Analysis of molecular variation within marine species may reveal much about their population dynamics, including variance in reproductive success, dispersal patterns, and cohort structure and survivorship. The analysis of stock structure of commercially exploited species is one of the foundations for the design of management strategies for sustainable fisheries. Recent studies of molecular variation have revealed significant genetic differentiation among geographic populations (i.e., significant stock structure) of commercially important marine fish, including herring [ Kornfield and Bogdanowicz, 1987], red drum [ Gold and Richardson, 1991], haddock [ Zwanenburg et al., 1992], and plaice [ Stott et al., 1992].
The application of zooplankton genetics to practical problems in fisheries resource management is less clear. For those species that constitute the primary prey species for commercial fishes, knowlege of their population structure, dispersal patterns, and spatial variation in abundance (especially in relation to that of the predator species) may be important in allowing the prediction of the food resource for commercially exploited species. For example, the planktonic copepod, C. finmarchicus, may be transported from multiple source regions to Georges Bank, where it is an important prey species for the larvae of commercial fish, especially cod and haddock. Changes in the mixture of copepods from different source regions from year to year may determine interannual population fluctuations in abundances of the prey species, which may impact the productivity of the commercial fishery on Georges Bank [ U.S. GLOBEC, 1992].
In concert with many other physical and biological processes, the dispersal of important zooplankton species is a determinant of the distribution and rate of secondary production in the ocean. Quantification of dispersal may allow assessment and prediction of spatial patterns of biological production in marine ecosystems. These types of analyses may help move us toward ecosystem-level resource management, as part of a management strategy for sustainable fisheries. Predictive capabilities for the distribution, abundance, and production of organisms at multiple trophic levels may be useful to predict the health and productivity of the ecosystem as a whole. Management strategies that focus on the whole ecosystem will require fundamental understanding of the interconnectedness of biological processes at different trophic levels and the role of physical ocean processes. This same holistic approach will be required to understand and predict how marine ecosystems may respond to climatic and environmental peturbations in the future.
The long-term goal of the population genetic studies of marine organisms is to resolve questions of recruitment dynamics, to understand and predict temporal fluctuations in population size, and to estimate fundamental population parameters (birth, death, immigration, and emigration) for marine populations. Perhaps it may be possible to predict good years and bad years--in terms of yield from a commercially exploited ecosystem--based on these and other assessments. There are, however, limitations to the usefulness of molecular analyses of zooplankton dispersal in the ocean. Genetic analyses may provide statistical and probabilistic understanding of dispersal patterns and pathways of zooplankton at appropriate scales. They are unlikely to provide deterministic answers to questions of dispersal, such as whether the copepods from a particular source region will follow a particular transport pathway and result in a highly productive season for the predator species in a commercially exploited ecosystem.