The climate crisis and the collapse of the Mediterranean coral
A new study led by teams from the Faculty of Biology, the Biodiversity Research Institute (IRBio) of the University of Barcelona and the Institute of Marine Sciences (ICM-CSIC) of Barcelona has revealed that marine heat waves associated with the climate crisis are reducing coral populations in the Mediterranean, whose biomass in some cases has been reduced by between 80 and 90%.
According to the study, published in the journal Proceedings of the Royal Society B, Mediterranean coral populations – essential for the functioning of coral reefs, one of the most emblematic habitats of this sea – may be unable to recover from the recurring impact of these extreme episodes, with water temperatures reaching high degrees for days and even weeks.
This is the first study to assess the long-term resilience of populations of two emblematic species of Mediterranean coral: the red gorgonian (Paramuricea clavata) and red coral (Red Corals), which provide complex habitats that are essential for a great diversity of associated fauna. Therefore, it is essential to understand their resilience in the face of more frequent and intense heat waves.
Mass mortality events
The climate crisis is seriously affecting marine ecosystems around the world, and the Mediterranean is no exception. In particular, marine heat waves associated with the climate crisis are causing mass mortality events in all the coastal ecosystems of this basin, and among the most affected species are Mediterranean corals.
Knowledge about the long-term resilience of coral is still scant, despite studies looking at the immediate impact of marine heat waves on these organisms. These are long-lived species (more than a hundred years in some cases) and slow population dynamics (that is, organisms with low growth and recruitment rates), so researchers need long time series (decades) to assess their ability to Recovery.
As part of the study, the team analyzed the results obtained in long-term monitoring of different coral populations affected by a large mass mortality caused by a heat wave in 2003 in the Scandola Marine Protected Area (Corsica, France). Specifically, they analyzed data on the status of these populations (density, size structure and biomass) collected during the fifteen years following the heat wave, by researchers from the MedRecover research group, made up of experts from the UB and the ICM -CSIC, among other centers.
far from recovery, the results show that all the analyzed populations tended to collapse since they were affected by the heat wave of 2003. Fifteen years after this event, these populations are considered virtually extinct from a functional perspective.
“We observed an average biomass loss with respect to the initial biomass of 80% in the red gorgonian populations, and of up to 93% with respect to the studied population of red coral”, says Daniel Gómez, researcher at the ICM-CSIC.
“These data are worrying for the conservation of these emblematic species, and indicate that the effects of the climate crisis are accelerating with obvious consequences for underwater landscapes, where the loss of coral is equivalent to the loss of trees in forests.”, points out Joaquim Garrabou, also a member of the ICM-CSIC.
Recurring exposure to heat waves
Cristina Linares, professor at the Department of Evolutionary Biology, Ecology and Environmental Sciences of the Faculty of Biology and member of IRBio, says that “We believe that one of the main reasons we observe these collapse trajectories is the potential recurrent exposure to heat waves, incompatible with the slow population dynamics of these species”. In particular, during the study period (2003-2018), they recorded significant heat waves in at least four years: 2009, 2016, 2017, 2018.
“During these heat waves”, continues Linares, “the temperature conditions in the study area reached extreme levels incompatible with the life of these corals, which probably caused new mortality events in the decimated populations and made recovery impossible”.
As we expect the number and intensity of marine heat waves to increase in the coming decades due to the climate crisis, the viability of many coral populations could be seriously threatened.
“However, there will probably be some areas of the Mediterranean where, due to various factors, the recurrence of such climate impacts may be less. This makes it especially relevant to maintain, in the face of other potential impacts, these climatic refugia where the trajectories of coral populations could be more positive than those observed in this study,” the research team points out. But nevertheless, there is an urgent need to implement stronger measures against the climate crisis before biodiversity loss becomes irreplaceable”, the experts conclude.
Population collapse of habitat-forming species in the Mediterranean: a long-term study of gorgonian populations affected by recurrent marine heatwaves.
D. Gómez-Gras, C. Linares, A. López-Sanz, R. Amate, JB Ledoux, N. Bensoussan, P. Drap, O. Bianchimani, C. Marschal, O. Torrents, F. Zuberer, E. Cebrian , N. Teixidó, M. Zabala, S. Kipson, DK Kersting, I. Montero-Serra,…. 22 December 2021. Royal Society