[Coral-List] Does enhanced water movement increase or decrease bleaching sensitivity?

Scott Wooldridge swooldri23 at gmail.com
Tue Aug 22 19:18:06 EDT 2017

Hi Tim Wijgerde, and fellow coral reef researchers;

Congratulations on the new manuscript


Indeed, i believe that targeted experimentation on water flow impacts on
coral bleaching sensitivity is an excellent place to make inference about
the importance of CO2-limitation on coral physiology.

Strangely enough, the theory would suggest that bleaching sensitivity
increases at very low flows (<10 cm/s i.e. mass transfer limitation). But
that continuous high flows can be equally detrimental - but only in areas
where symbiont dynamics are not constrained by nutrient limitation (i.e.
nutrient replete areas - typically inshore or offshore upwelling areas).
That is, the high mass transfer rate caused by high water flow can increase
supply of CO2 and inorganic nutrients - thus raising ambient zooxanthellae
densities, and bleaching sensitivity under stress.

McClanahan et al. showed good field evidence of this dynamic in Mauritius.


In 2011 I submitted a manuscript entitled, 'Does enhanced water flow
increase or decrease the risk of coral bleaching? A review and new working
hypothesis". The manuscript was rejected by all x3 reviewers and was very
harshly criticised. New research findings in this area since then only make
me more convinced that it is correct. And given time, i hope to rework and
resubmit with the new evidence.

I have attached that submitted manuscript attached within:


At the time, the reviewers were particularly scathing of my my inference
that this dynamic implies that current day seawater pCo2 ~400ppmv is
already beyond the optimal limits for the coral-algae symbiosis.

But i have since used other lines of evidence to support the claim that the
coral-algae symbiosis is most optimal when pCO2 <260-280 ppm. And hence,
why water flow impacts on coral bleaching is multifaceted in the present


I am more than happy to expose myself to the risk of ridicule by putting
the challenge out to all  experimental scientists is to test these
"theoretical predictions" in the lab - aim to prove it wrong. Even if it is
wrong we will learn something new - this is good science practice. science
without politics. Just ensure that irradiance levels under bleaching stress
testing are high enough to induce CO2-limitation (i.e. >500 umol/m2/s)



cited literature:

McClanahan TR, Maina J, Moothien-Pillay R, Baker AC (2005) Effects of
geography, taxa, water flow, and temperature variation on coral bleaching
intensity in Mauritius. Mar Ecol Prog Ser 298:131-142

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