Patchy distribution of zooplankton: Behavior, population assessment and sampling problems

Zooplankton and micronekton are often highly aggregated. Density in aggregations can reach 100 to more than 1000 times the average density of the population as estimated by net sampling. In order to assess true abundance of the animals and understand the significance of the aggregations, more information is needed on the behavior and population ecology of individual species and the species-specific attributes of discrete assemblages. We present information on patterns of intense aggregations of protozoans, platyhelminthes, scyphomedusae, copepods, mysids, and sergestids from our own observations. Characteristics behaviors of different species include feeding swarms of Noctiluca miliaris, behaviorally maintained swarms of planktonic flatworms, diel horizontal migration of Mastigias sp. swarms, three patterns of copepod swarms, bathymetric zonation of mysid schools, and seasonal migration and near bottom swarming of Sergia lucens. After the principles were demonstrated, we consider how to relate sampling, behavior, and population dynamics. We stress that the methodology is the result of the question, not the other way round. To tackle the problems associated with “behavior” in the open ocean, which we did not observe from the surface, it is necessary to sample in more than one way to extract data on differences in population-specific biology that alternative methods supply.