Community Gradients in the Scotian Shelf Zooplankton

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Abstract
The structure of the zooplankton community of the Scotian Shelf was investigated during eight cruises between August 1978 and September 1980. An inshore–offshore community gradient correlated with temperature, salinity, and distance to shore was the strongest pattern revealed by reciprocal averaging. Zooplankton taxa were grouped as inshore (characterized by Arctic species), intermediate (the dominant shelf species), or offshore (expatriate species) on the basis of reciprocal averaging results and correlations with environmental variables. Recurrent group analysis revealed a pattern consistent with that of reciprocal averaging. A shelf recurrent group was always present, dominated by the "core" species: Calanus finmarchicus, Metridia lucens, Pseudocalanus minutus, Oithona similis, and Limacina retroversa; related shelf edge/slope groups were also present. Substantial differences between cruises were apparent in both reciprocal averaging and recurrent group analysis results and appeared to be related to aperiodic changes in hydrographic conditions. Aperiodic incursions of slope water may represent an energy supplement (as nutrients or zooplankton prey species) or an energy loss if expatriate species exploit the shelf community.