We are examining the physical and biological processes which can lead to the formation of high concentrations or swarms. The convergences generated by mesoscale eddies are several orders of magnitude larger than those produced by the mean circulation; however, they are also transient. With an eddy-resolving model, we can estimate the concentration changes for depth-keeping organisms generated by eddy formation and interaction events. The contribution from frontogenesis can also be estimated. Biological processes -- behavior or population dynamics -- can also produce patches. We are using simple predator-prey models to see how trophic interactions producempatchiness and how the mean grazing rates are altered by the spatial inhomogeneities. Finally, we look at how the physical processes, trophic dynamics and behavior can interact and lead to swarms.