Research Document - 2004/033
Biological and Chemical Oceanographic conditions on the Newfoundland Shelf during 2003
By Pepin, P., G.L. Maillet, S. Fraser, D. Lane
We review the information concerning the seasonal and interannual variations in the concentrations of chlorophyll a, major nutrients, as well as the abundance of major taxa of phytoplankton and zooplankton measured from Station 27 and along standard transects of the Atlantic Zone Monitoring Program in 2003. The vertical attenuation coefficient at Station 27 was consistent with previous observations but was reduced relative to the Spring Bloom in 2002. Water column stability was weaker than in previous pervious, a trend consistent across most of the Newfoundland Shelf. The reduction in the upper and lower water column inventories of the major limiting nutrients at Station 27 observed in earlier years, continued to decline in 2003. This trend was not apparent along the seasonal section occupations. The magnitude and duration of the Spring Bloom at Station 27 in 2003 was comparable with previous years, a pattern confirmed for the Avalon Channel using SeaWiFS remote sensing data. The cell densities of major taxanomic groups of phytoplankton consisting of Diatoms, Dinoflagellates and Flagellates declined in 2003, continuing a trend noted since 2000. This decline may be the result of a change in collection methodology and is currently being evaluated. Overall, phytoplankton biomass on the Newfoundland and Labrador Shelves was lower in 2003 relative to the average of 2000-02.
In 2003, the overall abundance of zooplankton at Station 27 was comparable to previous years. The relative abundance of cold water (Calanus glacialis, C. melgolandicus, Microcalanus sp.) and warm water species (Temora longicornis) appeared to have returned to conditions found in the late 90s after showing a shift toward cold water species in recent years. The most notable changes in zooplankton community during the spring and summer of 2003 involved the lower abundance of large calanoid nauplii throughout the region (˜33-50% of average) and the near absence of Aglantha digitalea (˜10-30% of average). With respect to other changes, the Newfoundland-Labrador shelf boundaries appeared to delineate areas of change. In the southern region, larvaceans were substantially lower than the previous years' average (˜50%) whereas abundance in the northern region we slightly above normal. On the Labrador shelf, species of Oncea, Calanus and Metridia were generally 2-3 times more abundant than the average for previous years.
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