Predominance of picoplankton and nanoplankton in eutrophic Calder Lake

A study was conducted to examine factors regulating the biomass of algal picoplankton in Calder Lake, a small eutrophic lake in southern New York state. A particular focus was a current paradigm which suggests that larger cells may dominate in nutrient-rich waters, while smaller cells may predominate only in oligotrophic waters. Over two years, phytoplankton biomass consisted predominantly (74% on average) of very small organisms, despite the presence of surface blooms of colonial cyanobacteria (Microcystis aeruginosa, Anabaena limnetica ), and dense metalimnetic populations of the dinoflagellate Ceratium hirundinella . This dimictic system is characterized by relatively high levels of total P, inorganic P, and total inorganic N, but larger forms were rarely the most abundant. Greater abundance of algal picoplankton was not associated with deeper strata (low light), or warmer temperatures. Data suggest that midsummer nutrient limitation, especially P-limitation, favors the development of pico- and nanoplankton in the limnetic zone.