Abstract
Ecological effects should be evaluated at the community-level, considering indirect effects through interspecies interactions. We therefore began to investigate effects of ionizing radiation on microcosms mimicking aquatic microbial communities.
The microcosm used in this study consisted of green algae (Chlorella sp. and Scenedesmus sp.) and blue-green alga (Tolypothrix sp.) as producers; oligochaete (Aeolosoma hemprichi), rotifers (Lecane sp. and Philodina sp.) and ciliate protozoa (Cyclidium glaucoma) as consumers; and four or more species of bacteria as decomposers. The developmental-stage microcosm was acutely irradiated with 60Co gamma-rays at 100, 500, 1000 and 5000 Gy, and population changes were observed over 160 days.
At 100 Gy, all consumers decreased compared with controls, while Tolypothrix sp. increased. At 500 Gy, growth of green algae was inhibited. Lecane sp. decreased compared with controls, and bacteria decreased temporarily. Tolypothrix sp. increased. At 1000 Gy, Scenedesmus sp. and A. hemprichi died out. Growth of Chlorella sp. was inhibited, and bacteria decreased temporarily. Tolypothrix sp., Lecane sp. and C. glaucoma increased. At 5000 Gy, Scenedesmus sp. and all consumers died out. Growth of Chlorella sp. and bacteria was inhibited, while Tolypothrix sp. increased. These effects were not necessarily depended on radiation doses, and some higher population densities were observed in the irradiated microcosm. It is thought that these unexpected results arose from indirect effects. The effects of gamma-rays will be quantitatively compared with those of insecticides, herbicides and copper.
