Theses and Dissertations

Defense Date

1993

Document Type

Thesis

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Gary S. Kleppel

Second Advisor

Charles Messing

Third Advisor

D. V. Holliday

Abstract

The purpose of this study was to determine the distributions and abundances of microzooplankton across a front in the Irish Sea, and to test the hypothesis that the structure which develops within the microzooplankton community is the result of the interactions within the communities.

Eight sites were sampled on May 1-2, 1989 along a transect from Liverpool Bay, England to Dundalk Bay, Ireland. The transect crossed both the Liverpool Bay and western Irish Sea fronts; sites were positioned with respect to water type (e.g., coastal, thermally mixed, thermally stratified) . Five sites were sampled by double Longhurst-Hardy Plankton Recorder (LHPR) to determine micro- and macrozooplankton distributions and to identify relationships between these distributions and hydrodynamic and biotic forcing. Microzooplankton samples were microscopically enumerated, and the abundance data processed by Correspondence Analysis to determine interrelationships among the taxa.

Variability in depth-averaged microzooplankton distributions along the transect can be explained largely by the hydrodynamic processes associated with the thermal and density structure of the region. The microzooplankton in the coastal and central channel waters were distinct; the Liverpool Bay and western Irish Sea front apparently act as boundaries between microzooplankton assemblages. The vertical distributions of the microzooplankton at each site appear to be affected by biological interactions between taxa (e.g ., predation).

Correspondence Analysis also identified a sub-surface microzooplankton assemblage off the north coast of Anglesey not associated with strong temperature or density gradients, but which was taxonomically distinct from microzooplankton assemblages at the other locations. A similarity between the microzooplankton assemblages in the surface stratified waters of the western Irish Sea front and the Irish coast (48 km west) was also detected. This suggests the possibility that microzooplankton along the Irish coast have been advected offshore in the coastal waters.

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