Oneida Lake: Long-term Dynamics of a Managed Ecosystem and Its Fishery
Chapter 11: Zooplankton in Oneida Lake: Population Dynamics, Trophic Interactions, and Dormant Egg Bank
Carla E. Cáceres, Nelson G. Hairston, Jr., Lars. G. Rudstam, Edward L. Mills, Tom O’Keefe, Lori A. Davias, Christopher Hotaling, and Laura E. Jones
Planktonic assemblages are often used to examine general issues in population and community ecology. Estimates of abundance, biomass, and productivity are easily obtained, while the short life-span and small size of the organisms facilitate experimental and observational studies. Consequently, considerable evidence has accumulated that demonstrates the contribution of both biotic and abiotic factors to the population dynamics and community structure of the pelagic zone. In many lakes, these factors are consistent enough to result in a repeatable pattern of seasonal species replacement (Sommer et al. 1986, 2012). For example, there is often an annual progression of phytoplankton from a spring bloom of edible species, followed by a clear water phase characterized by low phytoplankton abundance, and then a summer increase in inedible algae. Large-bodied zooplankton often dominate the plankton in early spring, with peak densities occurring during the clear water phase, whereas summer plankton assemblages are often dominated by smaller-bodied forms that are better able to cope with late summer phytoplankton, less vulnerable to predation by fish, or both. Fall assemblages often see an increase in large algae and zooplankton.
Despite the predictability in the general patterns, considerable annual and inter-annual variation in population dynamics and community interactions remains unexplained (Kratz et al. 1987; Cottenie 2005). The timing of the clear water phase may vary considerably among years. A previously rare species may suddenly displace the dominant one. The abundance of a certain taxon may remain low despite minimal predation or grazing and high resource levels. Species that do not normally co-exist may be abundant throughout a particular season. Examples such as these are in part due to rare phenomena and time lags that may not be observable at the time scale of a typical research grant or graduate student thesis. Long-term data sets are therefore invaluable resources for gaining a more thorough understanding of the mechanisms that shape ecological patterns.