Worries over fish and ecosystem as Mediterranean sea set to reach 30C

The Mediterranean Sea is heating up due to climate change, threatening its ecosystem, scientists have warned, with the water currently around 5C hotter than the seasonal norm.

Heatwave conditions in recent weeks saw the air in the Mediterranean area increase to 30C, and the sea to 27C, while on Monday (July 25) environmental journalist group AJE said that temperatures in the sea were set to hit 30C.

Divers in the area have observed more tropical fish species, and holidaymakers are enjoying the balmy conditions, as a result of the changes – but scientists warn that the rising temperatures are also threatening the ecosystem of the Med.

Diver Mickael Youssouf told France 3 that in 25 years, he has never seen so many fish in the area, including those seeking cooler temperatures at deeper depths, but also species normally only seen in the Red Sea, such as barracudas and triggerfish.

He said: “They are here in abnormal quantities. There are really more than usual, in an almost-tropical quantity.”

The number of heatwaves in the area has also more than doubled in the past 20 years, as the hot spells also grow longer and more intense.

Sandrine Ruitton, a specialist in marine biodiversity at the Institut Méditerranéen d'Océanologie, has warned that these changes could be causing lasting damage.

She told France 3: “The arrival of these exotic species can become invasive. These species can be voracious herbivores, and even carnivores that can replace and devour many fish, as well as invasive algae that can completely modify our ecosystems.”

The latter is especially dangerous, she said, as the algae can kill coral reefs and sea herbs, which are required to maintain the oxygenation of the sea and the marine ecosystem.

Similarly, Keraunos, the French observatory for tornados and violent storms, was alerted to the rising temperatures last week, and warned that “the thermal anomaly of the western Mediterranean is exceptional, and sometimes higher than 5C [above normal] off the coast of Provence”.

Robert Schlegel, a researcher at the Institut de la Mer in Villefranche, told the HuffPost: "With the exception of the Alboran Sea (between Morocco and Spain), the entire western Mediterranean has been experiencing a marine heat wave since around May 16.

“We are in a situation where, by 2050, most of the world’s oceans will be close to a state of near-constant marine heatwaves.”

Ecosystem changes globally

Carole Saout-Grit, a specialist oceanographer, added: “Between 1925 and 2016, the number of annual marine heatwave days in the world has risen by 50%.”

These figures come from a scientific paper published in the journal Nature Climate Change, in which researchers found a link between these heatwaves and long-term heating of the oceans.

This is likely to cause major ecosystem changes, the researcher added, and already, in 1999, 2003, and 2006, heatwaves in the Mediterranean caused “numerous cases of massive species mortality”, she said.

Elsewhere, new zones without oxygen have been found, including in the Pacific and Indian Oceans. These hypoxic areas are caused when the quantity of oxygen in the water is not enough to respond to the needs of the marine flora and fauna in the area.

Another sign of the changing oceans is the proliferation of jellyfish in the area. This is largely caused by a scarcity of fish, said Mélanie Ourgaud, an oceanographer, marine biologist and researcher at the CNRS.

She said: “There are not enough top predators (turtles, tuna, etc.) to eat jellyfish, and stocks of zooplankton eaters (sardines, anchovies, other small blue fish) that consume zooplankton (the same food resource as jellyfish) have been reduced.”

Heatwave and wildfires

Rising summer temperatures also increase the risk of wildfires on land.

La Direction Générale de la Sécurité Civile has yesterday (July 26) warned residents to be very careful due to the high risk of wildfires and drought in Occitanie, Provence, and Corsica following the recent heatwave.

The danger is increased by high winds, which can help blow blazes further out of control.

Dry ground and vegetation also create ideal conditions for fires. A total of 90 departments in France are now on alert for drought, since July 25, the Ecology Ministry confirmed.

Read more: Drought map update: See the French departments with water restrictions

This means that they are subject to water restrictions, with 11 departments on the highest alert level. Restrictions include a ban on watering gardens at certain times, or using water for farming.

Temperatures dropping

The recent heatwave has, however, now begun to abate across much of the country. Clouds are forecast, as is rain in the north, the Pyrenees, and in the northern Alps.

Temperatures are gradually dropping in many areas, with forecasts at between 18-22C in the Rhône-Alpes, and 23-24C from the Rhône valley to the Côte d'Azur. Elsewhere, they are set to drop to 12-18C.

The Mediterranean is still set to see high temperatures, however, at around 30-34C, and even 35-37C in the Languedoc and Var. It will be 20-25C on the Atlantic coast from Brittany to the Hauts-de-France, and around 25-30C in the rest of the country.

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