Research Document - 2007/049
Oceanographic conditions in the Estuary and the Gulf of St. Lawrence during 2006: zooplankton
By Harvey, M. and L. Devine
Zooplankton biomass, abundance, and species composition in the Québec Region (Lower St. Lawrence Estuary [LSLE] and the Gulf of St. Lawrence) during 2006 are reviewed and compared to previous observations (1999–2005). In addition, this report gives an overview of the interannual variability in the mesozooplankton biomass and the macrozooplankton species composition, abundance, and biomass in the LSLE and the northwest Gulf of St. Lawrence (NWGSL) as measured in the fall of each year between 1994 and 2006.
The state of the zooplankton at the three Québec fixed stations in 2006 was estimated as normal (zooplankton biomass, zooplankton total abundance, and copepod total abundance) and above normal (Calanus finmarchicus abundance) at Anticosti Gyre (AG), normal at Gaspé Current (GC), and normal (zooplankton biomass, zooplankton abundance, C. finmarchicus abundance) and lower than normal (copepod abundance) at Shediac Valley (SV). In addition, some changes in the zooplankton community structure were observed over the time series at AG and GC, including some changes in the rank of the top ten taxa and the appearance for the first time of some new taxa in the dominant species (top ten): Temora spp. at GC and echinoderm larvae and larvacea at AG. Likewise, the zooplankton biomass along the seven Québec sections in 2006 was estimated as lower than normal along the Sept-Îles (TSI) and Bonne Bay (TBB) sections, normal along the Lower St. Lawrence Estuary (TESL) and the Centre Gulf of St. Lawrence (TCEN) sections, and above normal along the southwest Anticosti (TASO), Îles-de-la-Madeleine (TIDM), and Cabot Strait (TDC) sections. Concerning the total zooplankton abundance, anomalies were positive for all sections except along the Bonne Bay (TBB) section, where the total abundance of zooplankton was evaluated as normal. In addition, some changes in the zooplankton composition were observed over the time series in each region, including some changes in the rank order of the top ten taxa and the appearance of new taxa in the top ten species: Temora spp. and Oncea sp. in the LSLE; echinoderm larvae, larvacea, and Temora spp. in the NWGSL; and Cladocera in Cabot Strait.
The mean mesozooplankton biomass observed in November 2006 in the LSLE and NWGSL was 1.4 times lower than in 2005 and corresponds to the third lowest value observed over the last 13 years in the study area. Likewise, the mean macrozooplankton biomass decreased from 15.4 in 2005 to 5.9 ww g/m² in 2006; this corresponds to the lowest value observed over the last 13 years. The most notable feature observed in the LSLE and NWGSL was that 2006 had the lowest mean biomass of euphausiids of the last 13 years due to a strong decrease in the abundance of Thysanoessa raschii, which was 4.3 times less abundant in 2006 than over the last 13 years. In addition, the mean abundance of the hyperiid amphipod Themisto libellula estimated in both regions in 2006 corresponds to the lowest value observed over the last 13 years.
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