Dozens of marine species in the Mediterranean Sea are changing their habitats, migrating dozens of meters deeper into cooler waters in order to survive, according to a study published Thursday by researchers at Tel Aviv University.
The analysis of 236 species found that fish, crustaceans, and mollusks, such as squid, were migrating an average of 55 meters (180 feet) deeper across the Mediterranean.
The pattern of moving into deeper waters was not uniform between all species, the researchers said.
Cold-water species were found to migrate deeper significantly more than warm-water species; species that live along a narrow depth range deepened less than species that live along a wide depth area; and species that are able to function within in a wider temperature range deepened more than those who can function only within a narrow temperature range.
The study — published in the journal Global Ecology and Biogeography — was led by TAU Ph.D. student Shahar Chaikin under the supervision of Prof. Jonathan Belmaker, and along with researchers Shahar Dubiner, from the School of Zoology in the George S. Wise Faculty of Life Sciences and the Steinhardt Museum of Natural History at Tel Aviv University.
According to the researchers, the entire planet has experienced warming on recent decades, but this process has been significantly more noticeable in the Mediterranean Sea. The average water temperature in the Mediterranean rises by one degree Celsius (33.8 degrees Fahrenheit) every thirty years, and the rate is only accelerating, the study said.
“It should be remembered that the Mediterranean was hot in the first place, and now we are reaching the limit of many species’ capacity,” explained Prof. Belmaker.
“Our research clearly shows that species do respond to climate change by changing their depth distribution,” Chaikin said, “and when we think about the future, decision-makers will have to prepare in advance for the deepening of species. For example, future marine nature reserves will need to be defined so that they can also provide shelter to species that have migrated to greater depths. And on the other hand, fishing in the future will involve fishing the same fish at greater depths, which means sailing further into the sea and burning more fuel.”
“Even if species deepen to escape the warm waters and this rapid adaptation helps them, there is still a limit — and that limit is the seabed,” added Prof. Belmaker. “We are already seeing deep-sea fish like cod whose numbers are declining, probably because they had nowhere deeper to go.”
Earlier this month, the World Meteorological Organization (WMO) said that the years from 2015 to 2021 are on track to be the seven hottest on record, warning that the planet was heading into “uncharted territory.”
The preliminary WMO state of the climate report, launched as the United Nations COP26 climate conference opened, said that global warming from greenhouse gas emissions threatens “far-reaching repercussions for current and future generations.”
The WMO found that the average temperature for 2021 was around 1.09 degrees Celsius (34 degrees Fahrenheit) higher than pre-industrial levels.
And the average temperature over the last 20 years (2002-2021), for the first time, exceeded the symbolic threshold of 1 degree Celsius above the mid-19th century, when humans began burning fossil fuels on an industrial scale.
The 2015 Paris Agreement saw countries agree to cap global warming at “well below” 2 degrees Celsius above pre-industrial levels, and 1.5 degrees Celsius if possible.
Since then the world has seen a litany of weather disasters, including record-shattering wildfires across Australia and Siberia, a once-in-a-thousand-years heatwave in North America, and extreme rainfall that caused massive flooding in Asia, Africa, the United States and Europe.