Comparative Population Dynamics of Freshwater Dinoflagellates of the Genera Peridinium and Peridiniopsis

Canion, Andy (2004) Comparative Population Dynamics of Freshwater Dinoflagellates of the Genera Peridinium and Peridiniopsis. Undergraduate thesis, under the direction of Clifford Ochs from Biology, The University of Mississippi.

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Abstract

Freshwater dinoflagellates, like their marine relatives, have the potential to reach large population sizes known as blooms. Though they are not toxic like some marine forms, freshwater blooms may have a large impact in their respective ecosystem. This study investigated the temporal and spatial changes in population density of four Peridinium species (P. deflandrei, P. volzii, P. wisconsinense, and P. limbatum) and one Peridiniopsis species (Peridiniopsis polonicium) in Boondoggle Lake, a shallow lake (4.5 m) in northern Mississippi (Lafayette Co.). On each sampling date, measurements of the abiotic environment were made, including dissolved oxygen, temperature, pH, and turbidity. Also, water samples were taken from three depths: 0.25 m, 1 m, and 2 m. Estimates of total dinoflagellate density were made by enumeration of concentrated samples on LM slides. Individual species were identified using SEM, and estimates of the relative abundance of each species were made at the SEM, which allowed estimates of the actual densities of each species to be made. One species, P. deflandrei, was by far the most dominant in the summer bloom (90% of the total dinoflagellate population) and reached a maximum population density of 2.75 X 10^5 cells/ L. P. volzii was the most abundant species in the spring and late fall, with its maximum density being 5.7 X 10^4 cells/ L. The other three species had temporal patterns similar to either P. deflandrei or P. volzii but never comprised more than 25% of the total dinoflagellate population. P. limbatum reached maximum densities in the spring and fall, similar to P. volzii. P. wisconsinense and Peridiniopsis polonicium reached maximum densities in the summer, similar to P. deflandrei. The species composition and population density of dinoflagellates in Boondoggle Lake are determined by many environmental factors. Those that are likely to be most important include low nutrient levels, an acidic pH (5.5-6.5), warm temperatures, summer anoxia, wind protection, and interspecific competition.

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