Climate change accelerates vulnerability and loss of resilience of key coral species in the Med

A study by the University of Barcelona has analysed the ability of red gorgonians (Paramuricea clavata), a key species for the Mediterranean marine ecosystem, to resist and recover after marine heatwaves. The results, published in the Journal of Animal Ecology, show that the increased frequency and intensity of these extreme weather events — one of the consequences of climate change — will make these populations more vulnerable to future disturbances, beyond global warming and heatwaves, raising their risk of extinction. This negative impact would have a serious effect on marine ecosystems, according to experts.

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“Paramuricea clavata is a species that plays an essential role in a type of community endemic to the Mediterranean Sea, the coralligenous. These communities have a high associated diversity and represent approximately 10% of Mediterranean species. Therefore, a decrease in the resilience of these species, or even their extinction, can lead to major changes in the structure and functioning of the Mediterranean seabed,” warns Professor Pol Capdevila, from the Faculty of Biology and researcher at the UB’s Biodiversity Research Institute (IRBio), first author of the article. IRBio researchers Yanis Zentner, Graciela Rovira, Alba Medrano and Cristina Linares, together with Joaquim Garrabou, from the CSIC Institute of Marine Sciences, have also participated in the study.

Mediterranean sea has warmed faster than global oceans 

In the study, the researchers conducted long-term monitoring, from 1999 to 2022, of nine populations of red gorgonians located in the Montgrí, Medes Islands and Baix Ter Natural Park, and in the Port-Cros Natural Park, with the aim of finding out the resilience of these organisms to marine heatwaves.

“The Mediterranean Sea has warmed faster than the global oceans, making it one of the regions most affected by marine heatwaves, events that are expected to increase in frequency, intensity, duration and extent, even under the most optimistic climate change scenarios. Understanding the resilience of marine species to the increase in these extreme events is therefore crucial for predicting their viability under future climate conditions”, note the authors of the paper.

The study shows that P. clavata populations exposed to heatwaves have lower resilience and slower recovery rates than populations that have not been exposed to these events. “These results suggest that increased heatwave frequency is likely to accelerate the extinction of shallower populations of P. clavata. And not only that: what we have observed is that, after suffering a heatwave, these populations are less able to resist and recover from other types of disturbances”, Capdevila remarks.

This low resilience provides, according to the researchers, further evidence of the vulnerability of long-lived species to global change.

Similar effects in other areas of the Mediterranean

The researchers also suggest that this impact on P. clavata “is likely to be occurring in other Mediterranean locations as well”. For other coral species, the authors note that it is “likely that their resilience is also strongly affected by disturbance”, but they are more cautious. “It should be borne in mind that not all coral species have the same population dynamics. Paramuricea clavata is a species that is very dependent on the survival of its adult individuals, but this is not necessarily the case for other species. Therefore, our results are not necessarily extrapolable to coral species with faster population dynamics,” Capdevila adds.

The results contrast with the ecological memory hypothesis, i.e. the influence of past events on the current state of ecosystems. This hypothesis is based on studies conducted on the Great Barrier Reef, where it has been shown that the impact of heatwaves on corals can be lower if they have already been exposed to a heat wave the previous year.

“In the context of the Great Barrier Reef, the ecological memory hypothesis predicts that populations that have survived previous waves of disturbance may be less affected by new heatwaves. However, our results seem to indicate that, with more heat waves, the resilience of these species to further disturbances is lower,” says Pol Capdevila.

The researchers note that these differences may be since the mechanisms by which tropical and temperate corals achieve demographic resilience differ because of particular physiological and demographic characteristics.

Measures to minimize the impact on this species

Given these results, the experts propose measures to minimize the impacts on red gorgonian populations.

“For example, at the local level, populations of this species could be protected through marine protected areas or by restricting recreational activities, such as diving, where these corals are found. On the other hand, on a larger scale, measures to minimize climate change should be implemented more effectively, as it would benefit not only this species, but many others,” they conclude.