Estrutura taxonômica e trófico-funcional de comunidades de macroinvertebrados bentônicos de riachos de florestas tropicais de interior e litoral

Abstract

Tropical streams shaded by riparian forests are important components of the drainage network of a watershed, which in addition to being a source of water, has a biota that accounts for the processing of organic matter of allochthonous origin. Among the organisms that occur in this system, benthic macroinvertebrates deserve to be highlighted for their taxonomic diversity and variety of ecological functions. Benthic macroinvertebrates (aquatic insects, molluscs, crustaceans and worms) have dimensions larger than 0.2 mm and are found living between or on substrates (leaf litter, macrophytes, rocks, gravels and sand). These invertebrates participate in the degradation of organic matter, facilitating the role of decomposers and acting as a link between leaf debris and higher trophic levels (macroconsumers and aquatic and terrestrial predators), therefore essential for the flow of energy and nutrient dynamics. Different climatic and hydrological conditions can influence the types of riparian forests, consequently the characteristics of water and the structure of benthic macroinvertebrate communities. In addition, the greater presence of some taxonomic groups (such as decapods) may generate differences in the proportions of functional trophic groups (FTG). In this sense, the aim of the present study was to compare the taxonomic and trophic functional structure of the benthic macroinvertebrate community of tropical inland forest streams (Central region of Brazil) with coastal forest streams (Coastal region, São Paulo), in the rainy and dry seasons, in order to test the hypotheses that inland forest streams present greater variation in taxonomic structure (composition , abundance, richness and diversity) of benthic macroinvertebrate communities between the dry and rainy seasons, in relation to the coast and that inland forest streams and coast have different proportions of FTG, due to the presence of decapods. For this, two seasonal collections were carried out in the dry and rainy seasons in three inland streams and three coastal streams. In each stream, physical and chemical parameters of water, structural characteristics of the streams, canopy cover and substrate type were measured. Samples from macroinvertebrate communities obtained, and individuals identified up to the lowest possible taxonomic level (family) and classified into functional trophic groups. Seasonality influence recorded on OD concentration, pH, turbidity, water speed, canopy %, substrate % and on the structure of macroinvertebrate communities. There was no difference in taxonomic richness between seasons, however, abundance varied between rain and drought in both locals. The inland area had greater variation in the mean abundance of benthic macroinvertebrates than coastal ones. The diversity varied between seasons in both areas, presenting higher rates in the rainy season. Among the most contributory families for dissimilarity between seasons and between areas are Chironomidae, Leptophlebiidae, Sericostomatidae, Hydropsychidae, Atyidae and Palaemonidae (the latter two being found only on the coast). The catador-collector FTG was the most abundant in both study areas. Nevertheless, the classification of FTG showed differences between the areas (inland and coast), 81.45% and 55.75% of collectors, 2.83% and 8.99% of fragmenters, 5.93% and 2.02% of predators and 0.60% and 2.21% of scrapers, respectively. Thus, spatial factors seem to directly influence the proportion of FTG, corroborating the second hypothesis of this study. On the other hand, both spatial and temporal factors can significantly influence the abundance and diversity of macroinvertebrates, but little in richness. The dominanic of macroinvertebrates belonging to the group of collector scavers indicates the presence of fine debris and the importance of this food resource in tropical streams. In addition, the fragmenters were most abundant, suggesting that the presence of this group may not be as rare in streams of tropical forests. However, the classification of FTG particularly shrimps may be inconclusive, as the contribution to leaf debris fragmentation may vary among species of the family Atyidae. In general, the high representativeness of these macroconsumers in the system may have influenced the proportion of FTG.