Role of habitat in determining macroinvertebrate production in an intermittent-stream system

1. The effect of channel drying on macroinvertebrate production was studied at the habitat and reach scale in a catchment drained by intermittent streams in Maine, U.S.A. The catchment includes two first-order streams and their second-order confluence. Six reaches were selected for study based on differences in channel slope and habitat cover (bedrock, riffle/run, debris dam and pool). Stream water in each reach was acidic and oligotrophic. 2. The study reaches had different degrees of channel drying. In the first-order reaches, surface flow ceased earlier in the season and for longer periods than second-order reaches. Regardless of reach, pool and debris dam habitats retained water longer than riffle/runs and bedrock. Unlike other habitats, debris dams retained moisture for relatively long periods following cessation of surface flow. 3. Reach-specific macroinvertebrate production ranged from approximately 1.7 to 2.9 g AFDM m(-2) year(-1) which are among the lowest values ever reported. Habitat-specific production ranged from approximately 0.5 to 5.0 g AFDM m(-2) year(-1) (bedrock and debris dams, respectively). 4. At the reach scale, quantities of stored benthic organic matter (range approximately 200-600 g AFDM(-2)) decreased in a downstream direction. 5. A combination of differences in the timing and duration of channel drying, habitat structure and detritus standing stocks appeared to influence levels of invertebrate production among the study reaches. 6. Our interpretation of a canonical correspondence analysis indicates that drying is more important than habitat in affecting macroinvertebrate production in this intermittent stream system.