Controles da produção primária em um Córrego de Mata Atlântica

Abstract

This dissertation consists of two chapters, each corresponding to an independent study. In an Atlantic Rainforest stream, Rio de Janeiro, Brazil, the effects of herbivores and of environmental controls on periphyton were studied. In the first experiment I tested the effects of the shrimp Potimirim glabra, an ecosystem engineer, on the metabolic parameters of periphytic communities (Production, Respiration, Net Daily Metabolism and Production:Respiration ratio). The Potimirim inclusion treatments produced results opposite to the expected, with higher chlorophyll and dry mass of the periphytic communities. This lead to doubt of the efficacy of the treatments. None of the metabolic variables was related to the treatments. It is considered that artificial effects of the cage used in the shrimp inclusion may have changed the expected effect of material removal by the shrimps. The results may hint, however, that the chlorophyll and dry mass parameters may be more sensitive to and variable with the effects of herbivores than the metabolic parameters in the studied communities. Future work is recommended with methods that reduce artificial effects, such as herbivore exclusion using electric fences. In the second experiment, stocks, distribution and controls of periphytic biomass were studied for the stream. Among the studied substrates, sand presented the highest stocks, with 5 times more chlorophyll and 20 times more dry mass than the rock and leaf substrates. Differences among reaches with different densities of the herbivore shrimp Potimirim glabra revealed for the stone substrate smaller dry mass values in the reaches where the shrimp is more abundant. Among environmental variables, only depth was related to biomass, in the substrates rock and sand. The comparison of data in this study with previous work may hint that disturbances caused by spates may change stocks and distribution patterns for this stream.