Modeling particles and pelagic organisms in Chesapeake Bay: Convergent features control plankton distributions

A two-dimensional Lagrangian particle trajectory model is described and use d to study how surface currents transport particles and, by analogy, plankt on in Chesapeake Bay, United States. It is shown that persistent patches of high particle concentration develop in well-defined regions along the east ern shore and in the lower reaches of some western shore tributaries due to a combination of passive accumulation of particles in areas where the flus hing rate is low and convergence. In the model the highest particle concent rations in the Chesapeake consistently develop in the lower bay (latitude 3 7.1 degrees-37.7 degrees N). in two specific regions near the shore of Cape Charles where convergence and downwelling occur. It is shown that one of t hese is associated with a strong and persistent, residual cyclonic eddy loc ated over an abrupt change in bottom topography. Recent bay wide held surve ys reveal that various planktonic groups, including phytoplankton, zooplank ton, and bay anchovy eggs and larvae, have maximum abundances in the vicini ty of this eddy. It is argued that these convergent areas are important fea tures that have a strong influence an plankton distributions and that they provide consistently high food concentrations for higher trophic levels.