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Mediterranean Coral Populations Gravely Affected by Climate Change

A new study has discovered that marine heatwaves linked with the climate crisis are causing a decline in coral populations in the Mediterranean, the biomass of which in a few cases has decreased by 80-90%.

Mediterranean Coral Populations Gravely Affected by Climate Change.
A healthy population of Paramuricea clavata in the protected marine area of Scandola. (Image Credit: Medrecover).

The research teams belong to the Faculty of Biology, the Biodiversity Research Institute (IRBio) of the University of Barcelona and the 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.

Details of the study have been published in the journal Proceedings of the Royal Society B.

This is the first study to evaluate the long-term recovery capability of populations of two symbolic species of Mediterranean coral: the red coral (Corallium rubrum) and the red gorgonian (Paramuricea clavata), which provide intricate habitats that are vital for a huge diversity of related fauna. Therefore, it is important to understand their toughness concerning the more recurrent and extreme heatwaves.

Mass mortality events

The climate crisis is harshly impacting the marine ecosystems around the world, including the Mediterranean. Specifically, the marine heatwaves related to the climate crisis are resulting in mass mortality events in all the coastal ecosystems of this region, and among the most impacted species 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 are long-lived species (over a hundred years in certain cases) with sluggish populational dynamics (that is, organisms with low recruitment and growth rates), thus scientists need long temporary series (decades) to evaluate their recovery ability.

As part of the research, the scientists examined the results gained from long-term monitoring of different populations of coral impacted by huge mass mortality caused by a heatwave in 2003 in the secure marine area of Scandola (Corsega, France).

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.

The results exhibit that all the examined populations tended to collapse as they were impacted by the 2003 heatwave. Fifteen years following this event, these populations are virtually considered to be extinct from a functional viewpoint.

We observed an average biomass loss regarding the initial biomass of 80% in populations of red gorgonian, and up to a 93% regarding the studied population of red coral.

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,” observes Joaquim Garrabou, who is a member of ICM-CSIC.

Recurrent Exposure to Heatwaves

We believe one of the main reasons why we observed these collapse trajectories is the potential recurrent exposure to heatwaves, incompatible with the slow populational 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 the 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.

During these heatwaves, the temperature conditions in the studied area reached extreme levels which are incompatible with the life of these corals, which probably caused new mortality events to the decimated populations and made the recovery impossible.

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

Since the researchers expect the number and intensity of marine heatwaves to progress over the following decades because of the climate crisis, the sustainability of many coral populations could be grievously threatened.

“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”, observes the research team.

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

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) Population collapse of habitat-forming species in the Mediterranean: a long-term study of gorgonian populations affected by recurrent marine heatwaves. Proceedings of the Royal Society B.


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