ABSTRACT The annual cycle of distribution and abundance of Calanus finmarchicus on the Northeast continental shelf was animated based on approximately 11,000 Marine Monitoring Assessment and Prediction program (MARMAP) zooplankton samples collected approximately monthly from 1977 to fall 1987. A high degree of temporal and spatial variability in C. finmarchicus abundance throughout the region was evident in our movie.
A distinct annual abundance cycle was present shelf-wide; however, the magnitude and timing of annual maxima varied greatly. The amplitude of the annual cycle was weakest in the Gulf of Maine where high concentrations of C. finmarchicus persisted year-round, and strongest in the tidally mixed shallow water on Georges Bank and inshore Mid-Atlantic Bight, where the lowest densities of C. finmarchicus occurred most of the year. Abundance peaked shelf wide during April when C. finmarchicus was ubiquitously very abundant (>10^4 /10m^2). From September to December, abundance decreased across the shelf and remained high only in the Gulf of Maine. Overall, abundance was lowest in February when numbers ranged from 10^2-10^3/10m^2.
A large part of the spatial and seasonal variation in C. finmarchicus abundance appears to be tightly coupled to major hydrographic regimes and to major circulation patterns on the shelf. There was a sharp distinction between well-mixed Georges Bank and the Gulf of Maine as defined by C. finmarchicus abundance patterns. The presence of consistently high abundance in the Gulf of Maine indicates stable population centers that are a major source of Calanus on the shelf, particularly during March-April. Distributional patterns also suggest an influx of Calanus from Scotian Shelf water in northern Gulf of Maine and on the southern flank of Georges Bank (Meise and OReilly 1996). The distributional patterns along the southern flank of Georges Bank, in Southern New England and the Mid-Atlantic indicate an influx of C. finmarchicus from the shelf-slope front during March and April as well as a resident population (persistent abundance levels of 10^3-10^4/10m^2) in these areas within the 60-100m isobath.
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