Wendy Gentleman, Daniel Lynch, Dennis McGillicuddy, Cabell Davis
Recent analysis of the MARMAP data for the copepod Calanus finmarchicus has shown a high degree of seasonal and spatial variability in the mean abundance and a low intraseasonal/interannual variance in regions of high mean abundance. This suggests the presence of stable regulatory mechanisms that dominate the seasonal transitions in abundance. The present work examines the extent to which the interaction of climatological transport and population dynamics are responsible for these changes. The approach taken is to couple stage-based population dynamics and realistic seasonal circulation.The current focus is the period from January-February to March-April. Two behavioral scenarios in terms of vertical distribution are investigated: i) homogeneous distribution throughout the water column; and ii) homogeneous distribution in the top 25 meters. The model is initialized with the historical data for January-February and the results of 60 day simulations are then compared with the data for March-April.
These comparisons reveal that, while the southern flank of Georges Bank will be affected by inputs from the Scotian Shelf and Slope waters (data for which are not in MARMAP), the Gulf of Maine supply to the Georges Bank is unaffected by these source regions during the course of 60 days. The Gulf of Maine January-February abundances are sufficient to provide increases seen on Georges Bank and, in fact, significant mortality must occur en route to the bank. Food limitation is a credible hypothesis for source of this mortality. Assumptions of behavior (both in terms of vertical distribution and response to food) are essential as they have a large effect on the resulting distribution pattern due to the faster surface water flows, upwelling and downwelling in the top 25m and the spatial variation in available food.
Zone of 60-day influence of boundary conditions. Regions in dark blue are where direct comparison to data may be made without additional assumptions for Scotian Shelf or Slope water contributions.
Results of 60 day passive transport (no mortality of fold-up of lower stages) of adults. Results shown are plotted as the log transform (log10(x+1)) of the vertically integrated abundance.
Results of transport and 13 stage 'best case scenario' (no mortality, no effect of food, temperature dependent development rates) population dynamics for 60 days. Initial Conditions included no naupliiar stages. Results shown are plotted as the log transform (log10(x+1)) of the vertically integrated total abundance for stages C3-C6.
Results of transport and 13 stage first-order approximation to food-limition (mortality rates vary with Chl-a concentration and temperature dependent development rates) population dynamics for 60 days. Initial Conditions included no naupliiar stages. Results shown are plotted as the log transform (log10(x+1)) of the vertically integrated total abundance for stages C3-C6.
