Changes in environmental conditions and the population dynamics of Calanus finmarchicus in the Labrador Sea (1990-2006)

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A suite of physical, chemical and biological variables are measured at stations along a section across the Labrador Sea between southern Labrador and southern Greenland once a year by scientists from the Bedford Institute of Oceanography. Satellite images of sea surface temperature and chlorophyll provide extended coverage over space and time. From 1990 until 2006 near-surface temperatures increased by about 1°C. Over the same period nitrate concentrations in the central basin increased, while silicate concentrations decreased. Total inorganic carbon concentrations, measured since the mid-1990s, increased and pH decreased. The phytoplankton community appeared to respond to these changes with an overall increase in spring/summer chlorophyll concentrations, but with changes in size/species composition. The zooplankton community did not show large changes in biomass or community composition. On the other hand, for Calanus finmarchicus, which dominates the zooplankton biomass in the central basin, the timing of the appearance of young copepodites was apparently linked to temperature and the timing of the spring bloom. Warmer conditions in late winter were associated with earlier blooms and a higher abundance of young stage C. finmarchicus in late spring. Whether the observed environmental trends are the result of global warming or are part of a normal climatic cycle is unclear. Climate model predictions for the Labrador Sea region are for air and sea temperatures to rise. If this occurs, we expect to see changes in the population dynamics of this most importance component of the zooplankton community