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may be considerable natural changes in
the density and distribution of benthic
organisms (Hartley and Dicks, 1987), and
the two sites I chose to examine in
Cowichan Bay did vary, both in numbers of
organisms and in types of dominant
species. To relate cause to effect, it is
important that natural variables such as
sediment type, organic content, water
depth, currents, salinity and temperature
are recorded and taken into account in
the interpretation of results (Hartley
and Dicks, 1987). I found temperature,
salinity and depth to be the same in both
areas, indicating that these variables
are likely not the cause of variation at
this time. Sediment type did, however,
vary between the two sites, showing this
as a plausible cause. Some natural
variation in sediment was expected due to
the location of the two sites. Site 1,
being farther in the estuary would
naturally consist of more muddy type
sediment while site 2, which was farther
out in the bay, would tend to be more
sandy. This would not, however, explain
the much higher percentage of wood debris
in site 1. Both my testing and the
science camp testing showed wood debris
to make up a large part of the substrate
of site 1 but not site 2, suggesting this
to a likely cause of benthos differrences
between the two sites. Studies by Conlan
and Ellis (1979), have demonstrated that
wood waste had an effect on both the
nature of a benthic community, and on
numbers of individuals. Deposition of
more than a 1 cm layer of wood waste was
associated with noticeable losses of
suspension feeding polychaetes and
bivalves, and that the losses increased
progressively with amount of waste
deposited. This concurs with my results
in that clams were much more abundant in
site 2, where wood debris was at a much
lower level. Like in Conlan and Ellis'
study, despite the numerous infauna found
populating the debris bed, the community
was reduced in biomass and had lost much
of the suspension feeding component which
dominated the sand bed community. Possible errors
include the fact that some worms counted
as individuals may have actually been
segments of worms broken in the sieving
process. It is also important to consider
that animals smaller than 1mm would have
escaped through the bottom sieve and that
fast moving animals, such as larger
crustaceans, would have the chance to
escape the grab.
As I
only assessed one set of samples, it is
impossible to make any definite
conclusions as to the absolute variation
of these two sites. The numerical
composition of a macrobenthic community
may change with time (both seasonally and
from year to year) and these variations
must either be measured or avoided as far
as possible, if the task of detecting
pollution effects is to be simplified
(Hartley and Dicks, 1987). Therefore,
further and more extensive sampling
(including elements such as water quality
testing and organic analysis of the
sediment) would have to be conducted in
order to determine the magnitude of the
effect of log handling on the benthic
community in Cowichan Bay. Also, a grab
which could access a deeper layer of
sediment could be useful to compare the
sediment type and benthos beneath the
surface layer. However, there is no
question that at the time of my study,
there was noticeable low diversity and
biomass at site 1 relative to site 2. The
effects of such a low biomass may
significantly reduce the productivity of
this part of the estuary in the long run,
especially in terms of fish since benthic
invertebrates provides much of the food
source for fish in the area (Bell and
Kallman, 1975). The importance of the
benthic community has far reaching
impacts upon the estuary and its other
inhabitants, making the monitoring of
this community a necessity if we wish to
evaluate the "health" of the
estuarine environment.
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