Ove Hoegh-Guldberg oveh at
Sun Dec 6 19:18:38 EST 1998

Dear Martin,

I would recommend you read a paper that we have in the journal Plant, cell
and Environment.  It should be out (or will be soon - I can fax you a copy).
The basic finding is that slight increases in temperature cause a stalling
of the dark reactions of photosynthesis - that is, bleaching is akin to a
lowering of the threshold of symbiotic dinoflagellates for photoinhibition.
Our model currently suggests that temperature causes a failure of electron
flow to the Calvin Cycle and subsequent electron pressure from the light
reactions leads to over-reduction of electron transport components and
(probably) active oxygen production.  This results in damage to the
dinoflagellate symbionts and eventually in coral bleaching.

Jones, R, Hoegh-Guldberg, O, Larkum, AWL and Schreiber, U. (1998)
Temperature induced bleaching of corals begins with impairment of dark
metabolism in zooxanthellae. Plant Cell and Environment.  Abstract below.

We can also simulate the same effect by stalling the flow of carbon dioxide
to the Calvin Cycle using inhibitors of CA, increasing light pressure,
blocking the dark reactions using cyanide and other means.  Your experiments
demonstrate a similar effect - a reduction in the flow of carbon to the
Calvin Cycle and subsequent over-reduction etc.  I would predict that your
effect is light dependent and that the effect is vastly reduced if your
experiments are done in the complete absence of light.

Given the extremely high coincidence between thermal anomalies and coral
bleaching, I would still say that even though you get this effect in the
laboratory, it is still a (perhaps important) secondary factor like light
intensity.  Your message header, then, "BLEACHING IS DUE TO CO2" is

I look forward to hearing from you.




Temperature induced bleaching of corals begins with impairment of dark
metabolism in zooxanthellae (86 characters)

Running title: Temperature induced bleaching of corals (35 characters)

List of authors:

(a) R.J. Jones 1
(b) I.O. Hoegh-Guldberg 1
(c) A.W.D. Larkum 1
(d) U. Schreiber 2

Institutes of origin:

1School of Biological Sciences, The University of Sydney, Sydney NSW 2006,

2 Julius-von-Sachs Institut für Biowissenschaften, Universität Würzburg,
Mittlerer Dallenbergweg 64, D-97082 Würzburg, Germany

Name and address of author to whom correspondence should be addressed:

Dr Ove Hoegh-Guldberg
Building AO8
School of Biological Sciences
University of Sydney
Sydney, NSW 2006
Telephone: (02) 9351-2389
Fax (02) 9351-4119
email: oveh at

The early effects of heat stress on the photosynthesis of zooxanthellae
within the tissues of a reef-building coral were examined using
Pulse-Amplitude-Modulated (PAM) chlorophyll fluorescence and
photo-respirometry. Exposure of Stylophora pistillata to 33 and 34(C for 4 h
resulted in (1) the development of strong non-photochemical quenching (qN)
of the chlorophyll fluorescence signal, (2) marked decreases in
photosynthetic oxygen evolution, and (3) decreases in optimal quantum yield
(Fv/Fm) of photosystem II (PSII). Quantum yield decreased to a greater
extent on the illuminated surfaces of coral branches rather than lower
(shaded) surfaces, and also when high irradiances intensities were combined
with elevated temperature (33(C as opposed to 28(C). qN collapsed in
heat-stressed samples when quenching analysis was conducted in the absence
of oxygen. Collectively, these observations are interpreted as the
initiation of photoprotective dissipation of excess absorbed energy as heat
(qN) and O2-dependent electron flow through the Mehler-Ascorbate-Peroxidase
cycle (MAP-cycle) following the point at which the rate of light-driven
electron transport exceeds the capacity of the Calvin cycle. A model for
coral bleaching is proposed whereby the primary site of heat damage in the S
pistillata is carboxylation within the Calvin cycle, as has been observed in
the higher plants. Damage to PSII and a reduction in Fv/Fm (cf
photoinhibition) is a secondary effect following the overwhelming of
photo-protective mechanisms by light, a secondary factor that aggravates the
effect of the primary variable temperature. Potential restrictions of
electron flow in heat-stressed zooxanthellae are discussed with respect to
Calvin cycle enzymes and the unusual status of the zooxanthellar Rubisco.
Significant features of the model are that (1) damage to PSII is not the
initial step in the sequence of heat stress in zooxanthellae, and (2) light
plays a key secondary influence.
(words 293)

-----Original Message-----
From:	owner-coral-list at
[mailto:owner-coral-list at] On Behalf Of MARTIN PECHEUX
Sent:	Monday, 7 December 1998 1:55
To:	coral-list at

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.

Otherwise, if you have proposition
for a job, thanks.

Martin Pêcheux
IUFM Sciences Vies et Terre,
University of Nice
15 bis, rue des Roses, 06100 Nice -
Tel +33 492 071 079

More information about the Coral-list-old mailing list