[Coral-List] Water temperatures and organism responses
esther.peters at verizon.net
Wed Jun 18 19:50:35 EDT 2008
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
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