[Coral-List] Filter feeding bivalves for improvements in coastal water quality

David Fisk davefisk at gmail.com
Wed May 28 13:46:16 EDT 2008

I am not sure it is as simple as what you propose in attempting to
manipulate natural systems like this. One would have to be very careful of
not just introducing another pest species, that with all good intentions,
was meant to correct a simple problem, but became a problem in itself. For
example, it is well documented that the high density cultivation of pearls
in semi enclosed lagoons,eg, in a number of atolls in the Cook Islands (mid
Pacific), has resulted in severe deterioration of water quality as a result
of the sheer volume of waste from the biomass of these filter feeding
bivlaves. The pearl shells were not introduced to improve water quality but
it is an example of an introduction of a filtering bivalve that resulted in
changing extremely low nutrient water into very high organic content water.
There may be situations where biological filtering of water to improve its
quality can be achieved, for example, Walter Adey proposed using turf algae
farms to clean up aquarium water that is recycled through a tank. The
results are sometimes not as pronounced or straight forward as the theory
suggests (though enquire at the GBR Aquarium in Townsville, Australia for
more info on a large scale example), and it does require a lot of manual
imput to maintain such a design. So a lot of questions remain as to whether
the water to be 'cleansed' is part of a recycled (or low exchange) system,
or an open, rapid exchange once-use system, then there are all the other
stochastic combinations of factors to take into consideration when
attempting to use any natural system in this manner.

The world is littered with examples of one species being introduced
to address a problem caused by usually extreme anthropogenic disturbances,
only to find you end up with additional problems that are often much more
difficult to fix than the source of the original problem. I suggest that
simple 'fixes' like you suggest should be approached with extreme caution,
nontheless there is a lot literature out there (including from the tropics)
that may be useful to refine your question as to the actual feasibility of
what you want to 'demonstrate' in a pilot project.

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