Freshwater Macroinvertebrates Drive Planktonic Bacterial Community Composition and Activity in Microcosms

ABSTRACT Nutrient cycling and organic matter transformations in aquatic systems are primarily performed by microorganisms but are further facilitated through the mixing of sediment by macroinvertebrates. Despite known impacts of macroinvertebrates on the biogeochemistry and microbial community of sediments, the impact of macroinvertebrates and their microbiome on the water column of freshwater systems has been understudied. A microcosm approach was used to study the short‐term effects that freshwater bivalves, Corbicula fluminea , and crayfish, Procambarus vioscai paynei , have on the microbial community in the surrounding water column. The activity of microbial enzymes involved in the breakdown of organic carbon (β‐glucosidase), phosphate (phosphatase), and carbon and nitrogen ( N ‐acetylglucosaminidase) were assayed, and the bacterial community in the water column and other system components was characterised using Illumina 16S rRNA gene sequencing. Crayfish and bivalves both significantly altered the structure and function of the bacterial community in the water column. Crayfish stimulated microbial enzyme activity to a greater extent than bivalves, whereas bivalves at higher densities increased water column enzyme activity more than when they were at lower densities. The external microbiomes of macroinvertebrates were not a significant source of bacterial populations to the bacterial communities of vegetation or the water column, but macroinvertebrate presence was associated with an increased abundance of certain bacterial taxa in the water column, such as Comamonadaceae and Chitinophagaceae. These results demonstrate that, even in the short term, macroinvertebrates can impact biogeochemical processes in the water column of freshwater ecosystems, potentially by influencing the bacterial community. This study contributes to a deeper understanding of the relationships between macroinvertebrates and microbial communities in their environment, with specific implications for processes in the water column, a component that is frequently overlooked in terms of macroinvertebrate effects. Considering interactions between all components of freshwater ecosystems is crucial to understanding their functioning, especially in the face of escalating environmental pressures.