Field Measurements of Oyster
Filtration: Convenient, Accurate,
and
Useful for Restoration Projects
The recent interest in oyster bed
restoration often has little to do
with increasing harvest of the
delicious bivalves, but is instead
focused on the ability of oysters to
filter phytoplankton and other
particles from the water column.
This filtration function not only
allows for ecologically important
benthic-pelagic coupling, it also
can
improve water quality. Because
filtration capacity is the focus of
so
many restoration projects, it would
be helpful to be able to measure
this parameter quickly,
continuously, and in the field,
rather than
having to bring field-collected
water samples back to the lab, or to
rely on laboratory measurements of
filtration.
A recent study of natural and
restored oyster reefs in South
Carolina
used an in situ fluorometry
technique to gather filtration data,
with
encouraging results. Chlorophyll a
concentrations (a surrogate for
phytoplankton) were measured
upstream and downstream of the reefs
using
both the in situ method and
laboratory analysis of collected
water
samples. Both methods gave similar
results, which indicated significant
phytoplankton removal by the oysters
(a mean of 12.9% removal) in all
but one case (in which onshore wind
likely played a role in resuspending
bottom sediments). Individual
clearance rates averaged 1.21 h-1
for the
small oysters (mean shell height:
36.1 mm) on the intertidal reefs,
which is near the low end of
previously measured laboratory
clearance
rates.
Removal rates were about the same
for natural and constructed reefs,
and
were related more to the size of the
oysters and density of the bivalve
populations on the reefs than to the
age of the reefs. The authors
suggest that these results indicate
that restored shellfish reefs should
be able to bring about water quality
improvements shortly after
construction. The relative impact of
a restored reef will depend on the
size, density, species composition,
location, and flow characteristics
of a given reef. The in situ
filtration measurement technique
used here
should be useful in evaluating
current and future reef restoration
projects.
Source: Grizzle, R. E., J. K.
Greene, and L. D. Coen. 2008. Seston
removal by natural and constructed
intertidal Eastern oyster
(
Crassostrea
virginica) reefs: A
comparison with previous laboratory
studies, and the value of in situ
methods. Estuaries and Coasts 31(DOI
10.1007/s12237-008-9098-8). (View
Abstract:
http://erf.org/cesn/vol31n5r1.html
)
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