Fontes basais de carbono e cadeia alimentar planctônica em um lago tropical produtivo

Abstract

All organisms are part of a complex network of feeding relationships composed by multiple links. Particularly in lakes, where producers and consumers do not always share the same habitat, trophic connections between habitats are ubiquitous and may be central to food web dynamics. The zooplankton of lakes plays an important link between basal carbon sources and organisms in higher trophic positions. Therefore, the aim of this study was to determine the basal carbon sources and the trophic relationships between zooplankton size fractions in a tropical productive lake (Lake Carioca, MG, Brazil) through the natural distribution of carbon and nitrogen stable isotopes. Sampling of sources (seston, periphyton, aquatic macrophytes and litter) and consumers (micro and mesozooplankton and Chaoboridae larvae) was done during the wet season of 2012 and the dry season of 2013. Data were analyzed through Bayesian mixing models for stable isotopes with SIAR package in R. The main basal carbon source supporting Lake Cariocas pelagic food web varied between seasons, with the terrestrial source (litter) being the most important during the wet season (56.7%) and the pelagic source (seston) being the most important during the dry season (56.3%). Planktonic food web structure also varied between seasons: during the wet season all zooplankton size fractions occupied different trophic positions, while during the dry season mesozooplankton and Chaoboridae larvae shared the same trophic position. Thereby, this study demonstrated that although Lake Carioca is a productive lake, its zooplankton and all food chain that depends on it - depends not only on aquatic but also on terrestrial carbon sources, and that the contribution of these sources as well as the planktonic food web structure varied between seasons. These findings have important implications to the conservation of this ecosystem and all Rio Doce valley lakes in general.