Coloured Pigments and Coral Bleaching?

[Robert W. Carter]

Rupert,

I have been studying coral pigmentation (fluorescent proteins) for several
years. During this time, I have been able to witness changes in
pigmentation of Caribbean corals due to both natural and laboratory
bleaching. I do not know much about the (apparently) non-fluorescent
pigments found in many Indo-Pacific Acroporid corals (the blues and pinks
you mention), but here are a few things I have learned about the closely
related fluorescent proteins (this will be from a Caribbean perspective):

1. Corals do not necessarily go completely white during bleaching.

I have seen individuals of Montastraea cavernosa displaying a bright
pinkish-red fluorescence after bleaching. Mikhail Matz' recent post said
something similar but for a completely different group. On more than one
occasion and in more then one location, I have seen bleached Montastraea
faveolata colonies with their nearly clear tissues exhibiting a bright
green fluorescence. These colonies survived the bleaching episode.

2. Even if one can not detect fluorescence by eye in daylight, it may still
be possible to see it under the right optical conditions.

"Non-fluorescent" corals are often fluorecent under UV or blue excitation,
especially when viewed under a fluorescence dissecting microscope.
Therefore to say that an animal is "white" may not be accurate, although
there may be obvious changes in color or intensity.

3. Individual corals MAY retain coloration for some time after bleaching.

I have observed laboratory specimens bleach and recover after several weeks
but never completely lose their green color.

To directly address your question:

The zooxanthellae are expelled first. The animal-derived fluorescent
proteins seem to degrade over time. Sometimes quickly, but not always. The
rate of loss may be dependent upon the degree of stress. Is this an
adaptation whereby the coral is adjusting its coloration to enhance what
little photosynthesis it can muster or is it a stress response where the
coral is metabolising a vital store of protein? I don't know but I suspect
the latter.

Rob Carter
University of Miami

At 10:48 AM 5/28/2002 +0100, you wrote:
>Dear Coral Listers
>
>I would be grateful if any of the coral physiologists involved in bleaching
>work could offer any details on a question that's been put to me a couple
>of times.
>
>The colourful pigments (blues, pinks etc.) that are charateristic of many
>shallow water corals (Acropora etc.) are, as I understand it, located in
>the coral tissue itself.  Whereas the pigments present in the zooxanthellae
>are more or less brown in colour.  If coral bleaching (due to elevated
>SSTs) is principally the result of expulsion or loss of zooxanthellae, then
>why do the corals go completely white.  i.e. what happens to the more
>colourful coral pigments? Are they damaged as well but independently by
>temperature induced failure of protective systems?
>
>sincerely,
>
>Rupert Ormond
>
>
>
>
>Dr. Rupert Ormond
>Director,
>University Marine Biological Station Millport,
>Isle of Cumbrae,
>SCOTLAND
>UK  KA28 0EG
>
>email: rupert.ormond at millport.gla.ac.uk
>tel: (44)-01475-530581
>fax: (44)-01475-530601
>web: http://www.gla.ac.uk/Acad/Marine/
>
>
>
>~~~~~~~
>For directions on subscribing and unsubscribing to coral-list or the
>digests, please see http://www.coral.noaa.gov/lists/coral-list.html .
>
>

~~~~~~~
For directions on subscribing and unsubscribing to coral-list or the
digests, please see http://www.coral.noaa.gov/lists/coral-list.html .