Research Document - 2003/077

Oceanographic conditions in the Estuary and the Gulf of St. Lawrence during 2002 : zooplankton

By Harvey, M., St-Pierre, J-F., Gagné, A.,
Beaulieu, M-F. and Gagnon, Y.

Abstract

Zooplankton biomass, abundance, and species composition in the Québec region (Lower St.Lawrence Estuary and Gulf of St. Lawrence) during 2002 are reviewed and related to conditions during the preceding year and over the longer-term where applicable. In addition, this report gives an overview of the interannual variability of the mesozooplankton biomass and the macrozooplankton species composition, abundance, and biomass in the Lower Estuary and the northwest Gulf of St. Lawrence as measured in September in each year between 1994 and 2002.

The zooplankton biomass and abundance in the Québec fixed stations in 2002 were comparable to conditions observed in previous years except in the Gaspé current were the mean integrated zooplankton biomass was 1.5 times higher in 2002 than in 2001 and 2000. Copepod eggs, juveniles, and adults were clearly dominant, accounting for more than 80% of the zooplankton community for all sampling dates in the Anticosti Gyre and the Gaspé Current. The depthintegrated abundance of the stage composition of Calanus finmarchicus showed that in 2002 there was two periods of reproduction for this species in both stations. The first and the second period of reproduction occurred in summer (June-July) and fall (September-October) respectively and were synchronized in both stations. The same situation was observed in 2001 and 2000.

The zooplankton biomasses observed in spring and fall 2002 along the six AZMP sections were comparable with observations made in 2001 and 2000. The zooplankton abundance was higher than in 2001 in both the LSLE and the Gulf of St. Lawrence but comparable to the levels observed in 2000.

The mesozooplankton biomass in the Lower Estuary and the northwest Gulf of St. Lawrence in 2002 was slightly higher than in 2001 while the macrozooplankton biomass was comparable to the level of 2001. The year 2002 was characterized by a significant increase of the mean abundance the chaetognath Sagitta elegans, the gelatinous zooplankton Aglantha digitale, Obelia sp., and Boreo sp., and the pelagic amphipod Themisto abyssorum and a significant decrease of the mean abundance of the mysid Boreomysis arctica

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