Multivariate analysis of the copepod community of near-shore waters in the western Gulf of Maine

Abundance patterns were described for 15 species of planktonic copepods in coastal waters of the western Gulf of Maine, NW Atlantic, between April 2002 and March 2003. Vertically stratified sampling was carried out at 4 stations along a 12 km cross-shelf transect ranging from 60 m to 105 m depth offshore of Portsmouth, NH, USA. Temporal and spatial patterns of distribution and abundance were described for adult copepods, and multivariate analyses were used to assess trends in community composition. Three species, Oithona similis, Temora longicornis, and Centropages typicus, dominated the community numerically, comprising 72.1 % of all copepods identified. The abundances of 7 species exhibited strong seasonal variation, in contrast to 5 species which were abundant throughout the year. As shown by non-metric multi-dimensional scaling (MDS), the composition of the community changed in a cyclical pattern over the 1 yr period, suggesting a clear seasonal cycle. There was significant vertical partitioning of the copepod community, with significant differences among depth strata at all but the shallowest station. In contrast, significant horizontal spatial variation was evident only in. the deepest stratum; surface and mid-depth samples did not differ among the 4 stations. Although many of the same species found in this study are also known from Georges Bank and Massachusetts Bay, their seasonal patterns of abundance differed notably among the regions. Such dissimilarities emphasize the importance of sampling at appropriate time and space scales in order to accurately assess population and community dynamics of coastal zooplankton assemblages.