Zooplankton of the New York Bight : a comparison of the years 1975 and 1976 during the months of May and June

Abstract

The seasonal abundance and distribution of copepods and other zooplankton in the New York Blight has been described by Judkins, et al. (1980). Their analysis was based on 218 samples collected on 11 cruises over the period of September 1974 through September 1975. We made similar collections with the same gear and at the same station locations during May and June 1976. These last two cruises were made during a widespread bloom of the dinoflagellate Ceratium tripos, which may have contributed to an unprecedented anoxic condition off the New Jersey coast in July and August, 1976. It was felt that an analysis of the May and June 1976 collections, and a comparison with the 1975 data might prove instructive in determining whether the apparently drastic differences in oceanic conditions and phytoplankton populations between the two (1974-5 and 1976) were accompanied by changes in zooplankton abundance and species composition. Coincidental (in time) changes in both trophic levels might be expected through three mechanisms, among others. These are: 1) similar physical forcing such as large scale advection of water masses containing distinct populations, 2) zooplankton population changes induced by the unsuitability of C. tripos as food, or 3) phytoplankton composition changes brought about by selective grazing pressure by anomalous zooplankton populations. Since only pre-anoxic conditions could be addressed, effects of the anoxia itself, and changes immediately preceding the onset of anoxia are outside the scope of this report.