[Coral-List] Excess algal symbionts increase coral susceptibility to bleaching

Andrew Baker abaker at rsmas.miami.edu
Wed Nov 21 09:06:53 EST 2012

Dear Gene

After reading Roff & Mumby (2012) I began to wonder the same thing.
Ferrier-Pages et al. (2001) showed that corals exposed to elevated Fe
increased their symbiont densities by about a third, and it's possible this
could affect their thermotolerance. Right now we are running a pilot
experiment where we dosed several coral species with high Fe and we are now
challenging them with thermal stress. It would be interesting indeed if this
does (a) increase symbiont densities, and (b) increase susceptibility to
bleaching, compared to controls. If the effect is detectable at the kinds of
increases in (biologically available) Fe potentially entering from dust,
perhaps it could be a contributing factor in the lower resilience of
Caribbean reefs, as Roff & Mumby suggested. 

A group of us (including Pete Mumby) submitted a proposal to NSF recently,
so hopefully there will be an opportunity to pursue these (and other) ideas
in more detail soon...



Roff G, Mumby PJ (2012) Global disparity in the resilience of coral reefs.
Trends in Ecology and Evolution 27(7): 404-413
Ferrier-Pages C, Schoelzke V, Jaubert J, Muscatine L, Hoegh-Guldberg O
(2001) Response of a scleractinian coral, Stylophora pistillata, to iron and
nitrate enrichment. Journal of Experimental Marine Biology and Ecology 259:

Andrew C. Baker, Ph.D.
Associate Professor, University of Miami 
Pew Fellow in Marine Conservation

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Division of Marine Biology and Fisheries
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Email: abaker at rsmas.miami.edu
Associate Conservation Scientist
Wildlife Conservation Society

-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov
[mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Eugene Shinn
Sent: Friday, November 16, 2012 5:34 PM
To: coral-list at coral.aoml.noaa.gov
Subject: [Coral-List] Excess algal symbionts increase coral susceptibility
to bleaching

Andrew, This is very interesting information especially because you're
findings relate the combined effects of temperature, oxygen, and nutrients
to bleaching.  We certainly have all three, including anthropogenic nutrient
sources, in Florida but I keep remembering the sudden die-off of Acroporids
at San Salvador in 1983. That was a time when there were few anthropogenic
sources on that sparsely populated island surrounded by deep oceanic water.
John Martins original discovery that iron was necessary for algal growth has
been re confirmed by many experiments since then. Because 1983 and 1984 were
peak years for African dust flux to the Caribbean I continue to wonder if it
contained sufficient iron (also phosphate) to provide this necessary micro
nutrient? It is certainly the source of the red soil on that otherwise
limestone island. Could the 5-6 percent iron contained in African dust be
sufficient to cause overstimulation of both cyanobacteria and dynoflagelate
zooxanthellae and thus cause their expulsion i.e. bleaching?
       Considering the co incidence of bleaching events with years of
increased dust flux and warm quiescent summers makes one wonder. The year
1998 was especially warm and dust flux as measured at Barbados by Joe
Prospero was almost as high as it was in 1983 and 1984. With such obvious
correlations one would think that some curious coral biologist would have
performed dosing experiments to validate or discard the dust hypothesis.
Gene  PS: here is a great image of the dust belt provided by Douglas Fenner.



No Rocks, No Water, No Ecosystem (EAS)
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E. A. Shinn, Courtesy Professor
University of South Florida
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<eshinn at marine.usf.edu>
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