Increased anoxia following species invasion of a eutrophic lake

Abstract

Species invasions can disrupt aquatic ecosystems by re‐wiring food webs. A trophic cascade triggered by the invasion of the predatory zooplankter spiny water flea (Bythotrephes cederströmii) resulted in increased phytoplankton due to decreased zooplankton grazing. Here, we show that increased phytoplankton biomass led to an increase in lake anoxia. The temporal and spatial extent of anoxia experienced a step change increase coincident with the invasion, and anoxic factor increased by 11 d. Post‐invasion, anoxia established more quickly following spring stratification, driven by an increase in phytoplankton biomass. A shift in spring phytoplankton phenology encompassed both abundance and community composition. Diatoms (Bacillaryophyta) drove the increase in spring phytoplankton biomass, but not all phytoplankton community members increased, shifting the community composition. We infer that increased phytoplankton biomass increased labile organic matter and drove hypolimnetic oxygen consumption. These results demonstrate how a species invasion can shift lake phenology and biogeochemistry.

Bacterial ecology and evolution converge on seasonal and decadal scales

“…Another possible driver is the irruption of the invasive zooplankton spiny water flea ( Bythorephes cedertrömii ) in 2009. This major disturbance resulted in a trophic cascade that decreased water clarity 19,31 , increased lake anoxia 28 , and shifted the bacterial community composition 13 . Although the abrupt changes in strain composition of seven Nanopelagicaceae species were observed three years later, lag effects are common in complex ecosystems 32 .…”

“…4e). These climatic conditions led to top-down and bottom-up controls on the lake's primary productivity: the highest spring zooplankton abundance since measurements began in 1994 28 (Fig. 4d) was likely a result of the mild winter and spring allowing zooplankton populations, especially the prolific grazer Daphnia pulicaria to establish early, and low total phosphorus and soluble reactive phosphorus (Fig.…”

“…To place environmental conditions in 2012 in context, historical environmental data was collected from the North Temperate Lakes Long-Term Ecological Research program (NTL-LTER) through the Environmental Data Initiative (EDI) interface (https://edirepository.org/) and the US Geological Survey (USGS) Water Data for the Nation (https://waterdata.usgs.gov/nwis) using the USGS dataRetrieval R package (version 2.7.14) 68 . EDI datasets analyzed included ice duration 26 ; nutrients, pH, and carbon 41 ; major ions 42 ; water temperatures combined from multiple datasets [45][46][47][48][49] as described in Rohwer et al 13 ; phytoplankton 43 ; and zooplankton 44 converted to biomass as described in Rohwer, Ladwig, et al 28 . River discharge measurements were obtained from the USGS for the Yahara River, the primary tributary into Lake Mendota (site ID: 05427718) 27 .…”