Algae. 1998; 13(3): 355-360.

Diel Patterns of Phytoplankton and Zooplankton Dynamics in Fish Hatchery Ponds

Jeong Ha Kim, Larry M. O'Flaherty

Department of Biology, Sung Kyun Kwan University. Department of Biological Sciences, Western Illinois University

Diel patterns of phytoplankton and zooplankton dynamics were studied in plastic-line fish hatchery ponds (#3, #4) at the Jake Wolf Memorial Fish Hatchery, Mason County, Illinois, USA. During the 24-hour sampling period, phytoplankton densities inversely coincided with zooplankton densities in both ponds. For the diel pattern, lower densities of phytoplankton were observed in daytime due to differences in densities and composition of the dominant groups of zooplankton, such as cladocerans for Pond 3 and rotifers for Pond 4. In Pond 3, Scenedesmus bijuga was reduced in density by grazing while Cryptomonas erosa increased in density with time due to selective feeding by zooplankton. As expected, dissolved oxygen concentrations were higher in the daytime than at night or early morning. The levels of pH dropped during the same time span and became more basic as temperature decreased and respiration increased with the onset of darkness. Phosphate remained at similar concentrations in both ponds and was not limiting. Nitrate levels were high in Pond 4 due to prior fertilization with liquid inorganic fertilizer.

Keywords : diel variation, food chain, grazing, phytoplankton, population dynamics, water nutrients, zooplankton