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Corals and climate change
Angelique Brathwaite, Coastal Zone Management Unit
C
orals are the proverbial ‘canaries in the coal mine’ with
respect to climate change, existing within very narrow
environmental confines and so responding to even rela-
tively small changes in the environment. Corals are restricted to
essentially warm and clean waters with temperatures between
18-36°C (but with an optimal range of 26-28°C), salinity
between 3.3-3.6 per cent, moderate wave energy, low nutrients
and low sediment loading.
While seemingly fragile, both in terms of their structure and inabil-
ity to exist under broad environmental parameters, coral reefs have
existed on this planet well before humans and have adjusted to suit
their changing environment in major ways over geological time.
Reefs have formed, even if in different assemblages since at least
37–24 million years ago.
1
In contrast, our present day coral reefs
have been existing for a mere 10,000 years and are distinctly differ-
ent from those that thrived during the Oligocene and the Pliocene
times.
With respect to our changing climate, there are four major areas
of concern for coral reefs, and the primarily Small Island Developing
States (SIDS) that they protect:
• Increased temperatures
• Ocean acidification
• Sea-level rise
• Increased intensity of storms and hurricanes.
These are all serious issues for small tropical islands espe-
cially since there is no realistic expectation that the major
producers of greenhouse gases will change their modus
operandi in the near future.
2
The predictions from the Intergovernmental Panel on
Climate Change (IPCC) with respect to these elements
are dire, and it is probable that we will continue to lose
the enormous benefits of our coral reef ecosystems,
such as protection from high energy waves, nutrition
from their flora and fauna, medicines, tourism revenues
and their stunning, natural beauty if they come to frui-
tion, without major coastal infrastructural works. Of
course, one would also hope that the major global emit-
ters of greenhouse gases would change their practices,
and reduce their emissions.
Increasing temperatures
Coral bleaching, which occurs when sea surface
temperatures exceed the normal summer maximum by
1°C or 2°C for at least four weeks
3
has already had a
catastrophic impact globally on coral reef ecosystems.
The phenomena occur when the coral animal is stressed
and expels its algal symbiont (zooxanthellae), which
also produces much of the nutritional requirements
the animal needs for growth. The IPCC reports that if
all factors remain as they are, the warming trend will
continue at a rate of about 0.1°C per decade, due to
the slow response time of the ocean. It has also been
suggested that as a result of increasing greenhouse gas
emissions, temperatures over the tropical oceans will be
2°C and 3°C higher than the 1990 baseline by the 2050s
and 2080s respectively.
4
In addition current projections
suggest that the situation will only get worse with a
prediction that bleaching could become an annual event
within the next 30-50 years, with the highest incidence
in the Caribbean.
5
All predictions will have dire consequences for corals as
most of them exist quite close to their upper thermal limits,
and are already displaying adverse reactions to the increase
in temperature. It is expected that coral bleaching will
continue and coral diseases will flourish, while the ranges
of many species will change and fisheries will be harmed.
Major bleaching events occurred in 1997-98, where 50
per cent of tropical corals were bleached and just about 16
per cent of the world’s coral reefs were destroyed. In 2005,
the bleaching affected primarily the Caribbean region. In
Barbados, 90 per cent of all coral were affected and mortal-
ity due to bleaching was estimated at around 20 per cent.
6
T
he
I
mpacts
and
I
mplications
of
C
limate
C
hange
and
V
ariability
Erosion along the west coast of Barbados, 2009
Image: Coastal Zone Management Unit