SHORT-TERM TEMPORAL VARIATION IN COASTAL ZOOPLANKTON COMMUNITIES - THE RELATIVE IMPORTANCE OF PHYSICAL AND BIOLOGICAL MECHANISMS

Drogues were deployed off the coast of Northumberland (north-east Engl and), as they were tracked zooplankton were collected, by four vertica l hauls of a UNESCO WP-2 net (200 mu m), adjacent to the drogue at hou rly intervals. Sampling covered a full tidal cycle, at least once each month from February to April, and in July and August 1993. Short-term changes in the community structure (in terms of species composition a nd abundance) were investigated with respect to the local wind field a nd tidal advection. It was observed, from a cluster analysis, that dur ing horizontal transport, the zooplankton maintained the same communit y structure for at least three consecutive hours on each sampling occa sion [Pearson correlation (r) greater than or equal to 0.70; P < 0.01] even during periods of high turbulent mixing, driven by wind stress. Multiple regression models including parameters of the wind field and the rate of horizontal transport only accounted for a maximum of 52% o f the temporal variation in zooplankton community structure. The unacc ounted for variation provides the basis for the consideration of the z ooplankton as active drifters' rather than 'passive particles', this i s discussed.