Changes in lotic macroinvertebrate communities 8 years after logging were examined in two sets of paired catchments (Sutton and Lewin) in south-western Western Australia by using analysis of variance, classification (TWINSPAN), and ordination (semi-strong hybrid multidimensional scaling). Both paired catchments contained an undisturbed stream and a stream where clearfelling had been taken to the stream edges. The Sutton catchment also contained a stream where clearfelling had occurred but a 100 m-wide strip of vegetation had been retained as a buffer zone. Differences in richness and abundance of animals between the undisturbed and clearfelled streams in the two catchments were obscured by differences between the sites within each stream. However, ordination of the samples revealed differences in the composition of the macroinvertebrate communities between the clearfelled and undisturbed streams in both catchments. Underlying environmental gradients that separated the invertebrate communities in the clearfelled streams from those in the undisturbed streams, in ordination space, were conductivity, the amount of coarse and fine particulate organic matter, and a reduction in total nitrogen. In all, 11 macroinvertebrate taxa were found to be associated with the separation of samples from the undisturbed and clearfelled streams, this response probably being due to increases in conductivity within the clearfelled streams. Macroinvertebrate community structure in the buffered stream was different from that in the undisturbed stream but was more similar to the latter than to that in the clearfelled stream. Physical and chemical parameters of the buffered stream were also more similar to those of the undisturbed stream. These results indicated that the 100 m-wide buffer zone appeared to be effective in ameliorating any disturbance due to clearfelling.
The effects of forestry activities on macroinvertebrate community structure were examined in the
headwaters of Carey Brook in the south-west of Australia. The fauna at four sites on an upland
stream that ran through a logging coupe were compared, before and after clearfelling, with the
fauna at four nearby undisturbed sites. Mean species richness and mean total abundance declined
at the treatment sites relative to the control sites after the commencement of clearfelling activities.
The composition of the macroinvertebrate fauna in the disturbed stream changed in comparison
with that in the undisturbed sites after logging started but returned to the pre-logging composition
after winter and spring rains had stopped. The observed changes in the macroinvertebrate fauna
occurred during the periods of high loads of suspended inorganic solids at the treatment sites.
The possible reasons for the observed results are discussed.
Parastacoides tasmanicus tasmanicus, which burrows extensively into the peat soils of south-western Tasmania, is, like most freshwater crayfish, an omnivore. All food categories in the diet vary seasonally. Detritus, including unidentifiable material, is the major food type present in the gut contents, although root and algal material are also important. Less animal material is present in the diet than in the diet of open-water species, and the taxa consumed and size of prey differ between the adults and juveniles. Cannibalism occurred in less than 1% of the crayfish examined, an incidence considerably lower than that reported for any other crayfish species. Animal material was of comparatively little importance, but the low levels of mineral nutrients, bacteria and fungi in peat soils probably increase its importance as a protein source. The burrows of P. t. tasmanicus include blind, root-lined chambers beneath clumps of sedgeland plants. Larger animals occupy larger burrows and these have a higher proportion of their volume in the form of blind chambers. The animal appears to spend the majority of its time foraging within its burrow system, a behaviour that contrasts with most other crayfish.
The efficiency of a modified Boulton suction sampler was tested in 2 riffle zones, using multiple
removals. Macroinvertebrate fauna was sampled with approximately 70% efficiency on first removal,
while organic matter was sampled with 55% efficiency. Sampling efficiencies for specific taxa ranged
from 86% (Plecoptera) to 66% (Chironomidae) and 59% (Trichoptera). The results of this study
indicate that sampling efficiency can be improved either by taking multiple samples at one location
or by increasing the time spent disturbing the substratum and pumping water from the stand pipe.
The results also indicate the importance of conducting pilot studies to determine the efficiency of a
sampler at sites where the efficiency is likely to be different.
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