Effects of oyster farming service vehicles on an intertidal sand flat

A Tasmanian tidalflat receiving differing amounts of vehicle traffic associated with the servicing of oyster farm leases was sampled for sediment properties and benthic community structure. There was a gradient of vehicle usage in both the littoral zone (LZ) and the intertidal zone (IZ), with the highest usage in the intertidal zone equating to the lowest usage in the littoral zone (IZ2=LZ1). Results indicate that the littoral sediments were less compacted where vehicles were present. Species richness and diversity were reduced in the littoral sites (70%) and one intertidal site (50%) where there was vehicle traffic. Multivariate analyses confirmed the univariate findings. Large bivalves and epibenthic snails were generally less abundant where there was vehicle traffic. However, in the intertidal zone one snail showed the opposite pattern. There was less change in the community structure at sites where vehicles spread out across the foreshore than at sites where all vehicles travelled in a narrow lane, but this reduction in impact was offset by a greater area being affected. This study provides preliminary evidence of a measurable impact on sediment and community composition at 16 vehicle trips per day and suggests that management needs to consider the tradeoff between magnitude of impact and area affected.