Annual Abundances and Growth-Potential of Gymnamoebae in the Hudson Estuary with Comparative Data from the Firth of Clyde

Annual abundances of amoebae in the Hudson estuary were recorded from November, 1992 through November, 1993. Data were analyzed for four morphotypes of amoebae. Minimum numbers of total amoebae were found in winter. Maximum abundances (reaching c. 7,000 l(-1)) occurred in summer, preceded by a rapid increase in the spring. A similar increase in total amoebae during the spring, April through May, occurred also in the Clyde estuary, and reached a maximum of 15,600 cells l(-1) during mid summer. As much as 50 to 60% of amoebae at both sampling sites were less than 10 mu m in length. Hence, smaller amoebae deserve more careful attention in protozooplankton analyses. The two most common morphotypes of amoebae varied inversely in the Clyde estuary during spring; amoebae with extended pseudopodia were replaced by those with flattened or fan-shaped morphologies which dominated into the summer months. Laboratory cultures grown from Hudson water taken in early spring produced a ''bloom'' mimicking that in the natural environment of both the Clyde and Hudson estuaries. This research suggests that seasonal patterns of amoeba abundances are similar in widely separated geographical locations and diverse habitats (i.e. Hudson and Clyde estuaries). The large numbers of amoebae found in this research indicate that amoebae may be more significant in aquatic ecosystems than realized previously.