Some considerations in the design of aquatic microcosms for plankton Studies

Abstract

Some of the most important problems facing aquatic microcosm research are those resulting from the small size of laboratory microcosms because not all biological and physical processes present in natural ecosystems can be scaled down to laboratory size. Three major problems of scale are: (i) problems arising from the shallow depth of most microcosms; (ii) the difficulty of including higher trophic levels; (iii) the dominance of chemical and biological activity occuring on the sides and bottom of microcosms. The most severe of these problems is the third: in particular, the growth of periphyton on the sides of the container. Periphyton growth exerts a significant effect on the metabolism of microcosms within 40–50 days after inoculation. Biological control of periphyton growth has been largely unsuccessful and the efficacy of mechanical means is uncertain.

A possible resolution of the problem of side activity is to focus on the plankton bloom which occurs shortly after inoculation. Since side growth is not firmly established for almost two months after inoculation, little interference with the activity in the water column is expected. Bloom phenomena in natural systems play an important role in determining the overall behavior of the ecosystem. This viewpoint contrasts with the view of microcosms as progressing toward a state of stability, only then becoming useful as experimental systems.