The effects of shade and light on Spirogyra and Cocconeis densities in an artificial environment.

Abstract

The growths and abundances of photosynthesizing algae in aquatic systems are essential components of the food chain. Small changes in environmental factors such as light, temperature, and salinity can cause dramatic reductions or blooms in algal communities. I analyzed the growths of two genera of algae, Spirogyra and Cocconeis, under different levels of light, created with shade cloth, in a controlled laboratory setting. Densities of Spirogyra decreased with increasing levels of light. Cocconeis did not survive in any of the light treatments. Instead, Tetraspora, Ankistrodesmus, and Scenedesmus dominated, each decreasing in density with increasing levels of light. These results did not support the hypothesis that light limited photosynthesizing algae would grow more effectively at high light levels than low light levels. The light treatments in fact, may have been substantially higher than what is optimal for each algae. Thus, other factors, such as photoinhibition, UV light, and temperature must be accounted for.