[Coral-List] Excess algal symbionts increase coral susceptibility to bleaching
abaker at rsmas.miami.edu
Fri Nov 16 11:15:43 EST 2012
Very interesting idea about O2 demand -- Ross and I hadn't thought of it
that way before, but it fits with the idea that corals have to balance the
costs and benefits of symbiosis, and that these costs and benefits are
highly density-dependent (i.e., affected by the number of symbionts a coral
has). Increased O2 demand at night could be another significant cost of
hosting high symbiont densities (perhaps exacerbated by doldrum conditions),
and the coral would thus be competing with its own symbionts for oxygen.
Maybe this would be an interesting idea to test using microelectrodes within
the coral tissues...? Do corals with more symbionts become more hypoxic at
night compared to corals with less symbionts? Can prolonged hypoxia in coral
tissues trigger coral bleaching? Or might the coral regulate its symbiont
density to compensate...? (sort of a form of coral bleaching in itself).
Either way, it's another example of potential tradeoff between having enough
symbionts to make a living from autotrophy, while not having so many that
they present other challenges. There is a very thought provoking paper by
Scott Wooldridge on these kinds of themes as well (reference below).
Thanks for bringing it up!
Andrew & Ross
Cunning R, Baker AC (2012) Excess symbionts increase the susceptibility of
reef corals to bleaching. Nature Climate Change. doi:10.1038/nclimate1711
Wooldridge SA (2012) Breakdown of the coral-algae symbiosis: towards
formalising a linkage between warm-water bleaching thresholds and the growth
rate of the intracellular zooxanthellae. Biogeosciences Discuss., 9,
Andrew C. Baker, Ph.D.
Associate Professor, University of Miami
Pew Fellow in Marine Conservation
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Email: abaker at rsmas.miami.edu
Associate Conservation Scientist
Wildlife Conservation Society
From: Billy Causey [mailto:billy.causey at noaa.gov]
Sent: Thursday, November 15, 2012 2:35 PM
To: abaker at rsmas.miami.edu
Cc: coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Excess algal symbionts increase coral
susceptibility to bleaching
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
305 809 4670 office
305 395 0150 mobile
305 293 5011 fax
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:
> Press release:
> Reference: Cunning R, Baker AC (2012) Excess symbionts increase the
> susceptibility of reef corals to bleaching. Nature Climate Change.
> Pdf available on request from lead author Ross Cunning
> (rcunning at rsmas.miami.edu)
> Andrew Baker
> Andrew C. Baker, Ph.D.
> Associate Professor, University of Miami
> Pew Fellow in Marine Conservation
> Lab webpage link here
> Google Scholar profile link here
> Visit the lab on Facebook by clicking
> esearch-Lab-CR2/149751198419595> here
> Division of Marine Biology and Fisheries
> Rosenstiel School of Marine and Atmospheric Science
> University of Miami
> 4600 Rickenbacker Cswy.
> Miami, FL 33149, USA
> Office: +1 (305) 421-4642
> Lab: +1 (305) 421-4226
> Fax: +1 (305) 421-4600
> Email: <mailto:abaker at rsmas.miami.edu> abaker at rsmas.miami.edu
> Associate Conservation Scientist
> Wildlife Conservation Society
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