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Climate Change Is a Major Threat to Coral Populations
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Climate Change Is a Major Threat to Coral Populations

Mediterranean Coral Populations Gravely Affected by Climate Change.


A new study has shown that the marine heatwaves associated with the climate crisis are causing a decline of coral populations in the Mediterranean. In some cases, the biomass has fallen by 80-90%.

Mediterranean Coral Populations Gravely Affected by Climate Change.
Paramuriceaclavata, a healthy population, is found in the Scandola protected marine area. (Image Credit: Medrecover).

The Faculty of Biology and the Biodiversity Institute (IRBio), both comprise the research teams. University of BarcelonaThe Institute of Marine Sciences (ICM CSIC) of Barcelona.

According to the research, coral populations of the Mediterranean — vital for the functioning of the coral reefs, one of the most symbolic habitats in this sea — could be incapable of recovering from the repeated impact of these extreme climate episodes, with water temperatures soaring to high degrees for days and even weeks.

The journal has published details of the study. Proceedings of the Royal Society B.

This is the first study to assess the long-term recovery potential of populations of two symbolic species of Mediterranean coral: red coral ().Corallium rubrum) and the red gorgonian (Paramuricea clavataThese habitats are essential for a wide range of fauna. It is therefore crucial to understand their resilience to heatwaves that are more frequent and severe.

Mass mortalities

The climate crisis has severe consequences for marine ecosystems worldwide, including the Mediterranean. Particularly, the climate crisis is causing mass deaths in all coastal ecosystems. The most affected species of corals are the Mediterranean corals.

Awareness regarding the coral’s long-term resilience is still limited, despite the studies that investigated the direct effect of marine heatwaves on these organisms. These corals have a long life span (up to 100 years in some instances), but they also have slow population dynamics, which means that scientists need long temporary series (decades), to evaluate their recovery.

As part of their research, scientists examined long-term monitoring of coral populations that were affected by large mass mortality from a heatwave that struck France in 2003. This was in the secure marine area Scandola (Corsega).

Specifically, they explored data on the conditions of these populations (size structure, density and biomass) gathered during the 15 years after the heatwave, by the scientists of the MedRecover research group, formed by experts of the UB and ICM-CSIC, among other centers.

All of the examined populations collapsed as a result of the 2003 heatwave. These populations are now practically extinct functionally 15 years after the 2003 heatwave.

We observed an average loss of biomass of 80% in red gorgonian populations, and a maximum of 93% in red coral populations.

Daniel Gómez, Scientist, ICM-CSIC

“These data are worrying for the conservation of these emblematic species, and it indicates that the effects of the climate crisis are speeding up with obvious consequences for the submarine landscapes, where the loss of coral equals the loss of trees in forests,” Joaquim Garou, who is a member ICM–CSIC, observes.

Recurrent Heatwave Exposure

We believe that one of the main reasons we observed these collapse trajectories was the potential recurrent heatwave exposure, which is incompatible with the slow population dynamics of these species.

Cristina Linares, Professor, Department of Evolutionary Biology, Ecology and Environmental Sciences, Faculty of Biology, University of Barcelona

Cristina Linares is also a member of IRBio of University of Barcelona.

Particularly, during the years of the study (2003-2018), they noted critical heatwaves in at least four years: 2009, 2016, 2017 and 2018.

These heatwaves caused extreme temperature conditions in the area to reach levels that were incompatible with coral life. This likely resulted in new mortality events for the decimated population and made recovery difficult.

Cristina Linares, Professor, Department of Evolutionary Biology, Ecology and Environmental Sciences, Faculty of Biology, University of Barcelona

The climate crisis is expected to increase the intensity and frequency of heatwaves in the oceans over the next decades, which could mean that coral populations could be seriously endangered.

“However, there will probably be some areas in the Mediterranean in which, due to several factors, the recurrence of such climate impacts may be lower. This makes it especially relevant to keep — regarding other potential impacts — these climate refuges where the trajectories of coral populations could be more positive than those observed in this study”,The research team is observed.

“Nevertheless, there is an urgent need for stronger measures to be implemented against the climate crisis before the loss of biodiversity becomes irreplaceable”,The researchers concluded.

The research team acknowledges the support of the Regional Natural Park of Corsica, the HEATMED National Plan project (RTI2018-095346-B-485 I00), the European projects H2020, MERCES, H2020 Futurmares, Interreg MED MPA-Engage and Interreg MED MPA-Adapt.

Journal Reference:

Gómez-Gras, D., et al. (2021) The population collapse of Mediterranean habitat-forming species: A long-term study on gorgonians affected by recurrent heatwaves in the Mediterranean. Proceedings of the Royal Society.



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