Effects of Non‐native Fish on Lacustrine Food Web Structure and Mercury Biomagnification along a Dissolved Organic Carbon Gradient

Abstract

Although the introduction of non-native fish species has been shown to alter trophic ecology in aquatic ecosystems, there has been limited research on how invasive species alter methylmercury (MeHg) biomagnification in lacustrine food webs. We sampled surface water and biota from 8 lakes in Quebec, Canada, spanning a range of dissolved organic carbon (DOC) concentrations (2.9-8.4 mg/L); 4 lakes were inhabited by native brook trout (Salvelinus fontinalis), and the remaining lakes contained brook trout and a non-native fish, Allegheny pearl dace (Margariscus margarita). Periphyton, zooplankton, macroinvertebrates, and fish were analyzed for: 1) stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios to delineate food webs, and 2) total Hg (THg) or MeHg. Compared with the brook trout from reference lakes, fish from invaded lakes had higher length-standardized THg concentrations as well as a narrower dietary range and elevated trophic level, inferred from unadjusted δ 13 C and δ 15 N values, respectively. The rate of Hg biomagnification was similar across invaded and reference lakes, implying little effect of the invasive fish on the trophic transfer of MeHg. Despite differences in food web structure due to pearl dace invasion, DOC was the strongest predictor of brook trout THg levels for all lakes, suggesting that underlying environmental factors exerted a stronger influence on brook trout THg concentrations than the presence of a nonnative forage fish.

Spiny water flea invasion alters fish mercury bioaccumulation rates

“…The long list of studies to date that have examined sh Hg following species invasions and found little to no effect have often invoked the concept of growth altering sh Hg to explain their results (e.g., Johnston et al 2003;Hogan et al 2007; Barst et al 2020), but our study is one of the very few to explicitly evaluate the potential impact of invasive species on sh growth in modulating sh Hg concentrations. While 'growth dilution' is commonly invoked as an explanatory factor in reduced sh Hg in the literature, studies clearly demonstrating evidence for increased conversion e ciency leading to reduced Hg concentrations in sh are infrequent (Trudel and Rasmussen 2006), and actual empirical demonstrations of the process are similarly scarce (see Ward et al 2010 as a rare example).…”