Produção secundária e esforço amostral de macroinvertebrados em um córrego de Mata Atlântica

Abstract

Macroinvertebrate secondary production studies in streams present a diversity of ecological issues such as energy flow in ecosystems and analysis of trophic relationships, which are fundamental for understanding the trophic structure. The objective of this research was to measure the secondary production in five sampling sites distributed over an Atlantic Forest stream at Ilha Grande (RJ) on a shading gradient of 12-92% of canopy opening. We evaluate the sampling effort required the collection of macroinvertebrates and some factors that influence the secondary production. Four richness estimators (Chao, Jack 1, Jack 2, Boot) were used to identify the sampling effort for collections of macroinvertebrates. The curves showed a similar pattern and absence of erratic behavior. Jack 2 was the best performer among the evaluated criteria. Species richness observed in 279 samples surbers can be estimated using 83 samples surbers. We expect that the secondary production of shredders decreases with decreasing shading and that the production of scrapers and gatherers are the inverse. We also hope that the presence of fish influences directly the production of Baetidae, Potimirim brasiliana and Chironomidae. The secondary production rates of the macroinvertebrate community ranged along the river according to shading, with changes in the substrate-habitat and predation. Overall, there was an increase in production rate in the less shaded points (832 - 7486 mg dry mass.m-².ano-¹). Shredders had higher production in sites more shaded, and the production of scrapers and collectors increased downstream. Collectors had the highest production at all points except at the more shaded site. More than 90% of secondary production at every point was supported by three species. The theory of River Continuous provides longitudinal changes in the availability of resources and consequently the fauna distribution. The theory was useful to formulate our assumptions regarding factors that may affect secondary production along the river. Production in our study was low and the P/B high compared to study in temperate environment. This may be related to patterns of short life cycles and high growth rates influenced by high temperatures in tropical environments. The presence and absence of fish at the sites studied showed a trophic cascade effect. The presence of fish was significant for Chironomidae production, which was higher in spots with fish. The production of benthic predators and Baetidae did not differ between sites with and without fish and the production of P. brasiliana was null in sites with fish. We suggest that the presence of fish inhibit the presence of this shrimp and that in the absence of grazing, the periphyton becomes thicker serving as shelter and food for the Chironomidae. The direct effect of fish in Baetidae seems bigger than in P. brasiliana.