The role of aeglids in shredding organic matter in neotropical streams

Abstract

We studied the input of allochthonous plant material in Crab Creek, a first-order Neotropical stream and its processing by Aegla longirostri Bond-Buckup and Buckup, 1994, a crustacean shredder. Three experiments were performed: (1) to evaluate the input of allochthonous organic material, five suspended and ten lateral collectors were installed. The yearly input of litter was 1254 g m−2 year−1, with no difference among the seasons of the year. (2) To evaluate the importance of A. longirostri for litter shredding, two types of experimental channels were placed in the stream, both containing litter bags with leaves of Ficus luschnathiana; open channels which allowed individuals of A. longirostri to access the leaves, and channels that were closed with a 5-mm mesh to exclude the crustaceans. The leaves decomposed more rapidly in the presence of aeglids (one-way ANOVA; F = 10 . 1795 ; P = 0 . 0005 ), indicating their potential role as shredders. In addition to accelerating the decomposition rate, the presence of A. longirostri altered the community composition and density of the other macroinvertebrates associated with the litter bags. (3) To evaluate the proportion of leaf input that A. longirostri was able to process, a laboratory experiment was performed. Leaves of Cabralea canjerana, F. luschnathiana, and Nectandra megapotamica, which are common species in the vicinity of the study site, were placed in litter bags and incubated in the stream for 20 days. These leaves were offered to the aeglids, and their consumption was recorded. Leaf consumption did not differ between adult (males and females), but did differ between adults and the juveniles (one-way ANOVA; F = 4 . 1633 ; P = 0 . 0279 ). These data indicated that the adult population of A. longirostri is able to process approximately 5% of the leaves that fall in the creek. These results indicate that Crab Creek receives different types of plant material that will be accessed by the aquatic community. These locations may show a scarcity of insect shredders, with crustaceans, especially aeglids, assuming this role in the community.