Comparing nearshore benthic and pelagic prey as mercury sources to lake fish: the importance of prey quality and mercury content

Abstract

Mercury (Hg) bioaccumulation in fish poses well-known health risks to wildlife and humans through fish consumption. Yet fish Hg concentrations are highly variable, and key factors driving this variability remain unclear. One little studied source of variation is the influence of habitat-specific feeding on Hg accumulation in lake fish. However, this is likely important because most lake fish feed in multiple habitats during their lives, and the Hg and caloric content of prey from different habitats can differ. This study used a three-pronged approach to investigate the extent to which habitat-specific prey determine differences in Hg bioaccumulation in fish. This study first compared Hg concentrations in common nearshore benthic invertebrates and pelagic zooplankton across five lakes and over the summer season in one lake, and found that pelagic zooplankton generally had higher Hg concentrations than most benthic taxa across lakes, and over a season in one lake. Second, using a bioenergetics model, the effects of prey caloric content from habitat-specific diets on fish growth and Hg accumulation were calculated. This model predicted that the consumption of benthic prey results in lower fish Hg concentrations due to higher prey caloric content and growth dilution (high weight gain relative to Hg from food), in addition to lower prey Hg levels. Third, using data from the literature, links between fish Hg content and the degree of benthivory, were examined, and showed that benthivory was associated with reduced Hg concentrations in lake fish. Taken together, these findings support the hypothesis that higher Hg content and lower caloric content make pelagic zooplankton prey greater sources of Hg for fish than nearshore benthic prey in lakes. Hence, habitat-specific foraging is likely to be a strong driver of variation in Hg levels within and between fish species.

Ecomorphological divergence drives differential mercury bioaccumulation in polymorphic European whitefish (Coregonus lavaretus) populations of subarctic lakes

“…Both grow quickly until maturation, suggesting high pelagic zooplankton consumption and high metabolic energy demand. The putatively lower per unit energy content of zooplankton compared to benthic macroinvertebrates, and subsequently increased consumption, may further enhance their exposure compared to benthic morphs (Karimi et al, 2016). Zooplankton foraging also requires more active swimming to capture evasive prey compared to foraging on more sedentary benthic prey, increasing the metabolic cost for pelagic morph (Trudel et al, 2001).…”

“…in the transport of methylmercury to fish in high-latitude lakes (Chételat and Amyot, 2009;Kahilainen et al, 2016a). Despite the low mercury content of individual Daphnia, planktivorous fish may consume thousands of individuals per day, potentially explaining their prominent role in mercury transfer pathways (Karimi et al, 2016). In contrast, benthic macroinvertebrates have a broad range of foraging guilds, resulting in differential uptake, complicating mercury transfer processes to fish.…”

Mercury bioaccumulation increases with latitude in a coastal marine fish (Atlantic silverside,Menidia menidia)

“…1978, Karimi et al 2016) also affect MeHg bioaccumulation. Assimilation of inorganic forms of dietary Hg, on the other hand, is thought to be negligible (<15%) given the much faster turnover rate of assimilated inorganic Hg compared to MeHg (Dutton and Fisher 2010).…”

“…Overall, MeHg bioaccumulation is the net result of interacting physiological processes and environmental factors. In particular the feedbacks between dietary intake, growth, and MeHg bioaccumulation are still insufficiently understood (Braune 1987, Doyon et al 1998, Karimi et al 2016). Such knowledge would arguably improve the interpretation of MeHg patterns in wild fish populations, particularly when patterns are compared across large geographic regions.…”

Evaluation of mercury cycling and hypolimnetic oxygenation in mercury-impacted seasonally stratified reservoirs in the Guadalupe River watershed, California

“…MeHg in lake water can bioaccumulate to concentrations in predator fish over one million‐fold higher than their ambient waters [ Davis et al ., ]. Plankton dynamics and trophic bioaccumulation pathways can also influence MeHg concentrations in top trophic‐level fish [ Stewart et al ., ; Karimi et al ., ]. Many studies have attempted to find correlations between fish MeHg concentrations and physical and chemical lake characteristics, and parameters such as lake morphology [ Mason and Sveinsdóttir , ] and mercury levels in zooplankton [ Chen et al ., ] have been found to be of primary importance.…”