COMPARATIVE STUDIES ON ESTUARINE ZOOPLANKTON1

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Abstract
The seasonal cycle of zooplankton in Raritan Bay, New Jersey, was compared with Narragansett Bay, Rhode Island, and the York River, Virginia, to determine the effects of local conditions on latitudinal gradients in species distributions. The dominant copepods in each estuary, Acartia clausi and A. tonsa, alternated cycles of abundance in a similar and predictable manner, and the distribution of Eurytemora spp. reflected the salinity distribution in several embayments. Relative proportions of the major groups comprising the temporary plankton differed significantly between estuaries. Paucity of lamellibranch larvae in the Raritan system probably resulted from organic debris in the water column, whereas the importance of Balanus nauplii in the York River appeared to be the expression of a natural zoogeographie pattern.Local irregularities were noticed in Raritan Bay when A. tonsa disappeared during summer. This highly abnormal situation paralleled drastic fluctuations in the phytoplankton. Lamellibranch veligers and Balanus nauplii increased in numbers where pollution had been reduced. Plant nutrients arising from discharged wastes and land runoff produced fertile conditions for an extremely dense and persistent spring bloom of phytoplankton. The overabundance of food or associated factors may have been responsible for delayed reproduction by Balanus and polychaetes.