PHYSICAL AND BIOLOGICAL PROCESSES DETERMINING THE DISTRIBUTION OF ZOOPLANKTON IN A TIDAL ESTUARY

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Abstract
Zooplankton of a small estuary, Great Pond, has been described. It has been shown that in summer there were endemic populations of several zooplankton of which copepod Acartia was most numerous and widespread. Rates at which Acartia must have been replaced to maintain its numbers in surface mixed layer of Great Pond in face of dispersion by tidal exchanges have been calculated. These rates are compared with rates at which Acartia increased or decreased when isolated in bottles immersed in pond. Comparison shows that in most landward parts of pond population in mixed layer could not reproduce fast enough to maintain itself and was dependent on recruitment from deeper layer. In central part of pond reproduction alone was sufficient to offset seaward transport by tidal exchanges. In most seaward parts of pond, mortality was so great that small population was maintained only by transport from landward parts of pond. Comparison reveals contribution of reproduction, growth and mortality and of tidal transport to maintenance of observed distribution of Acartia. Seasonal changes in these physical and biological processes account for seasonal changes in distribution of zooplankton in Great Pond.