INCORPORATING LOTIC MEIOFAUNA INTO OUR UNDERSTANDING OF FAUNAL TRANSPORT PROCESSES

This work represents the first detailed study using field data and flume experiments to evaluate the magnitude and pattern of meiobenthic drift in a stream, the evidence that both active and passive processes operate during entry and transport, and how meiofaunal transport in streams compares with what is currently known about the transport of lotic macrofauna and of the meiofauna and larval macrofauna of marine systems. Abundances of drifting meiofauna in Goose Creek, Virginia, were extremely high (up to 250,000 per 100 m3) and represented a significant amount of biomass when compared to literature biomass estimates for macrobenthic drift in other warm-water streams. Drift of the dominant taxa in this study (rotifers, early instar chironomids, oligochaetes, copepods) was flow-dependent. Flume experiments examining live and dead entry processes provided evidence that a critical threshold velocity existed (approximately 9-12 cm s-1), above which the number of animals entering the water increased dramatically. This threshold was less than the critical threshold velocity of the streambed substrate (approximately 14-17 cm s-1), suggesting that whenever the streambed is scoured, potentially large numbers of meiofauna may enter the water. Despite the evidence that animals may enter the water passively due to entrainment by flow, active control over drift entry also operated since all four of the dominant taxa exhibited significant increases in drift at night. These diel drift patterns were reflected in reduced streambed abundances at night for chironomids and oligochaetes but not for copepods and rotifers. Additionally, in flume experiments which examined the return of live vs. dead drifting fauna to the bottom, copepods were able to influence their return to the bottom once in transport, a finding consistent with field observations.