Marine Heatwaves Devastate Red Gorgonians of the Medes Islands

One of the most evident effects of climate change is the increased frequency and intensity of marine heatwaves. A study led by the University of Barcelona, with participation from researchers at the Mediterranean Institute for Advanced Studies (IMEDEA, CSIC-UIB), has shown that the extreme heatwave of 2022 caused unprecedented mortality in populations of the red gorgonian (Paramuricea clavata), an emblematic soft coral species of the Mediterranean that plays a crucial role in the formation of coralligenous habitats.

According to the study, recently published in the Journal of Animal Ecology, the rise in temperatures affected 70% of the colonies located in the Montgrí, Medes Islands, and Baix Ter Natural Park. These alarming results threaten the viability of this species, which is of great importance for the biodiversity of benthic ecosystems.

Four Years with Temperatures Exceeding 24.3°C

The new study evaluated the impact of marine heatwaves that occurred between 2016 and 2022 on seven populations of Paramuricea clavata located in the protected area of the Medes Islands. The results reveal a significant increase in mortality rates (calculated from the accumulated proportion of affected colonies and the dead surface area) during the years when these events were most intense and prolonged: 2017, 2018, 2019, and 2022.

In these four years, temperatures exceeded 24.3°C, with 2022 being the year with the highest recorded mortality. "In 2022, the proportion of colonies affected by the 50-day heatwave was close to 70%, with a nearly 40% damaged surface area, unprecedented values since we began monitoring these populations," the authors explain.

This negative impact is also the cumulative result of previous events, as the recovery of these organisms is extremely slow.

Until now, the P. clavata populations in this small marine reserve had shown greater resistance to heatwaves compared to other populations in the Mediterranean. This resilience led researchers to consider them a possible climate refuge. However, in light of the study’s results, the future of Paramuricea clavata throughout the Mediterranean appears bleak, suggesting that the resilience of this species may not be enough to ensure its survival in the predicted warming scenario.

Photo: Colonies of red gorgonian (Paramuricea clavata) affected by the marine heatwave. The mortality caused by elevated temperatures is evident in the denuded skeleton of the colony on the right. Author: Eneko Aspillaga.

Moreover, these findings have implications beyond the survival of the species itself. Due to its structural complexity and role as a habitat-former, its disappearance could trigger severe deterioration in biodiversity and the functioning of coralligenous ecosystems, the most diverse marine habitat in the Mediterranean.

The situation is so critical that, even with the implementation of measures to mitigate all possible impacts in the protected area, scientists remain pessimistic about the species' recovery capacity.

The results obtained in the Medes Islands Marine Reserve not only highlight the importance of protecting these ecosystems but also provide a window into predicting the future of other marine ecosystems worldwide.

Reference:

Rovira, Graciel·la; Capdevila, Pol; Zentner, Yanis; Margarit, Núria; Ortega, Julia; Casals, David; Figuerola-Ferrando, Laura; Aspillaga, Eneko; Medrano, Alba; Pagès-Escolà, Marta; Hereu, Bernat; Garrabou,  Joaquim; Linares, Cristina

"When resilience is not enough: 2022 extreme marine heatwave threatens climatic refugia for a habitat-forming Mediterranean octocoral"

Link to the complete publication here