Orange Montastrea cavernosa recruits?

[Charles Mazel]

I concur with Mikhail's comments, and would add that there are other arguments against photoprotection as a general role that fall into the categories spatial, spectral, and ecological.

Spatial-

In many cases the host fluorescent pigments are not distributed over the entire coral surface, and are concentrated along features such as skeletal ridges or polyp mouths.  These features are often exactly where zooxanthellae concentration is low, so the fluorescent pigments would not be affording protection to the light-sensitive algae.

Spectral

The excitation spectrum for the fluorescent pigments often exhibits a minor ultraviolet peak, but the main absorption peak us usually in the visible (ref. Mazel,  1997. Coral fluorescence characteristics: excitation - emission spectra, fluorescence efficiencies, and contribution to apparent reflectance,  Proc. Ocean Optics XIII, SPIE Vol. 2963: pp. 240-245.)  When there is a uv excitation peak it falls in the mid-to-long portion of the UV, above 350 nm.  In contrast, the known uv-protective MAA's referred to in Mikhail's message are more generally distributed and have a clear, strong absorption peak at shorter uv wavelengths that are known to have damaging biological effects.  The MAA's are not fluorescent.

Ecological

The MAA's tend to decrease with depth, as would be expected for a pigment with a photoprotective role.  No corresponding correlation of coral host-fluorescent pigments with depth has yet been found.  It is quite common to find strongly fluorescent corals at relatively deep depths, and non-fluorescent specimens of the same species exposed in shallow water..  The occurrence of the fluorescence is also patchy at any given depth, in the sense that one often finds seemingly quite healthy fluorescent and non-fluorescent specimens of a given species in close proximity.

As a side note, I know that coarl list messages are saved in an archive at the CHAMP web site, but for convenience I have also preserved all of the messages exchanged on the coral fluorescence topic at http://www.nightsea.com/discussion/ under the topic 'Coral-List coral fluorescence discussion'.

Regards,

Charlie Mazel


----------------------------------------------
Charles Mazel
Principal Research Scientist
Physical Sciences Inc.
20 New England Business Center
Andover, MA 01810
(978) 689-0003
(978) 689-3232 (fax)


>>> Mikhail Matz <matz at ibch.ibch.ru> 08/04/00 03:31AM >>>
*** Dear Dr. Murray,
*** thank you very much for your posting. So, here comes the reasoning
against photoprotection function of fluorescent pigments from corals.
These pigments are (in the majority of cases) proteins homologous to
green fluorescent protein (GFP) from Aequorea victoria, as we recently
found out* (Matz et al, Nat.Biotechnol. 17: 969-973, 1999).
*** We already had a bit of this discussion with prof. Ove
Hoegh-Guldberg of the University of Queensland (oveh at uq.edu.au), who was
also suggesting photoprotection as the major role of fluorescent
proteins. Here is a part of what I wrote to him directly in responce:

Concerning photoprotection I would rather disagree with you. First of
all, corals possess a multitude of low-molecular sunscreen
compounds for this purpose (see, for example, Dunlap, W.C. et al.
Nature's sunscreen from the Great Barrier Reef, Australia. International
Journal of Cosmetic Science 20, 41-51 (1998)), so additional recruitment
of specialized proteins
for the same purpose seems rather tedious. Still, if it still was
protection from UV, there is no difference which
fluorescent color to use - green or red, they are both UV-excitable.
Meanwhile, our most recent data on molecular features of red-emitters
suggest that they are advanced versions of greens, so that a point
mutation would most likely damage
the red protein making it green. Therefore, red color should have some
special role in nature (different from green!)
to be maintained by natural selection, otherwise all the red-emitters
would have long since deteriorated into greens due to mutation pressure.
In addition, red-emitters are heavily suboptimal in comparison to greens
in terms of photoprotection - they all have much lower quantum yields of
fluorescence.

*** So, I think that the coral fluorescence file is still far from being
closed.
*** I would be happy to continue this discussion, especially taking in
account that the question of the fluorescent proteins function in corals
is exactly the subject of my current research.

sincerely yours

Mikhail Matz, Ph.D.
Institute of Bioorganic Chemistry
Miklukho-Maklaya 16/10
117871 Moscow, Russia
*

Robert Murray wrote:

> Hi Iain et al,*Coral photobiology is not my area of study, although I
> did examine the topic some years ago. I believe it is fairly common
> for many corals to exhibit brightly coloured fluorescence pigments
> (especially those in shallowest water conditions where light intensity
> is greatest).*From some of the literature I have read I seem to
> remember a plausible case for these pigments operating as some sort of
> protection against the destructive energy of short (UV) wavelengths,
> by liberating some of this energy as harmless (less energetic) visible
> fluorescence. Perhaps this is one of the discredited theories now. If
> so, I would be interested to hear the evidence against it.*Regards to
> all*Robert Murray.**(What's up Iain?)**=======================
> ROBERT MURRAY* BSc, FGA,
> Discovery Bay Marine Laboratory,
> Discovery Bay, Jamaica, W.I.
>
> Tel. (876) 973 2946
> Fax. (876) 973 3091
> rmurray at infochan.com 
> www.DBML.ORG 
> =======================*
>