[Coral-List] causes of Acropora loss
Diego Luis Gil
diego.gil at invemar.org.co
Wed Oct 3 16:30:15 EDT 2007
I saw several interesting points on the discussion on Acropora loss. As
some of you know, I conducted some studies on White Band Disease with Dr.
Garriet Smith and Dr. Ernesto Weil couple years ago, although part of it was
published only last year.
I agree with Dr. Bruno, when he said that literature suggests White Band
Disease as probable responsible of Acropora die offs during the 1980´s.
But, I´m not completely sure of this. Please, correct me if I´m wrong, but
diseases hardly affect 100% of the individuals of any population, as
supposedly happened with Acroporas in the 80´s (sorry, I was in high
school). Besides, it is not good for pathogens to do so (who will they
infect next?). If our data is right (and I´m sure it is), the WBD pathogen
is a relatively common Vibrio species (most likely V. carchariae = V.
harveyi), at least for A. cervicornis. We found differences (resistance?)
among organisms, being some of them affected and dying much faster than
others, in the presence of the same pathogen; moreover, disease stopped
after couple days.
Now, in July 2005 during a visit to Rosario Islands (Colombian Caribbean) we
registered a bleaching event, probably the strongest event in the area we
are aware of. During our surveys we visited more than 20 sites and we found
all different coral species bleached up to 10m depth. Nonetheless,
mortality was relatively low (probably no more than 3 or 4%). But,
something came to our attention when we were finishing one of our dives. We
run into an A. cervicornis patch of about 50 m2 and at 3 or 4 m depth, and
we were surprised to find 100% of these corals death, with signs that it was
a recent event (probably no more than couple weeks) and that it affected the
whole area at the same time. Coral branches were all in upright position,
calices were intact, and small algae and cyanobacteria were growing on top
of the bare skeleton. The next day, we decided to go to another patch, this
time A. palmata. Similarly, we found 100% mortality in this site, with
similar conditions to the one described above. There was a difference
though, I visited this last patch 3 months before (April, 2005) and all
corals were alive.
This lead me to think that probably the Acropora loss experimented during
the 1980´s was the product of bleaching due to thermal events. I know this
decade experienced strong Niño events, although I´m not aware of analysis
showing the coincidence or not of these thermal events with reports on
Acropora die offs. To my mind, this is the only kind of event we know that
can produce such massive deaths of these corals in such an ample manner, in
a large geographic scale and in a short period of time.
Diego L. Gil-Agudelo, Ph.D.
Coordinador Biología y Estrategias de Conservación
Instituto de Investigaciones Marinas y Costeras
Cerro Punta de Betín, Zona Portuaria
Santa Marta, Magdalena
Colombia, Sur América
Tel: +57 (5) 421 1380 x 141
Fax: +57 (5) 431 2986
e-mail: diego.gil at invemar.org.co
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