[Coral-List] Temporal colour change of coral from green to red

mikhail matz matz at whitney.ufl.edu
Thu Jul 6 11:10:55 EDT 2006

Hi Terry and all,

Very interesting observation!

Not counting the brownish hue provided by zooxanthellae pigments, there 
are four basic colors: fluorescent green, red and cyan (this one is kind 
of bluish, looks gray underwater), plus intense non-fluorescent purple 
that may look dark blue underwater (most common in Portitidae, 
Acroporidae and Pocilloporidae). Oftentimes you would have differently 
colored domains such as oral disk, caenosarc and tentacles (Faviidae), 
or caenosarc, tentacles and the rim of the corallite (Acroporidae). 
Purples tend to be located on colony extremities - branch tips or 
growing edges (this seem to apply to some extent to reds as well). So it 
is quite natural that when the tentacles are colored differently than 
caenosarc the appearance would change when the tentacles are retracted; 
however, I must admit that I never encountered a coral in which the 
effect would be really as pronounced as it seems to be from Terry's 
message (what was that coral, Terry?..).   Changes in the coloration of 
the domains throughout the lifetime of a colony seem to happen extremely 
slowly if happening at all (with the exception of cases when damaged 
zone starts regenerating and expressing reds or purples that were not 
there before; after regeneration the zone settles back to the appearance 
of the surrounding undamaged polyps); but admittedly we need to look 
into that more accurately.



Terry F. F. Ng wrote:
> Have anyone ever observed or recorded corals that can temporally change
> their colour?
> Recently I have been observing a green coral that can temporarily change to
> red within a second. The extended tentacles are originally green in daytime,
> making the colonies green. When the corals were touched, the tentacles
> retracted and revealed the red outer layer, then the whole colonies appears
> to be red. I guess there are some advantages associated with this colour
> change: better protection with red colour when it is stimulated. Also, it
> may be good to be green at daytime when the tentacles are extended, and be
> red (or appeared to be dark) at night when the tentacles are retracted.
> I am very curious whether other people have noticed this kind of coral.
> Anyone might also contact me for further information.
> Terry Ng
> terryfeifan at gmail.com
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> Coral-List mailing list
> Coral-List at coral.aoml.noaa.gov
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Mikhail V. Matz
Whitney Laboratory for Marine Bioscience
University of Florida
9505 Ocean Shore Blvd
St Augustine FL 32080
phone 904-461-4025
fax 509-562-4749
web www.whitney.ufl.edu/research_programs/matz.htm

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