James M. Cervino
cnidaria at pop.earthlink.net
Sat Mar 9 10:09:10 EST 2002
Hi Ruby, I will answer under your comments below.
RUBY: Something strange happened to one of our study sites recently on the
eastern coast of the island. In fact we noticed at one of our shallowest
monitoring station (approx.1metre) that most of the tabular corals had
bleached completely and died and also most adult eels,holothurians,
octopus, juvenile fish and crustaceans and so on had died and were either
floating to the surface or lying on the sea bed.
JAMES: What were the temperatures? I have exposed corals (Gonipora,
Euphyllia spp. and Acroporids) in the same tank to sub-lethal temperatures
(starting at 28 increasing to 32-33C) which resulted in death to the
Acroporid first via mass expulsion of the symbiotic alga, later the softer
thicker tissue species followed (1 week longer). I became interested and
immediately set up tanks to expose the Acroporid (alone without other
species)to these temperatures. They did expel their algae eventually
leading to bleaching then death. However, this took a few days longer. I
understand these were closed systems which are completely different from
open natural marine aquatic systems. The surface of my tanks and skimmer
were filled with phenols and other chemical compounds (secondary
metabolites?) that might be highly toxic to a neighboring coral or fish.
There is a paper titled chemical defenses mechanisms in corals (sort of
chemical warfare of corals in close proximity) published in the last coral
reef symposium?? (Eric Bornman have you seen this in aquaria? ) Also, the
potential for micro-organisms to switch to pathogenic forms in stressed
hosts has been discussed (Landsberg 1995. Marine Ecology Prog. Series Vol
Were there sponges next to the colonies? Also, sponges when stressed,
produce powerful toxins as a possible defense mechanism. The production of
noxious & odorous substances by sponges has been known in addition to the
ability of some sponge organisms to cause a severe contact dermatitis
(Yaffee & Stargardter, 1963). Toxic and antibiotic compounds from sponges
have been identified (Jakowskaet al 1960; halstead 1965; Nigrelli et al 1967
and Russel 1967). A crude toxic aqueous extract isolated from H. viridis has
been named "Halitoxin" (Baslow et al. 1969). Aqueous extracts of the sponge
Toxa-docia violacea from Hawaiian waters contained hypotensive and paralytic
agents as well (Baslow et al. 1967). If interested e- mail me for a
complete reference list.
This may be one of the many possible explanations why the fish are dying in
the area of dying corals and sponges after thermal stress. These animals
might have been hiding in the crevices of the Acroporids and other corals
exposing them to harmful compounds? The corals are dying due to temperature
increase (considering the temperatures are above the norm during the warmest
month for an extended period (Goreau & Hayes 1994). Stegastes spp. has been
known to be more heat tolerant that some of the Acroporid table-tops
(personal observation). Acroporids seem to be the most sensitive to
temperature stress and chemical exposure (NaCN, copper, gasoline etc.) ,
these species are a good indicator of environmental stress.
To come to such conclusions as to why the fish died, there will be a need to
conduct several tests for the characterization of secondary metabolites.
The selection of novel producing organism's one must use a specific media,
controlled conditions and biochemical manipulations which are all techniques
that enhance the probability of generating novel secondary metabolites.
Isolation, liquid-solid Chromatography is a good way to start. Thanks for
posting this observation !
James M. Cervino
Marine Science Program
University of South Carolina
e-mail:cnidaria at earthlink.net
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