Climate crisis causes Mediterranean coral population to collapse

A new study, led by researchers from the Faculty of Biology and the Biodiversity Institute of Barcelona (IRBio), as well as the Institute of Marine Sciences of Barcelona (ICMSIC), found that marine heatwaves are causing coral populations to decline in the Mediterranean. The biomass of some corals has been reduced by 80-90 percent.

According to the study, published by the journal Proceedings of the Royal Society, coral populations of the Mediterranean —essential for the functioning of the coral reefs, one of the most emblematic habitats in this sea— could be unable to recover from the recurrent impact of these extreme episodes, with water temperatures reaching high degrees for days and even weeks.

This is the first study that assesses the long-term resilience of populations of two emblematic Mediterranean coral species, the red gorgonian and Corallium rubrum. These two species provide complex habitats which are essential for a large variety of associated fauna. It is important to understand how resilient they are to the more frequent and severe events. Extreme heatwaves.

Mass mortalities

The climate crisis is affecting the world in a severe way marine ecosystemsThe Mediterranean is no exception. Particularly, the sea heatwaves that are associated with the climate crisis are causing havoc in the Mediterranean. Mass mortalitiesIn all coastal ecosystems in this basin, the most affected species is the Mediterranean corals.

Despite the many studies that examined the immediate impact of the marine heatwaves upon corals, knowledge about the coral’s long term resilience is still limited. These corals are long-lived (some cases up to 100 years), and have slow population dynamics (organisms with low growth or recruitment rates). Therefore, researchers require long temporary series (decades), in order to assess their recovery potential.

The team also analysed the long-term monitoring results on coral populations affected by great mass mortality due to a Heatwave2003 in the protected marine region of Scandola, Corsega, France. They analyzed data regarding the state of these population (density structure, size, and biomass) collected by the MedRecover research group made up of experts from the UB and ICM–CSIC.

The results show that the 2003 heatwave caused all of the analyzed populations to plummet. These populations are now considered practically extinct from a functional perspective, fifteen years after the 2003 heatwave.

“We observed an average loss of biomass regarding the initial biomass of 80% for red gorgonians, and as high as 93% for the study population. Population of red coral,” notes Daniel Gómez, researcher at ICM-CSIC.

“These data are worryingly concerning for conservation of these emblematic animals and it indicates the effects of climate crisis are speeding-up with obvious consequences for submarine landscapes where the loss in coral equals that of trees in forest,” says Joaquim Garou, also member ICM-CSIC.

Recurrent heatwave exposure

Cristina Linares, professor at IRBio’s Department of Evolutionary Biology, Ecology and Environmental Sciences, and member of IRBio, states that “we believe one of our main reasons why we saw these collapse trajectories” is because of the potential recurrent heating waves, which are incompatible to the slow populational dynamics of these animals. In particular, during the study period (2003–2018), they registered important heatwaves in at least four years: 2009, 2016, 2017, 2018.

Linares says that during these heatwaves, the temperature conditions in the area reached extreme levels, which were incompatible for the corals’ life. This likely led to new mortality events and made it impossible for them to recover.

We anticipate the number and intensity of Heatwaves in the marine environmentMany coral populations could be at risk as temperatures rise in the coming decades.

“However, there may be areas in the Mediterranean where, due to a variety of factors, the likelihood of such climate impacts recurring again is lower. This makes it especially relevant to keep —regarding other potential impacts— these Climate“Refugees where the trajectories for coral populations could prove more positive than those observed here,” says the research team.

“But, there is a pressing need for stronger actions to be taken against the Climate crisis“Before the loss of biodiversity becomes irreplaceable,” concluded the experts.