Effects of shrimp on periphyton and sediments in Atlantic forest streams: an exclusion experiment

VISONI¹, S. B. C. & MOULTON¹, T. P.

¹ Departamento de Ecologia - IBRAG - Universidade do Estado do Rio de Janeiro - Rua São Francisco Xavier, 524 - Rio de Janeiro, RJ, Brasil - CEP 20550-011 - email: moulton@uerj.br.

ABSTRACT: Recent studies have shown various cases in which shrimp and fish detritivores strongly influence the benthic community of Neotropical streams. We studied the effects of atyid (Potimirim glabra) and palaemonid (Macrobrachium olfersi) shrimp in two fishless third-order forest streams at Ilha Grande, RJ, Brazil. We used cages to exclude shrimp from stones and mesh substrate and compared the deposition of sediments and growth of algae (chlorophyll-a) with substrates in open cages and without cages. After 6 and 24 days, stones protected from shrimp inside closed cages had more sediment than those in open cages and without cages. Chlorophylla on stones did not significantly vary with experimental treatment, but mesh substrates developed less chlorophyll-a in the absence of shrimps than in the other treatments. We hypothesize that either increased sediments inhibit periphyton growth or that, in the absence of shrimp, ephemeropteran grazers are more active. We conclude that atyid shrimps significantly remove sediments in the pools and slow-current sites.

Key-words: ecosystem engineering, strong interactors, sediments, periphyton, benthic community, stream ecology.