[Coral-List] Excess algal symbionts increase coral susceptibility to bleaching

[Billy Causey]

Andrew,
Once again, you and your students are doing some cutting edge
research.  Congratulations to you and Ross!

At great risk of generating a debate of some sort, I wanted to share
some thoughts pertaining to your findings in this current paper.

Just prior to and during the massive bleaching in the Florida Keys
(1983, 87, 90, and 97-98) we had slick-calm, doldrum weather for weeks
at a time.  Prior to the onset of bleaching, the reef fish would
appear stressed (pumping opercula), as if there was low O2 in the
water.  The seas were slick, the water was hot, day and night .... and
everything was demanding O2 at night. Even the symbionts living in the
coral tissue.  Now, you have discovered that corals with more
symbionts are more susceptible to bleaching.  To me, that translates
to possibly meaning there are more symbionts demanding or using O2 at
night in the coral tissue.  I have always felt that the role of
dissolved O2, especially at night, was another factor that contributes
to triggering coral bleaching.

Imagine, you are the tissue of a coral, stuffed with symbionts, and
the water is hot, DO is low, even during the day, nightfall comes,
photosynthesis stops at night, everything is demanding O in the coral
tissue, even the crowed symbionts.  This cycle goes on day and night
for the extent of the doldrum weather.  The coral tissue and symbionts
compete for O2, especially at night .... and soon something has to
give.  The symbionts are either expelled or consumed .... and
bleaching occurs.

I realize this is rather simplistic, but it is something that I have
thought about for years.

Your's and Ross' research triggered my thinking again about the role
of symbionts and levels of DO in the reef community.

Again, congratulations for a great paper!   Billy

Billy D. Causey, Ph.D.
Southeast Regional Director
NOAA's Office of National Marine Sanctuaries

33 East Quay Road
Key West, Florida 33040

Phone:
305 809 4670 office
305 395 0150 mobile
305 293 5011 fax

Email:
billy.causey at noaa.gov


On Nov 12, 2012, at 8:55 PM, Andrew Baker <abaker at rsmas.miami.edu> wrote:

> Dear all
>
>
>
> A paper published recently in Nature Climate Change might be of interest to
> list subscribers. It shows that corals with too many algal symbionts are
> more susceptible to bleaching, contrary to conventional wisdom that corals
> with more symbionts are protected from bleaching because they have "more
> symbionts to lose". It suggests that corals have to balance maximizing the
> photosynthetic benefits provided by their algal symbionts against the risk
> of having too many symbionts if exposed to high temperatures.
>
>
>
> This has some real world implications, providing a mechanistic explanation
> for why corals exposed to nutrient pollution are more sensitive to bleaching
> (see also Wiedenmann et al. 2012 for another, not necessarily mutually
> exclusive, mechanism). It may also influence the bleaching susceptibility of
> corals exposed to increasing pCO2.
>
>
>
> Link to paper:
> http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1711.html
>
> Press release:
> http://www.rsmas.miami.edu/news-events/press-releases/2012/too-much-of-a-goo
> d-thing-can-be-bad-for-corals/
>
> Reference: Cunning R, Baker AC (2012) Excess symbionts increase the
> susceptibility of reef corals to bleaching. Nature Climate Change.
> doi:10.1038/nclimate1711
>
>
>
> Pdf available on request from lead author Ross Cunning
> (rcunning at rsmas.miami.edu)
>
>
>
> Sincerely
>
> Andrew Baker
>
> ___________________
>
> Andrew C. Baker, Ph.D.
>
> Associate Professor, University of Miami
>
> Pew Fellow in Marine Conservation
>
>
>
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