A new study led by teams of the Faculty of Biology,
the Biodiversity Research Institute (IRBio) of the UB,
and the Institute of Marine Sciences (ICM-CSIC) of
Barcelona has revealed that marine heatwaves associated
with the climate crisis are bringing down the populations
of coral in the Mediterranean, the biomass of which in
some cases has been reduced by 80 to 90%.
According to the study, published in the journal
Proceedings of the Royal Society B, 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 to assess the long-term recovery
capacity of populations of two emblematic species of
Mediterranean coral: the red gorgonian (Paramuricea clavata)
and the red coral (Corallium rubrum), which provide complex
habitats that are essential for a great diversity of
associated fauna. Therefore, it is essential to understand
their resilience regarding the more frequent and intense
Mass mortality events
The climate crisis is severely affecting the marine ecosystems
worldwide, and the Mediterranean is no exception. In particular,
the marine heatwaves associated to the climate crisis are
causing mass mortality events in all the coastal ecosystems
of this basin, and among the most affected species are the
Figure.1 This image shows a colony of Paramuricea clavata which is partially dead due to the extreme heat conditions experienced during a marine heatwave. Photo: Eneko Aspillaga
Figure.2 A healthy population of Corallium rubrum in the protected marine area of Scandola. Photo: Medrecover
Knowledge on the coral’s long-term resilience is still
scarce, despite the studies that analysed the immediate
impact of marine heatwaves on these organisms. These are
long-lived species (more than a hundred years in some
cases) and with slow populational dynamics (that is,
organisms with low growth and recruitment rates), and
therefore researchers need long temporary series (decades)
to assess their recovery capacity.
As part of the study, the team analysed the results
obtained in a long-term monitoring on different populations
of coral affected by a great mass mortality caused by
a heatwave in 2003 in the protected marine area of
Scandola (Corsega, France). In particular, they analysed
data on the state of these populations (density, size
structure and biomass) collected during the following
fifteen years to the heatwave, by the researchers of
the MedRecover research group, formed by experts of
the UB and ICM-CSIC, among other centres.
Far from recovery, the results show that all the analysed
populations tended to collapse since they were affected
by the 2003 heatwave. Fifteen years after this event,
these populations are practically considered to be
extinct from a functional perspective.
“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”, notes Daniel Gómez, researcher at 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”,
notes Joaquim Garrabou, also member of ICM-CSIC.
Recurrent exposure to heatwaves
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 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”.
In particular, during the study period (2003-2018),
they registered important heatwaves in at least four
years: 2009, 2016, 2017, 2018.
Figure.3 A population of Corallium rubrum which has suffered a recent mass mortality event due to a marine heatwave. Photo: Olivier Bianchimani
“During these heatwaves”, continues Linares, “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
Since we expect the number and intensity of marine
heatwaves to increase over the following decades due
to the climate crisis, the viability of many coral
populations could be seriously 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”, notes 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 experts.
This study has been carried out thanks to 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.
UNIVERSITAT DE BARCELONA
Provided by the IKCEST Disaster Risk Reduction Knowledge Service System