Rising sea temperatures are causing marine species from the Mediterranean to spread into the Black Sea, experts warned in an Anadolu Agency (AA) report, potentially leading to a "Mediterraneanization" of the Black Sea and disrupting its ecological balance.

Data from the European Union's Copernicus Climate Change Service has revealed that the global average sea surface temperature reached a record high of 21.07 degrees Celsius (69.93 degrees Fahrenheit) in March. Furthermore, 94 out of the 100 warmest days on record for daily average sea surface temperatures occurred in 2024.

Similar increases in sea surface temperatures have been observed in waters surrounding Türkiye. In 2023, the average sea temperature in Turkish waters was higher than the long-term average.

For the Black Sea, the 1970-2023 average was 15.3 degrees Celsius compared to 16.8 degrees in 2023. In the Marmara Sea, the average rose from 15.7 degrees (1970-2023) to 17.6 in 2023. In the Aegean Sea, it increased from 18.7 degrees to 20.5, and in the Mediterranean, from 21.5 degrees to 22.6.

Professor Onur Gönülal noted that climate change and rising sea temperatures are causing significant alterations in marine ecosystems. Species suited to the Red Sea are spreading into the Mediterranean, Marmara and Black Seas, largely due to these changes.

Gönülal reported a rising number of invasive species each year, with a 2020 study identifying 539 foreign species in Türkiye. In the Black Sea, the number of invasive species is approaching 30, while in the Marmara, it has exceeded 100. The Aegean hosts 253, and the Eastern Mediterranean has 413 foreign species.

Gönülal warned that if this trend continues, the number of invasive species may surpass native species. He estimated that without the high temperatures, the number of foreign species would likely have remained around 100-150, suggesting that rising temperatures might have increased the spread of invasive species by five or six times their normal levels.

Economic losses

Gönülal emphasized that the spread of invasive species disrupts the ecological balance by competing with native species, which is a global issue, not just a problem for Türkiye. He noted, "There is a gradual trend of Mediterraneanization in the Black Sea, which is not limited to foreign species."

He further explained: "Rising temperatures reduce the temperature differences between the Mediterranean and Black Seas, allowing some species to spread. The Mediterranean and Black Sea ecosystems are different, but with increasing temperatures, fish species native to the Mediterranean and Aegean are starting to spread into the Marmara and Black Seas."

Gönülal highlighted that the rapid spread of foreign species in the Black Sea and surrounding regions is a significant issue, noting that high-value species such as the blue crab (Callinectes sapidus) and two types of jumbo shrimp (Penaeus aztecus and Penaeus pulchricaudatus) have been spreading rapidly in the Marmara and Black Seas.

He warned that these species competing with native species for resources could disrupt the ecological balance of the Black Sea.

Species at risk

Associate professor Cem Dalyan pointed out that rising sea temperatures are leading to the spread of Mediterranean fish such as the sea bream and the gilt-head bream into the Black Sea, and records of the fast-swimming mahi-mahi are appearing in the Marmara.

Dalyan noted that these fish are Atlant-Mediterranean species. "For example, the mahi-mahi is a strong pelagic predator that usually feeds on small fish. Pelagic species known in the Marmara include anchovies and sardines. The potential formation of large populations of mahi-mahi in the Marmara could exert pressure on pelagic fish and profoundly impact the migration phenomena between the Black Sea and North Aegean."

He emphasized that the introduction of a new species into an ecosystem alters the food chain, stating: "Species in the Black Sea, where much of our fishing occurs and which has developed over thousands of years, are under the threat of Mediterraneanization. Understanding their role in the food chain and their impact on the ecosystem is currently impossible due to a lack of data."

Dalyan concluded, "With the Mediterraneanization of the Black Sea, we may see fewer anchovies in markets, leading to economic and ecological changes."

He added: "The concept of 'Mediterraneanization' means that the flora and fauna of the Mediterranean dominate the Black Sea, leading to the loss of the Black Sea's unique characteristics. This could result in the disappearance of the biological differences between the two seas, loss of ecosystem diversity and the formation of a single ecosystem."

Dalyan warned that if ecosystems become homogenized, the negative impacts will spread throughout the region, risking the preservation of diversity and the values of different ecosystems.

He stressed the need to limit humanity's impact on nature, stating: "We have no other planet to go to. Pollution in our seas must be reduced, and efforts must be made to protect marine ecosystems. Overfishing, pollution and rising temperatures are making ecosystems unhealthy and leading to the extinction of sensitive species."

"Rapid habitat and coastline loss due to urbanization stress ecosystems and make it difficult for species to adapt. It is crucial to preserve the current ecosystem through measures such as regulating industrial fishing, supporting small-scale fisheries, reducing pollution pressure, creating marine protected areas and monitoring and controlling non-native species in the Black Sea."