Efeitos da arquitetura das macrófitas e dos macroinvertebrados sobre a estrutura de algas epifíticas em um reservatório tropical

Abstract

This thesis aims to understand the factors that influence the structure of periphytic algae and macroinvertebrate communities in a tropical reservoir, considering the functional characteristics and beta diversity of periphytic algae species, in addition to understanding the top-down effects exerted by fish on periphytic algae and macroinvertebrates in continental aquatic ecosystems. The study was carried out at five different points in the Jazigo reservoir, Serra Talhada, PE, Brazil. A quarterly monitoring was carried out, between the years 2017 to 2018 (n = 4), to understand the role of limnological and biotic variables (structural complexity of macrophytes) on the structure and functional characteristics of periphytic algae communities and macroinvertebrate structure. The effects of environmental filters on the beta diversity of periphytic algae, and an in situ experiment to evaluate fish on the biomass of periphytic algae, macroinvertebrates and macrophytes. The structural attributes (wealth, biomass, abundance and diversity) of periphytic algae and macroinvertebrates were driven by the morphological complexity of macrophytes. RLQ analysis showed that loosely adhered and entangled species were positively correlated with light intensity and dissolved oxygen; prostrate species correlated positively with macrophytes of medium structural complexity. Colonial species correlated positively with nitrate, ammonia, dissolved inorganic nitrogen and macrophytes with low complexity; while unicellular species, heterotricomas and filamentous ones correlated positively with conductivity, temperature and macrophytes with high structural complexity. These effects were also observed on the beta diversity of periphytic algae. Alpha and beta diversity were higher in macrophytes with greater morphological complexity. Furthermore, the presence of different species of macrophytes contributed to the increase in richness and beta diversity of periphytic algae. Substitution was the determining component of the beta diversity of periphytic algae and was greater in macrophytes of greater morphological complexity, Eichhornia crassipes and Ludwigia helminthorrhiza. This component has a strong relationship with complex habitats. Furthermore, the beta diversity of periphytic algae was driven mainly by physical (51.34%) and chemical (31.14%) variables, and by macroinvertebrates (4.21%). Redundancy analysis explained 65% of the distribution of periphytic algae with environmental filters (physical, chemical and biological) Dissolved inorganic nitrogen, macrophyte morphological complexity, temperature, macroinvertebrate abundance, light intensity and dissolved oxygen were important to explain beta diversity of periphytic algae. Therefore, physical and chemical factors act as environmental filters on periphytic algae. The top-down effect exerted by fish on macroinvertebrates showed the efficiency of the manipulation of omnivorous fish in controlling the biomass of macroinvertebrates and indirectly the biomass of periphytic algae and macrophytes in a tropical reservoir. After 30 days, all treatments with the addition of omnivorous fish showed a reduction in macroinvertebrate biomass and an increase in periphytic algae biomass. In the treatment without the addition of fish and only in the presence of macroinvertebrates, the biomass of periphytic algae reduced and the biomass of macrophytes increased throughout the experiment. This thesis contributes to the understanding of the role of limnological and macrophyte variables with different morphological complexities on the structure of the periphytic algae and macroinvertebrate community. Environmental filters have shown to play a fundamental role on the beta diversity of periphytic algae and the importance of the presence of macrophytes for increasing habitat heterogeneity and consequent availability of niches and microhabitats for aquatic biodiversity. Finally, we observed that omnivorous fish can directly control the biomass of macroinvertebrates and indirectly the biomass of periphytic algae and macrophytes. Thus, new control strategies can be developed that can improve the efficiency of ecosystem functioning and conservation of aquatic biodiversity in tropical reservoirs.