Pelagic phytoplankton community change‐points across nutrient gradients and in response to invasive mussels

Abstract

Summary Phytoplankton communities can experience nonlinear responses to changing nutrient concentrations, but the nature of species shifts within phytoplankton is not well understood and few studies have explored responses of pelagic assemblages in large lakes. Using pelagic phytoplankton data from the Great Lakes, we assessed phytoplankton assemblage change‐point responses to nutrients and invasive Dreissena, characterising community responses in a multi‐stressor environment and determine whether species responses to in situ nutrients can be approximated from nutrient loading. We demonstrate assemblage shifts in phytoplankton communities along major stressor gradients, particularly prominent in spring assemblages, providing insight into community thresholds at the lower end of the phosphorus gradient and species‐stressor responses in a multi‐stressor environment. We show that responses to water nutrient concentrations could not be estimated from large‐scale nutrient loading data likely due to lake‐specific retention time and long‐term accumulation of nutrients. These findings highlight the potential for significant accumulation of nitrates in ultra‐oligotrophic systems, nonlinear responses of phytoplankton at nutrient concentrations relevant to current water quality standards and system‐specific (e.g. lake or ecozone) differences in phytoplankton responses likely due to differences in nutrient co‐limitation and effects of dreissenids.

The effects of nutrient enrichment and invasive mollusks on freshwater environments

“…Nutrient pollution should also increase the success of filter‐feeding invasive species due to an increased density of food resources (e.g., phytoplankton). Nutrient additions could allow for sustained high‐density populations of invasive filter feeders, despite the typical shift in the energy pathway from pelagic to benthic, that might limit the population size of invasive bivalves (Higgins and Zanden 2010, Gallardo et al 2016, Kovalenko et al 2017). Additionally, invasive filter feeders have very high filtration rates (Fanslow et al 1995), allowing for the exploitation of phytoplankton resources, which can have cascading ecological effects in freshwater environments (Stewart and Haynes 1994, Strayer et al 1999).…”

Carbon and nitrogen recycling during cyanoHABs in dreissenid-invaded and non-invaded US midwestern lakes and reservoirs

“…As filter feeders, invasive non-native mussel species may improve water clarity and increase the depth of light penetration and have been linked to an increase in the productivity of toxin-producing cyanobacteria (Hecky et al, 2004), and an increase in M. aeruginosa biomass (Vanderploeg et al, 2002;Sarnelle et al, 2005). Mussels can also recycle nutrients contained in microbial biomass back into the water column (Kovalenko et al, 2017). All of these characteristics may assist the establishment and proliferation bloomforming cyanobacteria.…”