Zooplankton Communities in the Bristol Channel and Severn Estuary

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Abstract
Zooplankton distributions in the Bristol Channel and Severn Estuary, for Jan., April and Aug. 1974, were analyzed using an hierarchical clustering technique (CLUSTER) and an ordination technique (multi-dimensional scaling). Shade-matrices were used to associate the groups of species with the groups of sampling sites derived from these techniques. Four groups of species or assemblages of zooplankton were described; these were numerically dominated by the calanoid copepods Eurytemora affinis (Poppe), Acartia bifilosa var. inermis Rose, Centropages hamatus (Lilljeborg) and Calanus helgolandicus (Claus), respectively. These 4 assemblages conformed to the generalized classification of plankton according to salinity in estuaries: true estuarine, estuarine and marine, euryhaline marine, and stenohaline marine. The groups were relatively consistent over the 3 mo., chosen to represent the seasonal features of a time series extending from Nov. 1973-Feb. 1975. A strong relationship between the assemblages and salinity was demonstrated. These assemblages conformed to a working definition of a community.