Linking pelagic production and sea scallop energy requirement on the Northeast U.S. Shelf: A model-based assessment

Shelf seas often have tight pelagic-benthic coupling through the sinking export of water column production to benthic zone over a small depth range. The amount of energy supply to benthic organisms is controlled by key processes such as the pelagic productivity and sedimentation/resuspension of organic matters. The latter involves bottom boundary layer dynamics and is critical for the coupling, but its importance is difficult to quantify. We use a 3-D coupled biological-physical model to assess the spatio-temporal variability of production exported from the water column to the bottom of the Northeast U.S. Shelf (NES), with a specific attention to the effect of bathymetry, mixing/stratification regime and phytoplankton size composition. We also evaluate the distribution and energy requirement of Atlantic sea scallop (Placopecten magellanicus), an important fishery on the NES. Initial model runs indicated that available phytoplankton near the bottom is not sufficient to meet scallop’s energy requirement, especially on the outer shelf (70-100 m) where the scallops typically reach high abundance. Including detrital organic matter as an additional food source for scallops only partly alleviated the energy deficiency. However, by including a vertical gradient of organic particles within the bottom layer, the energy balance can be mostly reached. An approximation of the vertical gradient was based on the concept of Rouse profile: a concentration profile resulting from the balance of sedimentation and resuspension of particles.