The heat waves of last summer have left wounds that, in some cases, may be irrecoverable on the seabed of large areas of the western Mediterranean, including the coast of Catalonia and the Balearic Islands.
“It is as if a forest fire had passed. Sponges, gorgonians, corals and many other species were burned by the high temperatures, have lost their color or have died, and it will be difficult for them to recover”, explains Joaquim Garrabou, researcher at the Institute of Marine Sciences (ICM-CSIC) and author of various studies on the effects of marine heat waves in the Mediterranean. Soft sponges or corals are examples of groups affected by abnormally warm waters in areas such as the Costa Brava.
In the case of the arborescent gorgonian, the damage is much more similar to that of a forest fire, precisely due to the fact that these colonies of polyps grow to form structures similar to tree branches, and now have a gray and decrepit.
"We are confirming that the high temperatures of last summer caused episodes of mass mortality, and the most worrying thing is that they have affected species that form habitats, which serve as shelter or food for many other species," explains Garrabou, co-author of an international study. published in the journal Global Change Biology in which the effects of heat waves between 2015 and 2019 were analyzed.
This type of phenomenon began to be studied in the western Mediterranean in 1999, "but now we are verifying that they are becoming more frequent and intense", and many species cannot bear it and are disappearing", indicates the researcher. In the Mediterranean, species affected by warming cannot move north in search of cooler waters.
The data compiled and analyzed by Josep Pascual in l'Estartit indicate that last summer a record temperature of 27ºC was reached in the waters of this point of the Costa Brava, with an anomaly of four degrees compared to the average of the last 30 years. In the Balearic Islands, five marine heat waves were recorded with a spectacular maximum of 31.36ºC at the buoy located in the waters of Dragonera Island, on August 24, according to Puertos del Estado. The Valencia buoy reached 29.94ºC on August 11; that of Tarragona reached 29.77ºC that same day; those of Cabo de Palos and Cabo de Gata reached 29.37ºC and 27.93ºC at the end of July and that of Ceuta had its historical maximum at the beginning of August with 24.6ºC.
The reports on sea surface temperature prepared by the Meteorology and Pollutant Dynamics group of the Center for Environmental Studies of the Mediterranean (CEAM, in Valencia) agree that "since the beginning of June" temperatures have been recorded in the western basin of the Mediterranean " well above the climatic average”, reaching an average of 27.4ºC in August.
“Climate change shows us that these heat waves in marine waters will continue to be repeated more and more, causing an irreparable loss of biological diversity”, concludes Joaquim Garrabou.
