[Coral-List] starvation?

[Julian Sprung]

As a follow up to the post I just sent, I have not yet seen this recent paper in Nature and look forward to reading it- My comments about starvation are not in any way intended to dismiss the conclusions of the paper.

I am only commenting on what I believe to be true with regard to temperature induced bleaching and mass die off of corals-- that the majority of the die off usually occurs in a matter of days, far too quickly to be caused by starvation.

It is an interesting point to compare what can be achieved in an aquarium with respect to food inputs as opposed to food supply on reefs. In general the live and particulate food supply on reefs is greater than what is the norm for most aquariums, but I agree aquariums could achieve higher inputs to meet the demands of a particular coral, given the effort of an aquarist to make it happen. The idea that some corals might not be able to get enough food in the wild if they lack zooxanthellae is new to me- if true, it would mean I have to revise my opinion about starvation as being too broad!

Julian



> ----------
> From: 	coral-list-bounces at coral.aoml.noaa.gov on behalf of Andréa Grottoli
> Sent: 	Tuesday, May 30, 2006 3:37 PM
> To: 	coral-list at coral.aoml.noaa.gov; goreau at bestweb.net
> Subject: 	[Coral-List] coral bleaching: response to Goreau
> 
> 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
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