delbeek at waquarium.org
christine.schoenberg at mail.uni-oldenburg.de
Thu Oct 4 06:59:32 EDT 2001
Charles Delbeek wrote:
At 01:45 PM 10/1/2001 +0200, you wrote:
> >they have all come up with the same answer: on "normal" reefs,
> >bioerosion and calcification are in approximate balance. On most fringing
> >reefs, subject to increasing terrestrial nutrient input, therefore, the
> >balance has already been shifted towards destructive processes.
>This matches my own experiences when working on the Central Great Barrier
>Reef, where the balance may still be better than most other places. We
>still need to keep an eye on it though.
>The common sponge Cliona orientalis reacts to elevated nutrient conditions.
>_Extreme_ situations may have negative effects, however, so that the
>sponge's growth is slowed. Bioerosion of this sponge appears to be enhanced
>by a higher concentration of nutrients. This is a sponge, which is just
>everywhere on Australian (and other Pacific) inshore reefs, which grows
>over large surfaces, several m in diameter and which is able to invade live
It seems the word "nutrient" is a bit of a catch-all phrase when it comes
to describing decline of reef organisms. Has some demarcation been
demonstrated as to which "nutrients" have what negative effects i.e.
organic vs. inorganic? nitrogen vs. phosphorous? increases of elements
normally considered minor or trace?
J. Charles Delbeek
2777 Kalakaua Ave.
Honolulu, HI, USA 96815
even though sometimes a quick comment can be sufficient you are right to
ask. I will elaborate for better understanding:
I conducted one experiment at the Townsville Aquarium, being allowed to set
up my sponge grafts in the two big exhibit tanks. The Aquarium provided me
with data about water conditions in those tanks. Whereas the average
nutrient level in the reef tank was 0.3 microMol NO2/3, the concentration
was 600 microMol NO2/3 in the shark tank. I did not receive information
about P-levels. Flow strength was between 13 and 31 cm/sec, depending on
the site. My results indicated that higher flow rates were overall positive
for the sponge, whereas the very extreme nutrient condition in the shark
tank generally affected the sponge negatively (lower growth rate), but it
increased the bioerosion rate. Not all results were significant, however.
Overall it can be said that the sponge survived and functioned in the shark
tank, despite the extreme conditions. The grafts grew onto and into the
limestone blocks I attached them to. The experiment ran for about 7 months.
There was another experiment where I investigated particle load (POM,
measured by photometry and nutrient analysis of different components) as
influence the sponge's functions. This experiment didn't work out the way I
wanted it, because the sponge grafts gradually died off in the tanks.
However, they survived best in the tanks with filtered seawater and in the
tanks, which contained particle-enriched seawater. This is a somewhat
puzzling result, but there may be a trade-off between benefits from the
symbiotic zooxanthellae and the filter feeding. Anyway, I didn't evaluate
this experiment in detail, because of the poor results.
I am presently busy preparing similar studies on bioeroding sponges and
will keep people informed.
Dr. Christine Schönberg, PhD
Dept. of Zoosystematics & Morphology
Fachbereich 7 - Biology, Geo- & Environmental Sciences
Carl von Ossietzky University Oldenburg
email christine.schoenberg at mail.uni-oldenburg.de
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