Competition and efficiency in closed freshwater algal systems: tests of ecosystem design principles

Seven species of freshwater algae were grown in defined media in monoalgal and mixed cultures, to test whether species interactions and community efficiency were predictable on the basis of ecological theory. Results supported the prediction of competitive interactions, although no differences were detectable in the strength of competition in two and three species mixed cultures, nor was the severity of competitive effects predictable on the basis of relatedness at the level of phyla. On a community level, cultures with two and three species fixed a greater proportion of available carbon than cultures with only one species, implying a more efficient overall use of available resources. Implications for the design of artificial closed ecosystems are discussed.