Marine heatwaves caused by climate change are driving threatening invasive fish and jellyfish to Greek waters, changing sea biodiversity.
Climate change is forcing fish from the Indian Ocean and the Pacific to migrate from warmer to cooler waters, such as those of the Mediterranean. They pass through the Suez Canal on their way west. These exotic varieties coming from eastern waters have been dubbed invasive fish, as their presence and behavior disrupt the Mediterranean marine ecosystem.
The bluespotted cornetfish (Fistularia commersonii), for instance, is considered one of the most destructive invasive fish in Greek waters and the Mediterranean in recent years. It feeds exclusively on the eggs of other fish. In short, in whatever marine environment it finds itself, it can turn the well-tuned underwater reproductive cycle upside down.
The cornetfish has been recorded in all Mediterranean sub-basins and has become very common in the eastern part. It is considered an invasive species in the Mediterranean Sea because of its rapid development in reproduction and its detrimental effect on native fish populations. Scientists agree that the cornetfish in the Mediterranean are all descended from a small number of ancestors.
Climate change and its rapid effects
Marine scientists attribute this underwater invasion to climate change. March 2024 was the warmest in history. It was 1.68 degrees Celsius (35 degrees Fahrenheit) warmer than the so-called pre-industrial times, meaning before humans started burning large amounts of fossil fuels, according to the EU Copernicus Climate Change Service.
What is more alarming is that March 2024 was the tenth month in a row marked by record-high temperatures.
Marine scientists warn that rising temperatures greatly affect the underwater world. One of the major problems it generates is the accelerating invasion of fish and other marine organisms, usually from the Red Sea through the Suez Canal into the Mediterranean. It is a phenomenon that is now on the rise, as we see that the normally cool waters of the Aegean Sea have become warmer.
The Lessepsian migration, as it is called, named in memory of the French diplomat, Ferdinand de Lesseps, who had undertaken the titanic task of opening the Suez Canal, is radically changing the Mediterranean biosystem.
Invasive fish in Greek waters
In the past two years, invasive fish from the Red Sea and the Indian Ocean have appeared in Greek waters. The most common of these are the lionfish and the silver-cheeked toadfish, both of which are venomous and pose a danger to other fish as well as humans.
The lionfish is a species of ray-finned fish native to the region of the western Indo-Pacific. It is a dangerous predator, competing for food and space with native stocks such as the snapper and grouper. According to scientists, the lionfish will also kill off helpful species such as algae-eating parrotfish, allowing seaweed to overtake the reefs.
These predators can grow up to 35 centimeters (14 inches) in length and have venomous fins. The dorsal fin has thirteen long, stiff spines and nine to eleven soft rays, and the anal fin has three long spines and six to seven soft rays.
Toadfish are named so because they look like toads. They belong to the Batrachoididae family, meaning “frog-shaped” in Greek. They are also extremely poisonous if consumed because they contain tetrodotoxin in their ovaries, and, to a lesser extent, in their skin, muscles, and liver. This substance serves to protect the species from voracious predators. Experiments have shown that the mating call of the toadfish alerts dolphin predators to the fish’s location.
The silver-cheeked toadfish, the Lagocephalus sceleratus (lagocephalus means having the head of a hare in Greek), appeared in Greek waters in the last two years.
Health hazard
The Tetraodontidae is a family of fish that includes species variously called pufferfish, blowfish, bubblefish, and so on. Most of these fish are toxic and dangerous to eat even though some of the species are considered a rare and pricey delicacy in Japan and China.
Since they are slow swimmers, blowfish are vulnerable to predators. To escape, pufferfish use their highly elastic stomachs and ability to quickly ingest huge amounts of water to turn themselves into a virtually inedible ball several times their normal size. Some species also have spines on their skin to make them even less palatable.
Consumption of such fish can cause paralysis of the muscular system or heart and respiratory failure that may even lead to death. In addition, blowfish can be aggressive as well. On the islands of Crete and Kalymnos, there have been recorded cases of people who ended up in the surgery room, as they encountered such invasive species while swimming. In addition to the health hazards their presence entails, they also cause great damage to fishermen’s nets.
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