Effects of fish nests on pattern and zonation of submersed macrophytes in a softwater lake

Nests of centrarchid fishes maintain patches of diaspore-propagated submersed aquatic plants (principally Elatine minima (Nutt.) and lsoetes braunii Dur.) between 0.9 and 2.4 m depth in a softwater oligotrophic lake. Nests are cleared of vegetation in May-June, and abandoned by fish in June. By August, many nests are colonized by diaspore-propa­gated species that do not spread vegetatively on horizontal stems. About 7 5% of the nests are reoccupied by fish the following May, and some new nests are formed. Nests not re­occupied by fish are colonized by rhizomatous plants of 4 species that have not been ob­served to flower or set seed in the lake. Rhizomatous plants reach frequencies near 100% by 14 months after abandonment. Pattern analyses show that patch sizes of diaspore­propagated species correspond to the size of fish nests. Conventional explanations of macrophyte zonation based on depth, exposure, and competition are insufficient in this lake; effects of disturbance must be considered as well.