Múltiplos estressores antrópicos em ecossistemas aquáticos: impactos no tamanho e biomassa da comunidade zooplanctônica.

Abstract

Freshwater ecosystems are fundamental for biodiversity and the provision of ecosystem services. However, they are highly vulnerable to environmental changes and anthropogenic pressures. In this context, the analysis of zooplankton size spectra and biomass is particularly relevant, as these organisms respond quickly to variations in environmental conditions. An experimental mesocosm study was conducted to evaluate the isolated and combined effects of increased temperature, nutrient enrichment, and reduced detritus input in aquatic environments on the size structure and biomass of the zooplankton community over a period of 160 days. The initial expectation was that warming, acting in isolation, would lead to a decrease in the size and biomass of organisms in the zooplankton community. In contrast, the presence of nutrients and detritus, individually, was expected to increase the mean size and biomass of the community; however, under warming conditions, the effects of nutrients and detritus were expected to be minimized. The experiment was conducted with treatments randomly distributed within blocks, comprising 60 experimental units (12 treatments × 5 replicates each). These included three thermal regimes (i - control warming, based on ambient temperature; ii - fluctuating warming, with temperature increases ranging from +2°C to +6°C relative to the control; iii - constant warming, with a continuous increase of +4°C relative to the control), two nutrient levels (i - with nutrient addition; ii - without nutrient addition), and two detritus levels (i - natural concentration; ii - an 80% reduction in detritus concentration). During the experiment, 61 species of the zooplankton community were recorded, with a predominance of rotifers and testate amoebae. Following the start of the experiment, the mean community size decreased until day 120, with recovery observed by day 160. For biomass, this attribute peaked on day 40, declining in the intermediate periods, mainly for testate amoebae and rotifers. Nutrient presence acted as a positive modulator of these attributes and constant warming was negatively associated with size and biomass values. In contrast, treatments with fluctuating warming often maintained or even exceeded the size and biomass values observed in both warming and control treatments. The distribution of biomass across size classes reinforced this pattern, with larger organisms predominating at the beginning, being replaced by smaller ones during intermediate stages, and showing partial recovery of larger organisms by the end of the experiment. These results demonstrate that multiple stressors interact in complex ways to shape zooplankton community structure, highlighting the importance of considering combined effects under global warming scenarios. Therefore, it is essential to evaluate how different environmental changes affect planktonic organisms.