Lake Bacterial Assemblage Composition Is Sensitive to Biological Disturbance Caused by an Invasive Filter Feeder

Abstract

Freshwater bacteria play fundamental roles in global elemental cycling and are an intrinsic part of local food webs. Human activities are altering freshwater environments, and much has been learned regarding the sensitivity of bacterial assemblages to a variety of these disturbances. Yet, relatively few studies have focused on how species invasion, which is one of the most important aspects of anthropogenic global change, affects freshwater bacterial assemblages. This study focuses on the impact of invasive dreissenid mussels (IDMs), a globally distributed group of invasive species with large impacts on freshwater phyto- and zooplankton assemblages. We show that IDMs have direct effects on lake bacterioplankton abundance, taxonomic composition, and inferred bacterial functional group representation.

Flow cytometric monitoring of bacterioplankton phenotypic diversity predicts high population‐specific feeding rates by invasive dreissenid mussels

“…The experiment consisted of 12 l microcosms of 153 µm screened water and quagga mussels, both retrieved from Lake Michigan. The Lake Michigan bacterioplankton has previously been shown to contain both grazing‐resistant and grazing‐sensitive taxa allowing the study of direct grazing impacts (Tang et al ., ; Denef et al ., ). Prior to the onset of the experiment, we assessed whether the previously established correlation between phenotypic and taxonomic diversity metrics for low diversity environments could be extended to higher diversity aquatic environments, such as Lake Michigan.…”

“…To put these measurements in perspective, we analysed data from a recently published mussel‐feeding study that used the same experimental design and had 16S rRNA gene amplicon data at time points 0 and 3 h available (Fig. ) (Denef et al ., ). We calculated a mean loss of taxonomic diversity (D 2 ) of 5.32 ± 4.65 for their three independent experiments, which is comparable to the taxonomic diversity loss predicted for our experiment (2.6 ± 1.0).…”

“… Measured or predicted taxonomic alpha diversity of Lake Michigan bacterioplankton communities after a three hour exposure to invasive quagga mussels. Measured taxonomic diversity data is publicly available from Denef and colleagues (). The measured data comes from feeding experiments that were carried out with Lake Michigan bacterioplankton communities retrieved over a two year period and under the identical experimental design as described in this manuscript.…”

“…For river bacterioplankton, short‐term mesocosm experiments provided no evidence of a direct feeding effect, while long‐term environmental surveys suggested a doubling in bacterioplankton densities (Findlay et al ., ). In lakes, feeding on bacteria in low nutrient systems was thought to be limited (Cotner et al ., ), though short‐term feeding experiments on natural bacterioplankton from Lake Michigan did detect significant decreases in bacterioplankton densities (Denef et al ., ).…”

“…With respect to their feeding behaviour, IDMs show highly selective feeding behaviour toward seston and different algal and microzooplankton taxa over a broad range of size (∼ 1–200 µm) (Tang et al ., ). While IDMs are known to strongly impact phytoplankton and zooplankton abundance and composition (Higgins and Vander Zanden, ), the few studies focused on their impacts on bacterioplankton report contradicting results Several of these studies reported selective feeding on bacterial species (Silverman et al ., ; Pires et al ., ; Denef et al ., ), while a long‐term environmental survey of the Hudson River prior‐ and post‐invasion did not observe negative effects on bacterial community density and productivity (Findlay et al ., ).…”