Mediterranean corals are ‘functionally disappearing’ due to climate change

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Climate change is affecting corals everywhere, including in the Mediterranean, according to a new study.

Paramuricea clavata. Image via Wikimedia.

Coral populations in the Mediterranean are suffering immense damage due to heat waves induced by climate change. Two emblematic species, the red gorgonian (Paramuricea clavata) and red coral (Corallium red), have lost 80-90% of their total biomass since 2003, according to new research.

The findings are very concerning. Coral populations are the backbone of the marine ecosystems to which they belong, providing food and shelter for a multitude of other species. The incredible decline observed in this article is probably indicative of the wider coral communities in the Mediterranean. If so, marine wildlife could be in a much worse situation than previously believed.

A sea of ​​trouble

“We observed an average loss of biomass compared to the initial biomass of 80% in the populations of red gorgonians, and up to 93% compared to the studied population of red coral”, notes Daniel Gómez, researcher at the Barcelona Institute of Marine Sciences (ICM-CSIC) and lead author of the study.

“These data are worrying for the conservation of these iconic species, and they indicate that the effects of the climate crisis are accelerating with obvious consequences for underwater landscapes, where the loss of coral equals the loss of trees in forests”, notes Joaquim. Garrabou, also a member of the ICM-CSIC.

The authors explain that populations of the two coral species studied may be unable to recover under current conditions. Their fate is due to rising temperatures, but above all to major heat waves that have hit the region on several occasions, the first occurring in 2003.

Water temperatures reach completely unbearable levels for these corals and maintain these temperatures for days or even weeks, the authors explain. As corals around the world are affected, this is the first study to quantify the effects of climate change and heat waves on Mediterranean corals specifically. Here, as in other regions, climate change is causing massive mortality in the coastal ecosystems of the sea.

These two species are emblematic of the Mediterranean and underpin the region’s complex ecosystems. They also have an important role to play in shaping the distinctive landscapes and appearance of the sea.

Researchers currently have information on the short-term response of corals to marine heat waves. That being said, corals are long-lived creatures with very slow population dynamics – they are slow to grow and spawn new generations) – so precisely understanding their response to climate change has taken decades of research. ‘studies. And that’s what the team did.

They used data from a long-term project by the research group MedRecover, which tracked different coral populations in the Scandola Marine Protected Area (in Corsega, France) which experienced mass mortality after the 2003 heat wave. Population density, size structure, and total biomass were of particular interest, as they were used as proxies for estimating the overall health of these coral communities. The data was collected for fifteen years after the heat wave (until 2018).

The data showed that not all populations monitored in the study recovered after the heat wave. In fact, they tended to crumble. Today, they are functionally extinct, the team explains.

“We believe that one of the main reasons we have observed these collapse trajectories is the potential recurrent exposure to heat waves. [in 2009, 2016, 2017, 2018], incompatible with the slow population dynamics of these species”, explains Cristina Linares, professor in the Department of Evolutionary Biology, Ecology and Environmental Sciences of the Faculty of Biology and member of IRBio, co-author of the article.

“During these heat waves, temperature conditions in the study area reached extreme levels incompatible with the life of these corals, which likely caused further mortality events to decimated populations and made recovery impossible.”

These populations are at serious risk of actual extinction, especially as the number and intensity of marine heat waves are expected to increase in the future as the climate crisis deepens. However, the team adds that there are likely areas in the Mediterranean where climate change impacts may be lower due to local factors. These should act as “climate refuges” to help preserve the corals, they conclude.

The team “Collapse of populations of habitat-forming species in the Mediterranean: a long-term study of gorgonian populations affected by recurrent sea heat waves” has been published in the journal Proceedings of the Royal Society B: Biological Sciences.

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