[Coral-List] coral bleaching: response to Goreau
Andréa Grottoli
grottoli.1 at osu.edu
Tue May 30 15:37:10 EDT 2006
Dear Tom,
I read your contribution on the coral list about
coral bleaching with interest. As the lead
author of the recent Nature paper on
heterotrophic plasticity in bleached corals, I
would like to comment. You stated:
"The recent paper that claims to have discovered "for the first time"
that corals eat zooplankton and can survive bleaching better if fed is
not new either. The fact that corals don't get their carbon from
zooxanthellae is also very old knowledge, but for decades people have
ignored the old literature and have mistaken the net oxygen balance to
assume that corals are also autotrophic in carbon. This recent error has
become dogma, despite being wrong, because nowadays people don't read
the literature or ask those who know it. The first radiocarbon tracer
experiments, done by Thomas F. Goreau and Nora I. Goreau more than 50
years ago showed that very little zooxanthella carbon translocation
contributed to coral carbon, and that corals relied on zooplankton for
the vast bulk of their carbon needs. They kept corals completely
bleached in the dark for years, feeding them on zooplankton. So survival
of bleached fed corals has been known for over half a century and is not
a "new discovery" at all. Like so much else in the current literature."
I would like to point out that our paper showed
that only one species, Montipora capitata,
consumed enough zooplankton to meet all of its
metabolic demand heterotrophically when
bleached. When healthy, M. capitata met less
than 15% of its metabolic demand
heterotrophically. The other two species we
studied, Porites compressa and Porites lobata,
only met 21-35% of their daily metabolic demand
heterotrophically when they were either healthy
or bleached. In all cases, our corals were
exposed to naturally occurring zooplankton on the
reef. Thus under natural reef conditions, not
all bleached corals can meet all of their
metabolic needs heterotrophically. Under
artificially fed conditions (i.e., coral exposed
to higher than ambient concentrations of
zooplankton or brine shrimp in tanks), things can
be quite different. As you pointed out, the
fact that corals do get some fixed carbon from
zooplankton has been know for a very long
time. However, the fact that when bleached at
least one species can increase heterotrophic
feeding to meet all of its metabolic needs while
two others could not, is novel. Our results
suggest that not all species of corals would be
able to meet their metabolic demand when
maintained in the dark under natural
concentrations and abundance of zooplankton (i.e,
P compress and P lobata probably could not get
all of their energy needs met heterotrophically
when bleached under darkness... but this would
need to be specifically tested). In addition,
bleaching induced by keeping corals in the dark
is not necessarily the same as
temperature-induced bleaching. The chain of
physiological stress responses that occur under
high temperature include free radical and stress
protein production, making any heterotrophic
responses under tempreature-induced bleaching
possibly quite different than hetertrophic
responses under sustained darkness.
Sincerely,
Andrea Grottoli
*******************************************************
Andréa G. Grottoli, Assistant Professor
Ohio State University
Department of Geological Sciences
125 South Oval Mall
Columbus, OH 43210-1398
office: 614-292-5782
lab: 614-292-7415
fax: 614-292-7688
email: grottoli.1 at osu.edu
web: www.geology.ohio-state.edu/~grottoli
Office location: 329 Mendenhall Labs
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