Site-to-site variability in abundance of meiobenthic copepods along a tidal gradient over 24 hours

As part of a larger study on the effects of juvenile fish predation on meiobenthic copepods, we collected meiofauna every two hours for 24 hours at three muddy sites along a transect through vegetated marsh, to unvegetated intertidal to unvegetated subtidal habitats. The vegetated marsh (Spartina alterniflora) site harbored significantly more copepods over the combined sampling period than the other two sites. Some species were distributed along the entire transect, but several species were much more abundant at one site than the others. For example, Microarthridion littorale was most abundant at the intertidal site, and Enhydrosoma propinquum was most abundant at the unvegetated sites. The most abundant subtidal species included Pseudobradya pulchella and Paronychocamptus wilsoni. Three species were most abundant in the vegetated marsh (Stenhelia (D.) bifidia, Nannopus palustris, and Diarthrodes aegidius). Maximum total copepod abundance occurred during the daytime low tide at all three sites. Of the four species more abundant in the light than at night, three were subtidal. Most of the time there were no detectable differences between high and low tide abundances, suggesting that there was little exchange of individuals between habitats as tidal levels changed. Without samples from additional transects or the ability to obtain samples for all possible combinations of light and tide levels, we could not detect significant interactions between these two environmental factors. Based upon the species composition of copepods in the gut contents of motile fish predators, the existence of distinct copepod species assemblages at sites along the transect may allow inferences about where fish had fed.Contribution No. 695 from the Bell W. Baruch Institute for Marine Biology and Coastal Research, University of South Carolina.