Controls on the vertical distribution of meiobenthos in mud: field and flume studies with juvenile fish

We investigated the influence of the bottom-feeding fish Leiostomus xanthurus Lacépède on the vertical microdistribution of meiobenthos. Sectioned cores which were taken at low tide in the field did not exhibit evidence that fish, which had foraged 3 to 4 h earlier, affected the vertical distribution of meiofauna. However, field cores collected where fish were feeding did show reductions in meiofaunal abundances in the top 2 mm of sediment. Controlled flume experiments also showed that fish influenced the vertical distribution of meiofauna. For copepods, copepod nauplii and foraminiferans, reductions in abundances occurred in the top 4 mm of sediments due to fish consumption and/or migration into the water. For nematodes, reductions in the top 2 mm occurred due to mortality (but not necessarily consumption by fish), as well as possible migration deeper into the sediments when fish were present. In conjunction with this study, we examined the possibility that estimates of total abundance of meiofauna may be influenced by the process of sectioning the cores. We found that total meiofauna abundance was significantly greater in sectioned than in non-sectioned cores, suggesting that investigators must test the effects of sample handling when choosing enumeration methods.