Press
The heat in southern Europe is setting a new record: almost 30 degrees Celsius have been measured in the water in the Croatian Adriatic. This has drastic consequences, and not just for people.
Dubrovnik – The entire Mediterranean region is currently groaning under a heat wave, while in Central Europe an on-off summer is straining people’s nerves. The Balkan peninsula in particular is affected by temperatures of up to 40 degrees in Greece. Croatia is also battling an endless heat wave. The sea is also heating up like never before: On Monday (July 15) a new record for sea temperatures was recorded off the historic city of Dubrovnik in the south of the country.
The State Meteorological Institute (DHMZ) measured a sea temperature of 29.7 degrees Celsius at 5 p.m. This beat the previous Croatian record of 29.5 degrees in the sea near the island of Rab from 2015. In the rest of Croatia, too, a swim in the sea brought little refreshment: nowhere did the sea temperature fall below 26 degrees.
Nowhere in Croatia is the water cooler than 26 degrees
The 30-degree mark has already been broken off the Mediterranean coast of Turkey. Water temperatures of this kind were measured in Italy between Sicily and Naples last year, four degrees above normal. The sea was warm enough to swim in until November, and the summer season began in February this year.
The reason for high water temperatures is not surprising: “The main cause of the increase in marine heat waves is undoubtedly the global Climate changewhich leads to warming of the oceans,” said Katrin Schroeder, oceanographer at the Italian Marine Research Institute (ISMAR) to the German Wave.
Oxygen is becoming scarce for many living creatures – but the algae are blooming
The problem: Fewer gases such as oxygen and carbon dioxide can dissolve in warmer water. If oxygen becomes scarce, it becomes more difficult for many marine organisms to breathe. “In warmer water in particular, they actually have to breathe more because the higher temperatures speed up their metabolism,” Diego Kersting from the Spanish National Research Council (CSIC) explained to the broadcaster. But this is becoming increasingly difficult due to the lower oxygen concentration in the water.
Many sea creatures are also threatened with starvation due to the higher temperatures. “The increase in temperature accelerates the metabolism, and the organisms need more food to maintain this metabolic rate,” said Kersting. In addition, high temperatures often lead to a bloom of microalgae, which can release toxins into the air. The algal slime is currently also deterring holidaymakers from swimming in the upper Adriatic off Slovenia, Croatia and Italy.
![Bathers on the beach in Lerici in early January.](https://www.merkur.de/assets/images/33/745/33745419-badegaeste-am-strand-von-lerici-anfang-januar-2tzpvd53eLBG.jpg)
Many species of coral, mussels, starfish, sea urchins, sponges and sea grasses are suffering from the warm water. They cannot simply migrate to cooler areas like fish can. “We had very complex ecosystems that housed a high level of biodiversity and now we are losing them, at least in the shallow waters,” said Joaquim Garrabou, senior scientist at the Institute for Marine Sciences (ICM) of the CSIC in California (USA) to the German WaveAs early as 2022, a mass extinction of soil organisms was observed along thousands of kilometers of coastline
Jellyfish and poisonous exotic fish benefit from the warm Mediterranean
Jellyfish, on the other hand, are the ones that benefit from ocean warming. They can cope with the warm water and also benefit from nutrients that enter the oceans via sewage systems and agriculture, while at the same time fish are becoming fewer predators.
![The tropical, invasive lionfish is spreading in the Mediterranean.](https://www.merkur.de/assets/images/35/109/35109042-der-tropische-eingeschleppte-rotfeuerfisch-macht-sich-im-mittelmeer-breit-24qlDKu7F1BG.jpg)
Instead of native fish, exotic species are spreading: Introduced tropical species such as lionfish or puffer fish have already been sighted in the Adriatic, the Ocean and Fisheries Institute in Split reports to the National Geographic MagazineThe lionfish, which migrated from the Indian Ocean via the Red Sea and the Suez Canal, has poison in its ray fins that is very painful for humans. The poisonous harehead pufferfish, which also migrated from the Red Sea, has been causing major problems for Turkish fishermen for years. The pufferfish eats the fishermen’s shrimps, octopuses, other fish and crabs.
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