A eco-exergia de macroinvertebrados e fitoplâncton em resposta ao gradiente espacial de precipitação no semiárido

Abstract

Precipitation is an environmental variable recognized as a driver of the structuring of aquatic ecosystems. This variable has an even more striking role in ecosystems located in arid areas, where it can present a spatial distribution that generates the formation of environmental gradients. Environmental gradients have effects on freshwater biota, so it is important to understand the role of these gradients on energy storage in these ecosystems. The indexes of eco-exergy and specific eco-exergy act as a tool capable of capturing changes in energy storage and information stored in the genome of organisms, being widely applied in ecological studies. In this perspective, this work aimed to evaluate the response of eco-exergy and specific eco-exergy of phytoplankton and benthic macroinvertebrate communities to changes in environmental conditions within a spatial gradient of precipitation in the semiarid. For this, we tested the hypotheses (i) with the reduction of precipitation, the reservoirs will present a higher concentration of nutrients, which favors the dominance of taxa of generalist macroinvertebrates and organisms of the group of cyanophytes in the phytoplankton community; (ii) with the decrease in precipitation, communities will present a higher concentration of eco-exergy, due to the greater storage of phytoplankton biomass and generalist macroinvertebrates, as well as a low specific eco-exergy, resulting from the low investment in information reflected in a reduced wealth and diversity. To test these hypotheses, we evaluated 13 artificial reservoirs located within a spatial gradient of precipitation in the semiarid. In each reservoir we sampled organisms from the community of benthic macroinvertebrates and phytoplankton, as well as the physical and chemical variables of the water. In each community we measure the specific eco-exergy and eco-exergy, Shannon's wealth and diversity index. We performed Spearmann Correlation tests between environmental variables and biological indices in relation to the spatial gradient of precipitation. In our results, the environmental variables that were influenced by the gradient are depth, total organic carbon (TOC), chlorophyll and transparency. The richness, diversity, eco-exergy index and specific eco-exergy of the phytoplankton community did not respond to the precipitation gradient. However, for the benthic macroinvertebrate community, all indexes tested showed a pattern of reduction with increasing precipitation. We found that the spatial variation of precipitation acted as an energetic and taxonomic driver only for the benthic macroinvertebrate community.