Coral bleaching and flow

[Rob van Woesik]

Dear all,

indeed, water-flow rates influence the extent of coral bleaching.
Increases in water-flow speed enhances the shear stress on a benthic
organism by its square. Shear stress in turn allows the passive
diffusion (i.e., not involving energy) of metabolites (i.e., mass
transfer) or heat across the boundary between the organism and the
ambient environment. As the shear stress increases, resistance to
passive diffusion progressively decreases; thus forced convection
enhances mass transfer. Below, gives reference to a recent paper where
we outline this theory and test whether coral colonies growing in
high-flow habitats are more resistant to high SSTs than colonies in
low-flow habitats. Field evidence, as many of you have also found, shows
higher survival on reefs, or in habitats, with strong currents. We argue
that this is because flow rate will determine the rate of removal of
photosynethic byproducts, or heat, that accumulate under stress (i.e.,
during high SSTs). Obviously, these ideas need further experiments, but
the biophysics and what saw happen on the reefs in 1998 agree.

See Marine Ecology Progress Series 212: 301-304
Nakamura T and Van Woesik R (2001) Water-flow rates and passive
diffusion partially explain differential survival of corals during the
1998 bleaching event.

To download a PDF version see:
http://www.int-res.com/abstracts/meps/v212/index.html

Best Regards

Rob van Woesik

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Dr. Robert van Woesik
Associate Professor
Department of Marine Sciences
University of the Ryukyus
Nishihara, Okinawa 903-0123
JAPAN

E-mail: b984138 at sci.u-ryukyu.ac.jp
Website: http://www.cc.u-ryukyu.ac.jp/~b984138/

Ph: (81) 098 895 8564
Fax: (81) 098 895 8552

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