Tidal Variation in Sediment Densities of Marine Benthic Copepods

Abstract

Recent studies have shown that meiofauna frequently occur in the water column and may be highly mobile due to suspension by water currents or any process that disturbs the sediments. We hypothesized that tidal variability in meiofauna sediment densities and distributions may be significant. As a test of this hypothesis, replicate sediment cores were collected in intertidal, slope (creekbank just below water level), and subtidal muds to determine if densities of benthic copepods varied over a tidal cycle. As determined by analysis of variance, the number of copepods within each area clearly varied with the stage of the tide. In the intertidal and subtidal areas there were significantly more copepods in the sediment at both slack high and low tide than at flooding or ebbing tides. This pattern may be due to resuspension of meiofaunal copepods from the sediment into the water column via tidal current action. At the slope site such a tidal response was more complex and observations on the distribution of certain species in the 3 areas suggest that movement of animals occurred between intertidal and slope areas. All intertidal species did not display the same tidal response, and in the slope and subtidal areas all developmental stages (adults, copepodites, nauplii) did not display the same tidal response. These differences were likely due to differences in the size and/or behavior of adults vs juveniles. The processes which likely act to redistribute mud-meiofauna in many systems have hitherto been largely ignored, yet may have important consequences for the communities.