New research: Some corals are adapting to heat stress from unusually warm seas
- 12 Mar 2012, 10:50
- Verity Payne
Certain species of coral reefs have been able to adapt or
acclimatise to heat stress from unusually warm seas, according to
study published in the open-access online journal PLoS
Corals live in partnership with algae that provide the coral
with food and give them their bright colours. When faced with long
periods of environmental stress like unusually warm seawater or
slight changes to ocean acidity, the algae are expelled from the
coral tissue, causing "coral bleaching".
It's possible for coral reefs to recover from bleaching, but
frequent, extensive and widespread bleaching can cause large
swathes of reef to die-off. This has led scientists to voice
concern over the future of coral reef systems, because of the
warmer seas and increased ocean acidification projected to
accompany man-made climate change over the coming century. There
have even been suggestions that as many as a
third of reef building corals face extinction.
research suggests that large, fast-growing reef-building corals
- Acropora corals - are particularly vulnerable to
coral-bleaching events, leading scientists to suggest that reef
ecosystems could see significant changes in the future with
Acropora corals are replaced by hardier varieties.
But this research looked at corals in three sites that
unexpectedly survived unusually warm seawater temperatures in 2010.
It found that in two cases in Singapore and Malaysia corals
survived a bleaching event in 2010, and had also survived a major
coral bleaching event in 1998. In the third site in Indonesia
however the Acropora corals responded typically, dying off
when faced with the unusual warmth of 2010. It turns out that the
Indonesian site did not experience a coral bleaching back in 1998.
So some coral reefs can withstand coral bleaching from warm
seawater if they've previously survived a similar bleaching.
The finding has surprised the scientists conducting the
research. Lead author Dr James Guest, joint research fellow at the
UNSW Centre for Marine Bio-innovation and Singapore's Nanyang
Technological University, writes in the paper:
"This suggests that the thermal history
of these sites may have played an important role in determining the
bleaching severity in 2010.[...] The most parsimonious explanation,
therefore, is that coral populations that bleached during the last
major warming event in 1998 have adapted and/or acclimatised to
thermal stress. This is controversial because many scientists
believe that corals have exhausted their capacity to adapt to
So how does this unexpected result fit with other pieces of
scientific research on the subject? It agrees with a previous
study which found that coral reefs that had been exposed to
frequent warming events were less likely to experience coral
bleaching. And this isn't the only way that coral communities can
adapt to climate change. Another study
suggests that corals might be migrating (slowly) in response to
climate change, a type of behaviour that has been also been
documented in the fossil record.
by-product of these adaptations is that new reef communities
become established, dominated by hardier corals, which alters the
coral reef ecosystem. The high population turnover associated with
the new communities established in mass bleaching events
can help enhance disease resistance.
The finding that some coral reefs might be able to adapt to
climate change is encouraging, but it isn't all good news. The
ability of coral to adapt to climate change relies on the climate
changing slowly enough to allow adaptation, and there are likely to
be limits to the seawater temperatures to which corals can adapt.
Scientists have warned that the heat stress of warmer seas and
ocean acidification resulting from man-made climate change might
interact with other threats - including pollution, overfishing and
disease - to make coral reefs more vulnerable in the future.
Still, as Guest writes in the paper:
"The results of the present study do
indicate, however, that the effects of coral bleaching will not be
as uniform as previously thought and fast-growing branching taxa
such as Acropora and Pocillopora are likely to
persist in some locations despite increases in the frequency of
thermal stress events."