A study by the University of Barcelona has analyzed the ability of red gorgonians (Paramuricea clavata), a key species for the Mediterranean maritime ecosystem, to resist and recover after marine heat waves. The results, published in the Journal of Animal Ecology, show that the increase in the frequency and intensity of these extreme climate events – one of the consequences of climate change – will make these populations more vulnerable to future disturbances, beyond the global warming and heat waves, which increases their risk of extinction. This negative impact would have, according to experts, a serious effect on marine ecosystems.
«Paramuricea clavata is a species that plays an essential role in a type of community endemic to the Mediterranean Sea, the coralline. These communities have a high associated diversity and represent approximately 10% of Mediterranean species. Therefore, the decrease in the resilience of these species, or even 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 Institute of Biodiversity Research of the UB (IRBio), first author of the article. IRBio researchers Yanis Zentner, Graciela Rovira, Alba Medrano and Cristina Linares have also participated in the research, along with Joaquim Garrabou, from the Institute of Marine Sciences of the CSIC.
In the study, the researchers have carried out long-term monitoring, from 1999 to 2022, of nine populations of red gorgonian located in the Montgrí Natural Park, the Medes Islands and the Baix Ter, and in the Port-Cros Natural Park , with the aim of finding out the resilience of these organisms to marine heat waves. «The Mediterranean Sea has warmed faster than the global oceans, causing it to be one of the regions most affected by marine heat waves, events that are expected to increase in frequency, intensity, duration and extent; even in the most optimistic climate change scenarios. Therefore, understanding the resilience of marine species in the face of the increase in these extreme events is crucial to predict their viability in future climate conditions,” explain the authors of the article.
The study shows that P. clavata populations exposed to heat waves have less resistance and slower recovery rates than populations that have not been exposed to these events. ‘These results suggest that increasing the frequency of heat waves is very likely to accelerate the extinction of shallower populations of P. clavata. And not only that: what we have observed is that, after suffering a heat wave, these populations have less capacity to resist and recover from other types of disturbances,” highlights Capdevila.
This low resilience provides, according to the researchers, more evidence of the vulnerability of long-lived species to global change.
Effects on other areas of the Mediterranean
The researchers also suggest that this impact on P. clavata “is surely also occurring in other locations in the Mediterranean.” Regarding other coral species, the authors point out that it is “likely that their resilience is also greatly affected by disturbances”, but they are more cautious. «It must be taken into account that not all coral species have the same population dynamics. In the case of Paramuricea clavata it is a species that depends greatly on the survival of its adult individuals, but this is not necessarily the case in other species. Therefore, our results cannot necessarily be extrapolated to coral species with faster population dynamics,” adds Capdevila.
In this sense, the results contrast with the hypothesis of ecological memory, that is, the influence of past events on the current state of ecosystems. This hypothesis has been raised from studies carried out in the Great Barrier Reef, where it has been seen that the impact of heat waves on corals may be lower if they had 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 disturbances could be less affected by new heat waves. However, our results seem to indicate that, with more heat waves, the resilience of these species to other disturbances is lower,” explains Pol Capdevila.
The researchers highlight that these differences could be due to the fact that the mechanisms through which tropical and temperate corals achieve demographic resilience differ due to particular physiological and demographic characteristics.
Measures to minimize the impact
Given these results, experts propose measures to minimize the impacts received by red gorgonian populations. «For example, at a local scale, 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 large scale, measures should be implemented to minimize climate change more effectively, since it would not only benefit this species, but many others,” they conclude.
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