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Scotian Shelf Associated Investigators: Related Web Sites: Related Time Series: Zooplankton are sampled every 2-4 weeks at Station 2 of the Halifax Line (HL2), which is 150 m deep and located approximately 12 kilometres offshore from Halifax on the inshore edge of Emerald Basin. Vertical tows are made from near-bottom to surface using a ringnet (0.75 m diameter, 200 µm mesh). Research ships, trawlers, and small vessels are used as sampling platforms. CTD profiles are recorded, and water samples are collected in Niskin bottles for the measurement of phytoplankton, nutrients, and extracted chlorophyll. Chlorophyll and nutrient concentrations are measured for individual depths, whereas subsamples from each depth are combined to give an integrated sample for phytoplankton cell counting. Zooplankton samples are split, and one-half is used for wet-dry weight determination. The other half is subsampled for taxonomic identification and enumeration. Biomass of the dominant groups is calculated using dry weights and abundance data for various groupings (Calanus, by species and stage, Oithona, Pseudocalanus, and Metridia). The data are entered into the BioChem database at the DFO. An ecosystem status report on the state of phytoplankton and zooplankton in Canadian Atlantic waters is prepared every year. Monthly average abundance of total copepods is very variable at HL2, but shows minima in February and September. Annual average abundance anomalies were highest in 1999 and 2000, and lowest in 2002 and 2007, suggesting an overall downward trend. In addition to copepod abundance, co-sampled time-series of total zooplankton wet weight, integrated chlorophyll, and integrated temperature data were available for the site (Standard Co-sampled Variables Plot), together with Reynolds SST. Although the seasonal cycles of copepod abundance and total wet weight are similar, the annual anomalies of total wet weight differ slightly as a result of the influence of phytoplankton blooms in the measurement. Chlorophyll concentrations demonstrate a seasonal cycle similar to that of the copepods. Like Prince 5, the annual chlorophyll concentrations demonstrate a slight downward trend over time, thought to be caused by a decline in Diatom abundance (Li et al., 2006). At-site sampled integrated temperature and Reynolds SST demonstrate similar interannual increases and decreases, but differ slightly in their seasonal cycles, most probably attributable to the larger spatial region represented by the Reynolds data. The CPR standard area closest to HL2 is E10 . Copepod abundance from the CPR corresponds neatly with the HL2 copepod abundance (Standard Long-term Comparison Plot), whereas differences between CPR copepod abundance and HL2 wet weight are probably caused by contamination with phytoplankton in the wet mass measurement. The SST values are at the high end of an approximately 50-year, multidecadal trend (Standard Long-term Comparison Plot). In general, water temperature is often correlated with the state of the North Atlantic Oscillation (NAO). At this time, any relationship between water temperature and zooplankton abundance is inconclusive. REFERENCES: Li, W. K. W., Harrison, W. G., and Head, E. J. H. 2006. Multiyear trends in plankton show coherent sign switching. Science, 311: 1157-1160. |