Some coral colonies
considered lost years ago,
show some living parts.
Some corals
can recover
after massive
mortality episodes
caused by a water
temperature rise.
This survival mechanism,
called "rejuvenation",
had only been described
previously in some
very old fossil corals.
A new study published
in the journal Science
Advances reveals
the first scientific evidence
of the rejuvenation
phenomenon in vivo,
in Cladocora caespitosa
coral colonies,
in the marine reserve
in Columbrets, on the
coast of Castellón (Spain).
Authors Diego Kersting and
Cristina Linares are from the
Department of Evolutionary
Biology, Ecology and
Environmental Sciences
from the Faculty of Biology
and the Biodiversity Research
Institute (IRBio) of the
University of Barcelona.
The Mediterranean Sea
has been one of the
most affected areas
by the climate change
and the increase
of heat waves.
“We are used to
hear and read on
the general impacts
related to climate change,
but we rarely get news
on the life recovery
after impacts related
to global warming”,
says Diego Kersting,
first author of the article.
Since 2002,
Kersting and Linares
have been monitoring
250 coral colonies
of Cladocora caespitosa
in the marine reserve
in Columbrets.
This coral is the only one
able to create reefs
in the Mediterranean Sea,
and is listed as an
endangered species,
mainly because of the
mortalities associated
with global warming.
The unusual rise
of water temperature
in the summer
was killing
many of these
Mediterranean
coral colonies.
During the
hot summer
of 2003,
“the 25% of the surface
occupied by these corals
in Columbrets disappeared
due a loss of the colonies”,
say the authors
of the study.
Some coral polyps
can survive under
extreme conditions
In a Mediterranean Sea,
the long-run monitoring
of the coral in Columbrets
revealed a surprising result:
Some coral colonies
considered lost years ago,
show some living parts.
This kind of recuperation
was possible thanks to
a procedure named
"rejuvenation".
Under stress conditions,
such as excessive water
warming, some polyps
in coral colonies,
which are dying,
are able to become smaller
until they can abandon
their calcareous skeleton.
In this reduced state,
these polyps can survive
under extreme conditions,
which cause the death
of the other polyps
in the colony.
When temperature
conditions improve,
polyps recover
their former size
and form a new
calcareous skeleton.
Then they reproduce,
by budding, until
they can recover
the dead colony again.
The authors claim
this survival strategy
had been unnoticed
due the external
good appearance
the colonies show,
after they have recovered,
which masks the mortality
that had taken place before.
“The real story
of these colonies
can only be found
if controlled every year,
over the years,
or if we study
the skeleton,
since the process
leaves characteristic
features!", say
Kersting and Linares.
So far, researchers
had found signs
of this rejuvenation
only in Paleozoic corals,
which lived hundreds
of millions of years ago.
This discovery provides
new perspectives
for the survival
of the only reef coral
in the Mediterranean,
which has a slow growth
-about 3 mm per year-
and a limited ability
to create new colonies.
"However, it is hard
for these mechanisms
to balance the
serious increase
of the frequency
and severity
of the heat waves
in the Mediterranean ... ",
warn the authors.