Perhaps you need to do a bit more reading ...

EricHugo at EricHugo at
Thu May 10 13:28:10 EDT 2001

Hi Debbie and list:

I read your post, your paper, and Ove's comments.

I must say I question your choice to take on Ove in this, of all, subjects 
;-)  But if I might offer a few comments?  I trust the list members will 
correct me if I am mistaken, as I am not actually pulling the many papers 
from which the following are drawn:

First, the lipid content of coral mesenteries can vary greatly not only 
because of environmental conditions, but also due to species physiology 
(mesentery size, respiration rate, etc.), with some corals able to exist on 
stored lipid content up to 100 days, if I recall correctly.  Second, warming 
water tends to encourage reproduction, and spawnings happen during the warmer 
months...this includes many animals forming the plankton that corals feed 
on...Much, if not most, of the plankton on coral reefs is produced and dwells 
in, and migrates upward nightly on the reef, and is not pelagic.  The pelagic 
plankton is a component, but probably is significantly lost by fish grazing 
on the fore-reef slope.  Other planktonic inputs come from nearshore areas 
being flushed outward by tidal changes.

Corals are also mixotrophic (polytrophic) and do not depend on single 
heterotrophic sources.  They can absorb significant amounts of DOM ("liquid 
nutrients" as you put it).  Further, many feed on detritus (coral mucus, 
algal debris, bacteria, agglomerations of other microorganism, etc.)  This is 
a rich food source well documented in the literature. Some corals may even 
obtain their largest percentage of energy obtained by feeding from this 
source, including the soft corals that also bleach.  In the absence of one 
food source, they can shift to obtaining required energy from other food 
sources.  Detritus, being formed of such material, especially N-rich bacteria 
and coral mucus, would, if anything, increase during warmer months.

Also, the energy obtained by light and zooxanthellae is carbon rich, mostly 
lost as mucus, whereas heterotrophic acquisition tends to be more weighted 
toward N and contributes towards growth and reproduction.  If anything, high 
N would allow more to be excreted or to be present in a non-limiting N 
environment, perhaps even allowing the zooxanthellae to slow their synthesis 
and translocation of glycerol and other photosynthate and using it to produce 
proteins, resulting in unbalanced growth, and perhaps even exacerbating a 
potential bleaching situation by overly high densities within the 

Also, your understanding of the bleaching mechanism, literature on the 
subject, and the results of free oxygen, peroxide, etc. in the bleaching 
response are not shown by your web page.  In terms of growth, warmer temps 
increase calcification up to point, and corals live optimally up to near a 
few degrees of their upper thermal limit,  So reduced growth is not really 
the case.  Also, warming waters are involved in coral spawning and gonad 
maturation, so the comment on decreased reproduction is not quite right 

The patchiness of bleaching was discussed on the list a while back, and 
stagnant areas due to flow dynamics even around a coral  colony can result in 
local conditions that exacerbate bleaching.  

Finally, the web page sort of reads in a sensationalist manner, in my 
opinion, that I don't think adds to its credibility.  

Just my thoughts,

Eric Borneman
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