Zoological Studies

Vol. 47 No. 5, 2008

Taxonomic and Size Structures of Aquatic Macroinvertebrate Assemblages in Different Habitats of Tropical Streams, Costa Rica

Romina E. Principe

La Selva Biological Station, Organization for Tropical Studies, Puerto Viejo de Sarapiquí, Heredia, 41001, Costa Rica

Romina E. Principe (2008) Taxonomic and size structures of macroinvertebrate assemblages associated with different habitats of tropical streams of Costa Rica were analyzed.  Surber samples were taken in riffle and run habitats in 2 streams.  Invertebrates were identified and measured, and the biomass was estimated.  The taxonomic richness and total abundance were higher in riffle habitats.  Correspondence analysis showed a clear separation between riffle and run samples.  The IndVal method identified the characteristic assemblages in each habitat type.  Tricladida, Hydrachnidia, Leptophlebiidae, Hydropsychidae, Simulium sp., Corynoneurini, Orthocladiinae, and Empididae showed significant indicator values for riffle habitats; whereas Bivalvia, Tanypodinae, and Chironomini were the characteristic taxa from runs.  The length-frequency distribution of riffles differed from that in runs in both streams as measured by Kolmogorov-Smirnov tests.  The largest organisms were found in run habitats, with macroinvertebrates belonging to the 1st size class being the most abundant in riffles.  Although larger organisms were found in runs, differences in total biomass between habitats were not observed due to the high number of small invertebrates collected in riffles.  The size spectrum for the entire benthic community showed that the total biomass was relatively equitably distributed among the size classes, although a peak was suggested for medium size classes.  When the size spectrum was separately analyzed in each habitat, a peak was also suggested in riffles.  Differences in the physical attributes of riffles and runs were clearly reflected in the taxonomic composition of the size spectra.  Patterns observed in taxonomic and size structures may indicate different ecological functioning at the habitat level in the tropical streams studied. 

Key words: Benthos, Size spectra, Organism distribution, Community structure, Lotic ecosystem.

*Correspondence: Tel: 54-0358-4676167.  Fax: 54-0358-4676230.   E-mail:rprincipe@exa.unrc.edu.ar