O efeito dos invertebrados aquáticos na decomposição de detritos foliares: uma meta-análise

Abstract

There is no study aimed to synthesize the magnitude and variation of aquatic invertebrates for the decomposition of leaf litter in aquatic ecosystems. Furthermore, there is also a lack of knowledge about what is the overall impact of these small organisms on leaf decomposition. Moreover, there are a number of controversies that are the most influential factors on one of the most important processes of aquatic ecology. For example, the influence of latitude and temperature or yet the methodology employed for measuring the effect of the aquatic detritivorous invertebrates. Therefore the aim of our study was, through a meta-analytic review, understand how these organisms affect the decomposition of foliar detritus in aquatic ecosystems, and how this effect varies according to the methodological and environmental parameters most used. Through the evaluation of decomposition rates (k) in the presence and absence of these invertebrates 104 independent studies satisfied our selection criteria and were included in the database. To intention present representativeness of the sample, each used parameter in this analysis need to be present in over 90% of the selected studies. No publication bias was detected, although we verified a significant decrease in the invertebrate decomposition effect in longer experimental duration, indicating that short experiments reveal higher detritivoria while longer experiments manifest lower mass loss. As expected, these results cast reveal that in general the presence of invertebrates accelerates the decomposition process. Furthermore the global effect size, these effect are consistent and do not differ in relation to aquatic ecosystem types (lotic, lentic or marine), temperature or latitude of the experiments, even presenting a slight increase importance of invertebrates in the decomposition process toward lower latitudes. Therefore, this analysis contradicts the argument that invertebrates have a greater role in the decomposition of aquatic ecosystems at higher latitudes while microorganisms would be more important at minors. Temperature result also contradicts the preview and results of this and other reviews where it could reveal some variation of invertebrate effect. No weakness of invertebrate exclusion methods (mesh bags, electric field or toxic) or even the standardized mesh bag difference (a standardized difference between coarse and fine mesh bags) was found. In contrast to the most of literature, these parameters did not show any significant relationship with the effect size. However should be difficult affirm there is no additive effects of experimental exclusion or also standardized mesh size difference. Conversely, other factors interfere significantly in the decomposition mediated by invertebrates such as detritus origin (allochthonous or autochthonous) and experimental duration. Probably other parameters besides the not included in this analysis could explain the effect of invertebrates on leaf decomposition, however an insufficient number of available parameters hamper this assay. We conclude that this synthesis indicates that the role of detritivorous invertebrates should be included in biogeochemical models, which consider nutrient cycling in temperate or tropical aquatic ecosystems. More specifically these models should incorporate environmental parameters such as detritus origin, as well methodological parameters such as experimental duration.