[Coral-List] Water temperatures and organism responses

[Esther Peters]

All,

I want to call your attention to a paper (PowerPoint presentation and 
notes presented earlier this year at the Florida Academy of Sciences) in 
which temperature logger data collected from benthic stations off St. 
Petersburg and the Florida Keys are compared with SST records.  Go to 
http://delta-seven.com/publications.html to download these files.

This look at "what the organism sees" makes me think the coral bleaching 
story is much more complex, not only from a habitat perspective, but 
from an individual colony perspective.  The often daily fluctuating 
pattern of temperatures to which benthic organisms are adapted suggest  
that homeostatic mechanisms operate to keep coral/zooxanthellae 
metabolic cycling pathways capable of recovering from short (hours) 
pulses of warmer water exposure.  Laboratory experiments to examine heat 
stress have not (to my knowledge) looked at these finer scale 
fluctuating temperature adaptations, which might be due to changes in 
insolation, tides, rainfall, or other factors.  And in situ temperatures 
can be different from the SST readings, even higher, or much lower.

Because I have seen histologically that "bleaching" can be associated 
with exocytosis of zooxanthellae, death of the symbiotic algae within 
the gastrodermal cell (bacterial toxin-mediated or other factor?), 
replacement of zooxanthellae by intracellular parasites (perhaps by 
competition for nutrients or toxin secretion, still unknown), and 
sloughing of the gastrodermis,  and associated with increased or 
decreased temperatures or not, salinity changes, shading, sedimentation, 
etc., we should be more inquisitive about how this condition develops 
and what these temperature data mean for habit and other organisms, too.

Esther Peters, Ph.D.
George Mason University
epeters2 at gmu.edu