Modeling the factors which contribute to zooplankton congregation over Stellwagen Bank

Xuemei Zhai, Harvard University, Cambridge, MA, United States, Glenn Flierl, MIT, Cambridge, MA, United States and James J McCarthy, Harvard Univ, Cambridge, MA, United States
Stellwagen Bank lies at the Massachusetts Bay’s eastern boundary with the Gulf of Maine (GoM) and is encompassed by the Gerry E. Studds Stellwagen Bank National Marine Sanctuary. It is a shoal with primarily sandy bottom and with water depth ranging from 20 meters to 40 meters. The waters all across the bank are highly productive and support large and diverse planktonic and benthic communities, large fish diversity and fish biomass; it is also one of the most active whale feeding grounds in coastal waters of the United States.

Our previous study indicated that several factors might be responsible for the high biomass over and around sea banks and sea mounts in coastal areas: zooplankton diel migration and tidal currents as affected by the topography. Other processes, such as high dissolved inorganic nitrogen (DIN = NH4 + NO3), retention of productivity, plus the advection and local concentration of food produced elsewhere, can also be contributing factors.

In this study, a 2D cross-bank profile model is used to investigate the biological and physical processes that can explain biomass patterns and accumulations across Stellwagen Bank. This study is focused on determining the relative contributions of different factors and processes that are responsible for sustaining high biomass in the Stellwagen Bank ecosystem. The results of this 2D model show that both tidal currents and zooplankton diel migration can independently contribute to the distribution pattern of zooplankton along the Bank. The effect becomes even stronger when these two factors combine. In addition, we found that zooplankton diel migration also affects both phytoplankton and zooplankton biomass, and DIN concentration over the Bank.