Zooplankton Communities in the Bristol Channel and Severn Estuary

Abstract

Zooplankton distributions in the Bristol Channel and Severn Estuary, for January, April and August 1974, were analysed 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 aMnis (Poppe), Acartia bifilosa var. inermis Rose, Centropages hamatus (Lilljeborg) and Calanus helgolandicus (Claus), respectively. These 4 assemblages conformed to the generalised 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 November 1973 to February 1975. A strong relationship between the assemblages and salinity was demonstrated. It is suggested that these assemblages conformed to a working definition of a community.