Home' Trinidad and Tobago Guardian : March 22nd 2017 Contents tobagotoday.co.tt March 22 - 2017
Faded brilliance--the loss of corals to disease
On my first dive in Tobago a
few years ago, I was stunned by
the beauty of the coral reef; the
colours of the stony corals and
sponges, the gorgonians swish-
ing with the waves and the mul-
titude of playful fish careening
After the dive, I was happily
chatted away by the older divers
who matter-of-factly told me
that the reef I had seen that day
was nothing compared to what it was like a
few years before. Back then I was told, the
reefs were covered in twice as much coral.
So what happened to our coral reefs? Well
a few things happened, some local while
others were global.
Forty years ago, Tobago's reefs looked much
different from how they do today. The coral
cover of stony "reef building" corals was far
more extensive, so much so that stony cor-
als dominated the reef floor over all other
reef organisms like soft corals, sponges and
In many reef areas along the leeward coast,
the most abundant of these stony corals was
the highly branched Acropora species, com-
monly known as Staghorn and Elkhorn cor-
als.These complex structures were exception-
al at providing numerous habitats for fish
and other reef creatures. There was also a
greater variety of stony coral species. But in
recent years, stony coral cover has fallen
dramatically to the point that on certain
reefs on the northern end of the island, stony
corals are no longer the primary organism
on the reef and have been replaced by spong-
es or soft corals which are less capable of
supporting the abundance of marine life that
stony corals can.
The previously abundant Acropora have
been reduced to a few scattered colonies
around Tobago, and replaced by simple
mound forming stony corals. In addition,
more and more coral colonies are being
observed with diseases.
The changes in the reef scape
have been brought about by both
chronic and acute stressor events
working in tandem over the years.
Climate change has for some
time been the greatest threat to
reefs since corals are particularly
vulnerable to its effects. Sea surface
temperatures rise [driven by climate
change] during the year to tem-
peratures high enough to cause
corals to undergo thermal bleach-
Corals exist in a symbiotic relationship
with microscopic algae called zooxanthellae
and gain most of their nutrients from the
zooxanthellae living within their tissues.
When corals become sufficiently stressed
they will expel their zooxanthellae, losing
their colour and resulting in a pale "bleached"
look. If corals remain without their zooxan-
thellae for extended periods of time, they
These periods of high sea temperatures
and the resultant bleaching episodes have
begun to increase in frequency and now
occur every few years. One such episode
occurred in 2010 which resulted in the death
of up to 50 per cent of stony corals on reefs
along the leeward coast of Tobago.
Stony corals grow very slowly and many
of the affected reefs have not yet regrown
the corals lost in 2010.
An additional effect of thermal bleaching
is the onset of coral diseases whose infection
rates typically explode a few months to a
year following a thermal bleaching event.
Coral diseases are becoming increasingly
important, especially in the Caribbean, in
shaping the reefscape as they are capable of
killing whole coral colonies and have been
known to wipe-out thriving coral populations.
Acropora, which once reached 46 per cent
cover in Buccoo's shallow reefs are now
gloomily non-existent. This unprecedented
loss is primarily attributed to a coral disease
called White-band disease.
White-band disease in not the only dead-
ly disease plaguing Caribbean corals. The
Caribbean region is known to have the great-
est variety of coral diseases with almost twice
as many coral diseases described in the
Caribbean than any other region.
Often the infectious agent is unknown but
we do know that there are human pathogens
capable of causing coral diseases.
Many of the coral species around Tobago
are vulnerable to multiple disease, and they
are being observed with increased frequen-
cy throughout the year. Of current concern
is the effect of Yellow-band disease on the
Star coral, Orbicella faveolata, which is cur-
rently the most abundant species in Tobago.
Some Star coral colonies appear not to be
vulnerable to Yellow-band disease. Since these
colonies may house different species of zoo-
xanthellae, the Institute of Marine Affairs (IMA)
is starting research to investigate whether there
exists a genetic susceptibility of either this
coral species or a specific zooxanthellae strain
to Yellow-band disease.
Sedimentation and nutrient pollution have
also been changing the reefscape. Sedimen-
tation can stress and kill coral and it reduc-
es diversity in affected areas to species that
are resistant while chronic nutrient pollution
retards colony growth, deforms coral recruits
[baby corals] and is known to worsen coral
Many of our reefs - which support our
fishing and tourism industries and protect
nearly 90 km of Tobago's coastline and
beaches from erosion - are struggling with
climate change, coral diseases and pollution.
The reefscape is changing.
It is becoming smaller and less bright but
there is still a window of opportunity to
reduce local stresses and give our reefs a
fighting chance against the effects of climate
change and coral diseases.
Biodiversity and Ecology Research Programme
Institute of Marine Affairs
Diseased Elkhorn coral. PHOTO: sero.nmfs.noaa.gov
The Caribbean can boast of a unique coral reef
biota. It is said to have occurred because of the
closure of the Isthmus of Panama some 3-4 mil-
lion years ago as well as its relationship with the
Although there is this longstanding boast of the
Caribbean's coral reef diversity it is not as rich as
the reefs in the Indo-Pacific. Still, there is much
to be thankful for as it said to be far richer than
of any other marine habitat type in the entire
Caribbean reefs have approximately 65 species
of hard corals and perhaps 500-700 reef-associ-
ated fish species.
Most of the reefs centre around the west-central
Caribbean Sea near to Jamaica and the Belize Bar-
rier Reef. The level of biodiversity in any reef depends
on its distance from that area.
The Bahamas is known to have 40-50 species
of stony corals but 62 species were recorded at a
single reef complex in Jamaica. In Jamaica, the
health of the reef was way above what prevailed
in similar reefs, particular Tobago's Buccoo Reef.
Similarly, in the Bahamas, the number of reef-as-
sociated fish species is "only" about 480, less than
80 per cent of the total reef fish species recorded
in the entire Greater Caribbean.
Chief Secretary Kelvin Charles, right, presents a cheque for $17,000 to Donna Petit-Walker, left and Dr Paula Henry, who are
directors of the HAIT&T Foundation directors, at the Office of the Chief Secretary at the Calder Hall Administrative Complex on
March 14. The Foundation is on a fundraising drive to assist in rebuilding infrastructure in Haiti which was damaged by earthquake
in 2010. PHOTO AND INFORMATION COURTESY THA INFORMATION DEPARTMENT
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