COMMUNITY-DEVELOPMENT IN FRESHWATER MICROCOSMS

Two cylindrical freshwater microcosms with a volume of 700 l were maintained under controlled laboratory conditions for 190 days. The two microcosms were identical with regard to initial chemical composition and biological inocula, with the exceptions that in one microcosm (designated Tank 2) mosquitofish (Gambusia) and herbivorous catfish (Plecostomus) were added. Three distinct communities developed in the tanks, a phytoplankton-zooplankton assemblage and two periphyton-zoobenthos communities associated with the sides and bottom of the tanks, respectively. Community development was monitored closely in the zooplankton-phytoplankton assemblage and to a lesser degree in the other 2 communities. Developmental and successional patterns were similar in both tanks. A major difference between the tanks was timing of succession of the zooplankton and zoobenthos, attributable principally to Gambusia predation. One major drawback as a use for an experimental analog such as lakes was the development of a periphyton growth which eventually overwhelmed the biomass of the system. The tanks displayed a degree of successional replicability, a large number of species, and a diversity of community development. Microcosms of this size could find use as experimental systems for higher level trophic manipulation and observation of life cycles not amenable to field studies. © 1979 Dr. W. Junk b.v. Publishers.