Plankton patchiness: biology in the physical vernacular

Using examples drawn primarily from productive continental shelf systems (the southern British Columbia coast and the North Sea) we describe some important features of the horizontal patchiness of phytoplankton and zooplankton biomass and community patterns. At least in these systems, the intensity, morphology, and scale dependence of the plankton spatial pattern are strongly regulated by and spatially correlated with physical oceanographic processes (turbulent advection, upwelling, convergence, and vertical mixing) and the interaction of these processes with bathymetry. Although frequently considered in theoretical studies, purely biological forcing mechanisms such as predator-prey oscillations do not appear to be as important as biological–physical interactions. The development and persistence of biological spatial pattern in the ocean is dependent on the existence of spatial gradients in the local rate of population increase or decrease. The approximate proportionality between spatial extent and temporal persistence of physical features in the ocean provides a basis for estimating the relative effectiveness of the biological rates (competition coefficients, population growth rates, motility) responsible for patch generation.