The heat brings harefish and giant jellyfish to the Mediterranean

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Heat wave can bring dramatic changes to fauna and flora, causing ‘species migration’ to less warm waters

A “major marine heat wave” has been hitting the western Mediterranean since the end of May, with temperatures “particularly” hot, 4°C to 5°C above normal and threatening marine ecosystems, according to experts on climate change in the Mediterranean .

This major marine heat wave started at the end of May in the Ligurian Seabetween Italy and northern Corsica, and then in June continued into the Gulf of Taranto in southeastern Italy, the Carina von Schuckmanna German oceanographer at Mercator Océan International.

The non-profit organization based in Toulouse includes the main oceanographic institutes of France, Italy, Spain, Britain and Norway and leads the European ocean monitoring service, the Copernicus Marine Service (CMEMS).

On July, “from the Balearic Sea (Spain) to Sardinia (Italy), as well as east of Corsica and the whole of the Tyrrhenian Sea, extremely high temperature values ​​between 28°C and 30°C are observed on the surface, higher than normal, of the order of +4°C to +5°C”, according to Mercator Océan International.

If for the bathers in these seas, one of the main tourist destinations in the world, these temperatures are pleasant, for scientists and environmentalists they are a source of concern.

This sea heat wave can bring about dramatic changes in fauna and flora, causing “species migration” to less warm waters, mass mortality of species or the decline of some and the appearance of new species, warns Karina von Schuckmann who is also one of the editors of the reports. of the UN Intergovernmental Panel on Climate Change (IPCC, GIEC).

And all these changes will have socio-economic consequences, mainly in the fishing sector, he warns.

Harefish and giant jellyfish

In the Mediterranean, following oceanic heat events in 1999, 2003 and 2006, numerous cases of mass mortality of species such as posidonia were observed“, according to his report Center national de la recherche scientifique (CNRS) published in 2020.

For Charles-Francois BoudouresqueProfessor of Marine Ecology at the University of Aix-Marseille, the consequences of this “sea heat” are being studied, but predictions lead to “total or partial” mass die-offs of posidonia and red coral.

Fish such as the colorful barracuda, which have started to rise from the south to the north of the Mediterranean, are also at risk of increasing their populations in the western Mediterranean.

Species from the Red Sea that entered the eastern Mediterranean through the Suez Canal» are also approaching the French coast, and two of these species are likely to be a problem in five or ten years: the harefish and the giant Rhopilema jellyfish.

The harefish is an “extremely voracious herbivore” fish that “threatens to disrupt normal food chains.” Already present off Lebanon, its population growth in the western Mediterranean threatens the algal forests that provide nursery services for other fish.

The giant jellyfish causes serious stings that require hospitalization and cause the closure of beaches when its presence is detected, warns Charles-Francois Boudouresque.

“To deal with ocean heat, greenhouse gas emissions will have to be reduced, but even if we stopped emissions today, the oceans, which store 90% of the Earth system’s heat, would continue to warm,” he explains. Karina von Schuckmann.

These marine heat waves have already “doubled in frequency since the 1980s,” according to the UN Intergovernmental Panel on Climate Change’s August 2021 report.

Between 2015 and 2019, “the Mediterranean has experienced five consecutive years of mass species die-off” due to marine heat waves, an article in the scientific journal Global Change Biology (July 18) also points out.

At least since 2003, these waves have become systematic and in the future they will have a longer duration, occupy a larger area of ​​the sea and will be more intense and severe» putting a sea that is valuable in terms of biodiversity to a great test, warns Karina von Schuckmann.

Although the Mediterranean Sea covers less than 1% of the planet’s ocean surface, it is home to 18% of all known marine species and the largest proportion of marine ecosystems in Europe, highlighted in the report of the Mediterranean Climate Change Experts Network ( Medecc).

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