RWD vs Sparisoma

[Jaime Garzon]

Dear colleagues:

Regarding RAPID WASTING DISEASE (RWD) vs PARROTFISH GRAZING discussion, I
would like to share my observations and tell you that I think both Goreau et
al. and Bruckners are rigth about the existence of these two agents of coral
mortality.

Since early 1980's I have studied coral reef organisms in the Colombian
Caribbean, and from that time I observed intense coral predation by
Sparisoma viride, especially on large Colpophyllia natans coral heads. I saw
many times big specimens of this parrotfish removing large portions of the
soft upper layer (2-3 cm deep) of living tissue + skeleton of C. natans, as
described by the Bruckners ("... in a band, moving methodically across the
coral"). The recently exposed large skeleton areas were clean white, and
large heads of this coral were totally denuded and superficially eroded
within a couple of weeks.

On the other hand, while evaluating coral reef health of several Colombian
Western Caribbean atolls, we observed RWD since 1994, but it was initially
confused with bleaching. On May-June 1995, I realized that "White Patches"
(as we named it by then) was a different condition. So we obtained separated
data on the incidence and distribution of this new disease only from
Roncador atoll, where it was present only at the lagoonal reefs on about 24%
of Montastraea annularis (sensu stricto) colonies. This coral is probably
the most abundant at this environment there, so the incidence of RWD was
considerable. As has been described by Dr. Goreau and colleagues, RWD is
characterized by leaving white irregular patches without tissue in the coral
surfaces, with a very sharp boundary between the colored living areas and
the white dead areas. Nevertheless, I observed these conspicuous "white
patches" principally near the margins of living portions of the colonies,
and good preserved skeletal surfaces in the recently dead areas.

If both RWD and S. viride are causing similar surface erosion of the
skeleton while attacking living coral surfaces, it is something that needs
to be confirmed and studied in detail. Meanwhile, we have to be very
cautious when trying to assign responsability for recently dead eroded areas
of coral surfaces.

Best regards,

Jaime Garzon-Ferreira
INVEMAR, 
Santa Marta, Colombia

Jaime Garzon-Ferreira

Instituto de Investigaciones Marinas y Costeras - INVEMAR
A.A. 1016, Santa Marta, Colombia (S.America)
Tel. (57-54) 214774 or 214775 or 211380 - Fax (57-54) 211377
E-mail: jgarzon at santamarta.cetcol.net.co