea currents and wave patterns.

"The use of a unique research method based on data collection from light aircraft, drones, and research ships allowed us to characterize the swimming and movement patterns of thousands of jellyfish and analyze them with the help of mathematical models," Lehn said.

The findings indicate that the wandering string jellyfish exhibit navigational abilities, swimming continuously towards the west at a speed of approximately 10 cm. per second.

By moving away from the shore and against the waves, these jellyfish increase their chances of survival.

However, the study also suggests that swimming patterns may vary between different jellyfish species and in different marine environments.

For instance, in areas with strong tidal currents, jellyfish might swim against the current rather than the waves to avoid being washed ashore.

In other environments, jellyfish might prefer to stay closer to shore, especially in sheltered bays or estuaries where conditions may favor their survival.

Despite their ability to swim against currents, jellyfish often end up near the shore, sometimes washing ashore and perishing.

According to the researchers, this is due to a combination of swimming and drifting.

In calm conditions with weak currents, jellyfish rely solely on their swimming abilities.

However, after storms or in strong currents, the drift can overpower their swimming, leading to their mass stranding on beaches.

"For example, after storms, many jellyfish reach the beach because swimming cannot overcome the drift created by the waves," Lehn explained. (PNA)