Horizontal transport of marine organisms resulting from interactions between diel vertical migration and tidal currents off the west coast of Vancouver Island

This paper examines horizontal transport of marine organisms resulting from interaction between diel vertical migration (DVM) and numerically generated tidal and buoyancy currents for the southern continental shelf and slope of Vancouver Island, Canada. In particular, we hypothesise that this mechanism is partially responsible for an observed decline in zooplankton biomass on the shelf during spring and summer. We have chosen to operationally test our hypothesis by using the tidal and seasonal buoyancy flows from a three-dimensional baroclinic finite element model to investigate transport resulting from DVM–tidal interactions. This is achieved by statistically comparing the distribution of passive and migrating particles. In this way, we quantitatively show that in summer, nonmigrating particles initially located on the continental shelf tend to be displaced northwestward by the Vancouver Island Coastal Current, while particles undergoing DVM exhibit off-shelf net displacement from June to September.