Exoenzyme activity associated with lotic epilithon

SUMMARY. 1. Epilithic communities were developed on glass slides under four regimes of relative current velocity and light exposure, designated as slow‐light, slow‐dark, fast‐light and fast‐dark, in a fourth‐order boreal stream. Ten samples were collected over an 8‐month period and analysed for biomass, chlorophyll and exoenzyme activity. Fourteen assays were used to monitor the activity of eleven types of exoenzymes involved in the degradation of cellulose, lignin, chitin, xylan, protein, glycogen, organic phosphates and organic sulphates.2. The communities that developed under each current and light regime were distinct in structure and species composition, but had similar patterns of exoenzyme activity. Overall, exoenzyme activity was closely correlated with biomass. The most readily detected enzymes were phenol oxidase, phosphatase, alpha‐1, 4‐glucosidase, beta‐1, 4‐N‐acetylglucosamidase, and beta‐1, 4‐glucosidase.3. Calculating exoenzyme activities per unit biomass eliminated the covariance between biomass and enzyme activity, revealing quantitative differences in exoenzyme activity among communities. The highest exoenzyme activity was associated with the slow‐dark epilithon and the least with the slow‐light. Fast‐light and fast‐dark were intermediate.4. Biomass, chlorophyll and exoenzyme activity showed marked seasonal variations. In general, carbohydrases and the phenol oxidases had different seasonal activity patterns with carbohydrase activity peaking in the summer and phenol oxidase activity increasing markedly in the autumn.5. Differences among epithilic communities could not be readily accounted for by single factors. Community development was determined by the interactions among current, light, macroinvertebrates and season.