Effect of habitat type on benthic macroinvertebrates in two lowland tropical streams, Costa Rica

Benthic macroinvertebrate community structure was studied with respect to s tream habitat type in two lowland tropical streams. Three reaches along the Carbon river and two within the Gandoca stream were chosen as study sites in Talamanca, Costa Rica. Macroinvertebrates were collected from four habit at types: leaf packs in riffles, cobble in rimes, areas of sand in pools, a nd areas of gravel in pools. Communities were dominated by insects in the o rders Ephemeroptera (Thraulodes, Baetis?), Diptera (Chironomidae, Tipulidae ), Trichoptera (Hydropsychidae, Glossosomatidae, Hydroptilidae, Calamocerat idae), and Odonata(Progomphus, Hetaerina). Noninsect macroinvertebrates wer e dominated by shrimps (Macrobrachium) and snails (Gastropoda). Functional feeding group composition was dominated by collector-gatherers. In most rea ches, both habitat types in rimes supported higher macroinvertebrate abunda nce and biomass than did habitats in pools. Leaf packs in rimes represent a n important habitat that is present year-round in these aseasonal tropical systems. Community composition and diversity were similar to that reported for other areas of Central America.