BLEACHING IS DUE TO CO2

[J. Charles Delbeek]

On Sun, 6 Dec 1998, MARTIN PECHEUX wrote:

> Dear Coral-listers This work was presented (and can be quoted as "Link
> between CO2 rise and bleaching proved by fast fluorescence kinetics") at
> the 4th Europ. Meet. Coral Reef, Perpignan, France, 1-4 Sept.1998, p.
> 138.  I have done many bleaching experiments on corals, anemones and
> large foraminifers, short- and long-term, with systematic light,
> temperature and CO2 synergies. They were monitored by fast kinetics of
> chlorophyll fluorescence rise (quantum efficiency of absorbtion,
> trapping, transport, later processes, i.e. photosynthesis stress
> measures). I gathered more than 100 000 data.  As I hypothesized in late
> 1991 (cf.  my Review on Internet), CO2 rise and induced seawater
> acidification (-0.0853 pH, 21percent more H+) is indeed an important
> bleaching factor : a) it is very complex in details with time,
> synergies, taxons, etc ; b) CO2 is as much important as temperature for
> bleaching ; c) SPECTAULARLY it has the same physiological effect than
> temperature ; one pH less is like >>4.1 C.  Thus actual CO2 rise is a
> bleaching stress exactly equivalent to at least 0.4, surely 1.2 degree
> morE, strongly synergical with increasing light and temperature. I now
> consider prooved that CO2 rise is directly a (the) main bleaching
> factor. And I have good indications that the origin of bleaching is
> impairement of electron transport between the quinone A and B of the
> D1-D2 photosystem II site (photoinhibition s.s.).  Future CO2 level with
> a "business as usual scenario" would correspond to 5 degrees more during
> sunny summer : this is an announciated catastroph ("best guest" 90-98
> percent species death ??). A proposito, observed recent shell
> abnormalities of bleaching large forams proves that : a) mass bleaching
> is a new phenomenon ; b)  it can be compared only to the
> Cretaceous-Tertiary boundary : 10 millions years reef disappearence.  An
> article is of course in preparation. Call me if you need sooner more
> informations for your own research, or for vulgarization/political
> reasons. 

Dear Martin,

I am curious to know how rapidly the pH was decreased or was it a gradual
process? In closed systems corals can be induced to bleach by rapid
changes in almost any environmental parameter you wish to name e.g.
temperature, light intensity, alkalinity, UV etc.

However, our closed live coral systems often fluctuate from a low pH of
8.10 in the morning to a high of 8.35 in the late afternoon. We do not see
any bleaching occuring. We also have been culturing corals for over 10
years in systems fed from a saltwater well whose pH is generally 7.5-7.8. 
Water temperatures in our systems range from lows of 75-77 oF in the
winter and highs of 80-84 oF in the summer. Again no bleaching.

How would you explain these observations in light of what you have written
above? As Ove pointed out, CO2 changes may induce bleaching but so do many
other things. To state that CO2 is possibly the cause of coral bleaching
may be a bit presumptuous, but rather, as you stated, its synergistic
relationship with temperature and light levels (and probably UV) adds
another piece to the puzzle.


J. Charles Delbeek 

Aquarium Biologist
Waikiki Aquarium
University of Hawaii