Experimental examination of the factors affecting growth and species composition of phytoplankton from Great Salt Lake, Utah


Category:  Ecology
Linked Publication
Language: English
Author(s): Chad Larson
Description: These studies examined the influence of several environmental factors affecting phytoplankton community composition in the Great Salt Lake, Utah. Because many environmental factors can change simultaneously in the field, laboratory experiments were initiated using inoculum from the Great Salt Lake that varied combinations of salinity, water temperature, and nutrient level, while removing environmental stochasticity and grazing by zooplankton. The response of the different taxa (green algae, diatoms, cyanobacteria) in these experiments, as well as that of the' species of green algae.Dunaliella viridis, qualitatively followed trends that have been observed within the Great Salt Lake. Additionally, highest diversity of phytoplankton occurred when primary productivity was low, while highest primary productivity was obtained at intermediate species numbers. Results demonstrate that changing salinity within the Great Salt Lake is a dominant process affecting the diversity of phytoplankton. However, results also highlight the importance of water temperature and nutrient level affecting phytoplankton composition. within the lake. In the same set of experiments, the responses of two measures of diversity, species richness and the Simpson's Index, were examined with changes in the environmental variables. In addition, I found that the highest diversity of phytoplankton occurred when primary productivity was low, while the highest primary productivity was obtained at intermediate species numbers. In a second set of experiments, competition between two important species of green algae was examined across a range of salinities and at different nutrient levels. While D. viridis always dominated, the proportion of total biomass of each species changed with salinity and nutrient level. My results clearly demonstrate that changing salinity within the Great Salt Lake is a dominant process affecting the diversity of phytoplankton. However, results from this study also highlight the fact that water temperature and nutrient level are also influencing phytoplankton composition. While each of these factors is likely, at times, an important determinant of community structure, the composition patterns in the algal community cannot be explained solely in terms of a single factor or process. Community composition is the result of a combination of factors that many times interact.