An “extraordinary” marine heatwave is sweeping the western Mediterranean with surface temperatures up to five degrees Celsius (41 degrees Fahrenheit) above average, according to experts contacted by AFP.
Although the record-breaking heatwave that hit northern Europe and the UK this month has subsided, experts said persistently hotter temperatures in the Mediterranean posed a threat to the entire marine ecosystem.
“This huge marine heatwave started in May in the Ligurian Sea” between Corsica and Italy, said Karina von Schuckmann, an oceanographer at the nonprofit research group Mercator Ocean International.
It then spread to the Gulf of Taranto in the Ionian Sea, she said.
By July, the heat wave had hit the Balearic Islands, Sardinia and the Tyrrhenian Sea.
“The map of the surface temperature anomaly shows higher than normal values of the order of +4 to +5°C from the east of the Balearic Islands to east of Corsica,” Mercator said in a statement.
While people may find the warmer water temperatures in the western Mediterranean’s tourist hotspots comfortable, the group warned that “warming of the ocean is affecting the entire ecosystem”.
“It is important to be aware of the possible consequences for local fauna and flora, as well as the occurrence of extreme weather events that can lead to natural disasters,” it said.
Von Schuckmann said unusually warm temperatures could lead to irreversible migrations for some species and “mass extinctions” for others.
She pointed to knock-on effects for industries like tourism and fishing that rely on favorable water conditions.
According to the UN Climate Science Panel, the frequency of marine heat waves has doubled worldwide since 1980.
– Die-off, invasive species –
Although the Mediterranean Sea accounts for only 1 percent of the Earth’s sea surface, it contains nearly 20 percent of all known marine species.
A study published this month in the journal Global Change Biology found that between 2015 and 2019 there had been five consecutive years of mass extinctions in the Mediterranean.
The French research center CNRS has found that heat waves at sea in 1999, 2003 and 2006 led to the mass extinction of some species, in particular the Posidonia, a genus of flowering plants.
“We can predict that the main impact will be on solid organisms such as plants or corals,” said Charles-Francois Boudouresque, a marine ecologist at the University of Aix-Marseille.
However, some fish species such as the barracuda could be more common in the warming waters of the northern Mediterranean.
Boudouresque said some species entering the Red Sea through the Suez Canal could become problematic “within five to 10 years”.
These include the rhopilema – a herbivorous jellyfish – and the rabbitfish, which Boudouresque described as “extremely greedy”.
Already abundant in the eastern Mediterranean, its presence in western waters would threaten the algal forests that nurture countless fish species.
Rhopilema can also sting swimmers severely enough to require hospital treatment.
Because there is little governments can do once an ocean heatwave hits, von Schuckmann said the best course of action is to reduce greenhouse gas emissions that contribute to warming.
“Even if we stopped emitting today, the oceans, which contain 90 percent of the Earth’s heat, will continue to warm,” she said.
“Since at least 2003 (marine heat waves) have become more frequent and will be longer in duration, cover more sea and be more intense and severe in the future,” von Schuckmann said.
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