[Coral-List] when do we decide a coral is bleaching ?

[Mathieu POULICEK]

Bonjour à tous,

I was asking myself if anybody already put a 
limit to what we call "bleaching" ?
Coral regularly expell zooxanthellae that are 
found in the mucus sheets close to the "feet" of 
the colonies. This probably constitutes a 
regulation behaviour correlated to the algae 
division rates in order to keep a stable 
symbiotic population. From an experimental point 
of view, we can measure that the expelling rate 
varies according to different not well understood factors (to my knowledge).
When does this behaviour begin to be pathologic ? 
The zooxanthellae content of a given colony can 
fluctuate in "normal" conditions.
Some situations are obvious, when the coral loose 
a great part of its algae content and "bleach 
clearly" but some other are much less clear.
Is there a formal "definition", some limits clearly defined ?
What do YOU think about that limit ?
I am waiting your returns.

Have a nice day,
Bonne journée à tous,

Mathieu Poulicek
PS If there is interest I can put a digest of answer on the list later.

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Dr  Mathieu POULICEK, Chargé de cours adjoint
Coordinateur départemental ERASMUS Biologie
Tel lab : 32- (0)4 -366.50.67    Tel. prive : 32- (0)4 -355.06.74
Fax : 32- (0)4 -366.51.47
e-mail: mpoulicek at ulg.ac.be

     Unite d'Ecologie Marine, Laboratoire 
d'Ecologie animale et d'Ecotoxicologie,
     Département des Sciences et Gestion de l'Environnement,
     Institut de Chimie B6C, Universite de Liege
     Allée du 6 août, 15
     Sart Tilman, B-4000 Liège (Belgique)
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