Resource dynamics and detritivore production in an acid stream

Abstract

Summary1. Life history patterns and production of eight shredder‐detritivore species were studied in relation to the detritus dynamics of a small acidic stream in England. Mean annual detritus inputs (direct and lateral sources combined) were approximately 400 g m−2 year−1 and showed significant seasonal and annual variation.2. Detritus standing stock did not increase significantly during times of high input, reflecting low retention efficiency. However, the mean detritus standing stock was relatively large (108 g m−2) reflecting a slow decomposition rate typical of acid streams.3. Four species were univoltine with highly synchronous patterns of emergence and recruitment (Leuctra inermis, Leuctra hippopus, Capnia vidua and Amphinemura sulcicollis). Two species were univoltine with extended patterns of emergence and recruitment (Nemoura cinerea, Potamophylax cingulatus). Leuctra nigra was apparently semivoltine, while Protonemura meyeri showed two successive cohorts in the second year of the study, suggesting either bivoltinism or cohort splitting.3. Secondary production of the dominant shredders was 1.67 g m−2 year−1 in 1997 and 1.99 g m−2 year−1 in 1998, which is low compared with other small European streams. This was probably because of an impoverished invertebrate community and poor food quality associated with acid conditions. Food availability probably did not account for the low production as the detritus standing stock far exceeded the estimated shredder ingestion of 42–50 g m−2 year−1.4. Despite low overall shredder production, species‐specific production was high, possibly because of competitive release in this species‐poor acid stream. Periods of high production and growth showed no relationship with detritus availability but were closely related to life history.