Small-scale temporal variability in assemblages of larval fishes: implications for sampling

Short-term changes in the assemblages of larval fishes in waters over the inner continental shelf off Sydney (Australia) were examined.This was done to highlight the potential sampling problem of confounding short-term variability with longer-term and spatial variability in plankton communities. Assemblages at the surface and at 30 m depth were sampled twice a day over consecutive days at two locations 5 km apart. The assemblages and the densities of individual taxa varied greatly between sampling times and days. The small-scale temporal changes in densities of larvae were not the same at both locations or between depths. Large and consistent depth-related differences in assemblages and abundances of most taxa were evident. The consequences of small-scale temporal variations are discussed relative to the design of sampling programs for ecological and environmental purposes. Studies that include the double sampling of some stations are recommended. Greater emphasis needs to be placed on fine-scale oceanography and larval behaviour to determine causative mechanisms of short-term changes in assemblages of larval fishes.