Who’s cooking, who’s cleaning, and who’s got the remote control within the waters blanketing Earth? Anatomically tiny, numerically dominant microbes are the crucial “homemakers” of the watery household. Phytoplankton’s culinary abilities enable them to create food by absorbing sunlight to fix carbon and release oxygen, making microbial autotrophs top-chefs in the aquatic kitchen. However, they are not the only bioengineers that balance this complex household. Ubiquitous heterotrophic microbes including prokaryotic bacteria and archaea (both “bacteria” henceforth), eukaryotic protists, and viruses, recycle organic matter and make inorganic nutrients available to primary producers. Grazing protists compete with viruses for bacterial biomass, whereas mixotrophic protists produce new organic matter as well as consume microbial biomass. When viruses press remote-control buttons, by modifying host genomes or lysing them, the outcome can reverberate throughout the microbial community and beyond. Despite recognition of the vital role of microbes in biosphere housekeeping, impacts of anthropogenic stressors and climate change on their biodiversity, evolution, and ecological function remain poorly understood. How trillions of the smallest organisms in Earth’s largest ecosystem respond will be hugely consequential. By making the study of ecology personal, the “housekeeping” perspective can provide better insights into changing ecosystem structure and function at all scales.

Around the world, freshwater lakes are increasingly suffering from harmful algal blooms (HABs) as a result of anthropogenic eutrophication. Muskegon Lake (Muskegon, Michigan, USA), a drowned river mouth, Great Lakes estuary, was declared an Area of Concern by the Environmental Protection Agency in 1987 with nuisance algal blooms cited as a beneficial-use impairment. The objective of this study was to quantify changes in HAB prevalence and assemblage composition in Muskegon Lake over 14 y (2003-2016) and explore the environmental factors potentially driving the changes. We performed univariate and multivariate analyses on long-term monitoring data, including environmental and phytoplankton data, to understand their relationships and temporal variation. Using linear regressions, we assessed changes in environmental variables over time and relationships between cyanobacteria biovolume and environmental variables. We used non-metric multidimensional scaling to visualize variation in annual cyanobacteria assemblage composition and association with environmental variables. Analyses revealed that, despite generally rising water temperatures, which would be expected to increase HABs, a reduction in nutrient concentrations caused by restoration efforts has likely led to substantial decreases in HAB abundance over time. Additionally, HAB assemblage composition appears to be driven by temperature and nutrient form and amount, with Microcystis (Lemmermann, 1907) often dominating. HABs in freshwater bodies should be closely monitored into the future as we enter an era of uncertain climatic conditions.

Beavers are keystone species that modify ecosystem structure and function through dam building, thereby creating a complex mosaic of lotic and lentic ecosystems. We assessed the influence of Eurasian beavers ( Castor fiber ) on cellulose decomposition using a cotton-strip assay and compared physical and chemical conditions between upstream reference reaches and beaver ponds in five low-order streams in Hungary. Standardized cotton strips were deployed in both aquatic and shoreline habitats at each site. Cotton-strip decomposition, measured as tensile-strength loss, was significantly faster in upstream reference reaches than in beaver ponds and faster in aquatic habitats than in shoreline habitats. Turbidity, pH, dissolved oxygen, and oxygen saturation were higher in reference reaches than in beaver ponds, whereas most measured chemical variables did not differ significantly. Additional multivariate analysis indicated that decomposition was associated with several physical and chemical gradients rather than with any single environmental variable. Overall, our results suggest that beaver dams modify habitat conditions and reduce cellulose decomposition rates in ponded reaches. These changes may influence organic matter processing and carbon retention pathways, although direct measurements of carbon pools and greenhouse-gas fluxes are needed to evaluate whether beaver-modified habitats function as net carbon sinks.