Seasonal life strategy of Prorocentrum minimum in Chesapeake Bay, USA: Validation of the role of physical transport using a coupled physical–biogeochemical–harmful algal bloom model

Over 40 years ago, it was suggested that Prorocentrum minimum in Chesapeake Bay has a seasonal life strategy that depends on the physical transport by estuarine circulation, bringing cells from lower bay to the mid-bay in spring when they bloom. In this study, a validated hydrodynamic-biogeochemical model is used to simulate the annual cycles of P. minimum in Chesapeake Bay and track its life history over multiple years. The model reproduces the observed seasonal progression of P. minimum without a seed population. Four life stages of P. minimum are faithfully produced in the model: (1) in winter, overwintering populations from the previous bloom are distributed throughout the water column in the lower bay; (2) in late winter/early spring, cells are transported upstream by the landward bottom flows; (3) in May, P. minimum develops a bloom in the mid-bay; (4) in late summer/fall, decaying P. minimum populations are transported downstream by the seaward surface flows. Particle tracking shows that it takes about 3–4 months for the overwintering cells to travel from the lower bay to the mid-bay, but about 6 months for the decaying cells to travel from the mid-bay to the lower bay, as the estuarine circulation is far stronger during the high runoff months of January–May than during the low runoff months of June–December. With the peak growth rate around 20°C, May provides an optimal window of growth opportunity for P. minimum as phytoplankton assemblage transitions from winter–spring diatoms to summer dinoflagellates in a seasonal succession.