Algae-grazing minnows (Campostoma anomalum), piscivorous bass (Micropterus spp.), and the distribution of attached algae in a small prairie-margin stream.

Campostoma anomalum is an algae-grazing minnow, abundant in many streams of the central and eastern United States. In a small stream in south-central Oklahoma, Campostoma has a marked impact on standing crops of attached algae. Pools with schools of Campostoma are barren, while pools in which Campostoma are apparently excluded by bass (Micropterus salmoides or M. punctulatus) support large standing crops of filamentous green algae (predominantly Spirogyra sp. and Rhizoclonium sp.). Campostoma grazed actively on algae-covered cobbles transferred into their pools, and visibly reduced standing crops within one hour. After 24 h of exposure to Campostoma, standing crops of attached algae on cobbles were reduced from 22.0 to 6.3 mg ash-free dry weight cm-2. When a largemouth bass was tethered in a pool with Campostoma, the minnows did not graze on algae-covered cobbles within 30-50 cm of the bass, but fed actively on cobbles that were more than 1.3 m away. These results indicate that interactions of Campostoma and their predators may be an important factor contributing to pool-to-pool variation in attached algae in small streams of the central and eastern United States.