Invasive jellyfish aren’t just drifting in chaos

Invasive jellyfish in Lebanon

Just as the weather heats up in the Mediterranean a nasty surprise makes it uncomfortable to surf and swim. After Egypt created the man-made Suez Canal to link the Red Sea to the Mediterranean Sea a nightmare of invasive animal, plant and bacterial species have overtook the Mediterranean Sea.

They compete with fish and habitat, causing harm to natural ecosystems. It’s been over 150 years since the canal was created and there is little evidence that Egypt has done anything to protect habitats on either side of the canal. Toxic jellyfish and invasive lionfish are two of the more well known invaders. Most worrisome has been the arrival of the Lagocephalus Sceleratus, an extremely poisonous bony fish commonly known as the silver-cheeked toadfish.

Desalination plants could create a salinity barrier that would slow the invaders from traveling back and forth but meanwhile research continues on the expansion and behavior of the newcomers.

The phenomenon of migrating from the Red to Med Sea is called the Lessepsian migration (or the Erythrean invasion). It is more rare for the migration to happen in the opposite direction.

One jellyfish, the invasive Rhopilema nomadica, is a nomad jellyfish indigenous to tropical warm waters of the Indian and Pacific Oceans. Since the 70’s it has been also found in Mediterranean Sea, where it entered via the Suez Canal. It is now the the commonest jellyfish in the southeastern Mediterranean, and they actually direct themselves and “swim” to the west while swimming, according to researchers who studied them.

“Until now, it was assumed that jellyfish aggregations swim in a random manner, so that their direction is dictated solely by water currents…We discovered that along the coast of Israel, jellyfish swim toward the west, i.e., against the direction of the waves,” said Dr. Yoav Lehahn of the Department of Marine Geosciences at the University of Haifa, the editor of the study.

Jellyfish belong to the phylum Cnidaria and have existed for around 500 million years without any morphological changes. Researchers’ knowledge about jellyfish is still very limited in many respects. One of the biggest unknowns  about jellyfish aggregations is the nature of their movement and migration patterns.

The lack of understanding of this aspect impairs the ability to prepare for the arrival of jellyfish at various facilities, such as power stations and desalination plants. “If the jellyfish were passive – in other words, if they were not able to move independently and simply drifted along in sea currents, we could predict the arrival of aggregations. We cannot do so, and this suggests that jellyfish have swimming capabilities that we do not yet understand,” the researchers explained.

The data collection stage in the study was complex: a light airplane flew along the coastline from Ashkelon in the south to Nahariya in the north, mapping the distribution of aggregations and identifying the largest ones. Next, the researchers monitored and photographed the direction of progress of the aggregations using drones operated from a nearby research boat.

The researchers examined the direction in which the aggregations swam relative to the sea currents and waves and found they swim collectively at a speed of around 10cm a second, moving to the west in a counter-wave direction. By so doing, they distance themselves from the coast and increase their chances of survival. The researchers added that the swimming patterns may vary between different jellyfish species and different maritime environments:

“When the strong tidal currents are dominant, it is possible that the jellyfish would swim against the current rather than against the waves, in order to reduce the risk of being swept onto the beach. In other cases, jellyfish may prefer to stay close to the coast, in inlets or estuaries. Swimming toward the open sea may not always be the first choice – the underlying objective is to reach a place where they have the best chances of survival.”

After storms, for example, large numbers of jellyfish are swept onto the beach, because they were unable to overcome the undertow created by the waves, the researchers note. The study advances our understanding of their movements, and in the future may allow us to predict when accumulations will arrive on coasts and when they will depart.

During the 2022 to 2023 fiscal year, the Suez Canal revenues hit a record-breaking $9.4 billion. Canal revenues are a key source of foreign currency for Egypt alongside tourism. Egypt should be earmarking a significant amount of these profits to helping protect the ecosystems that have been devastated. Why is no one holding Egypt accountable?

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