There are several common threads in the studies that have been summarized above. The zooplankton species studied exhibited molecular diversities in the average range, despite enormous census population sizes and geographic distributions. This result is contrary to theoretical predictions of high genetic diversity in large populations.
Many species have one predominant, nearly ubiquitous haplotype and numerous unique ones.
Populations may be delimited by gradual changes in the frequencies of genetic characters rather than by abrupt changes in the genetic makeup of the population. Exceptions to this principle are cases of subspecies or cryptic species, between which there may be sharp genetically-defined boundaries. The most probable explanation is that ocean mixing is usually sufficiently frequent and effective to obscure boundaries. Molecular population genetic analyses of zooplankton have practical applications in the prediction of spatial and temporal patterns of secondary production in marine ecosystems. The long-term goal of these studies is to understand the biological and physical determinants of the productivity of marine ecosystems, especially those that are commercially exploited.