Spatial disconnection of plankton dynamics in an Ozark reservoir

This two-year study examined spatial distribution and seasonal population dynamics of algae and zooplankton in Table Rock Lake (Missouri, USA), a large clear reservoir threatened by increased development in the watershed. Regular samples were collected from a polymictic up-lake site (10 m deep, mean Secchi transparency 1.0 m) and a monomictic down-lake site (37 m deep, 4.0 m Secchi) in the productive James River arm. Average abundance and biovolume of most algae groups showed no statistically-discernable difference between these two sites, and maximum cell densities were similar in magnitude (∼ 105 cells/mL). Exceptional were the chlorophytes, which had their highest abundance up-lake. Based on taxonomic composition, both sites appear to be dominated by pelagic algae, with little evidence of riverine immigrants. Algae and zooplankton showed rapid seasonal changes in total densities and composition, and peak abundances showed no association in time between the two sites. Although no floating or suspended colonies were ever visible in the field, cyanobacteria (particularly Oscillatoria) were common at both study sites, and we found numerous genera linked to nuisance blooms in other lakes. Zooplankton communities differed between sites, with cladocerans common in winter and spring at the down-lake site and rotifers common year round at the up-lake site. Important cladoceran grazers, such as Daphnia, were usually not abundant; however, when they were common, algae abundance was always low