Elizabeth Duskey | Search USGS

USGS2025

Using complementary biomarkers to unravel fish lifetime exposure to hypoxia and mercury

Aquatic ecosystems are losing oxygen due to climate change. This deoxygenation can favor microbial methylation of mercury (Hg). To understand the dynamics of Hg under increasing deoxygenation, we simultaneously quantified both Hg and hypoxia (< 2 mg O2/L) lifetime chronologies in fishes. We used a novel combination of chemical biomarkers in ear stones and eye lenses. We compared these markers in two species with different life histories, benthic Round Goby (Neogobius melanostomus) and semi-demersal Yellow Perch (Perca flavescens), from two connected ecosystems with different levels of hypoxia: the Central Basin of Lake Erie and the less hypoxic but more polluted Western Basin. Overall, Central Basin Round Goby were exposed to hypoxia throughout their lifetime and exhibited significantly elevated eye lens Hg concentrations ([Hg]) compared to their Western Basin counterparts. In contrast, the Central Basin Yellow Perch were exposed to hypoxia only at their juvenile stage. Central Basin Yellow Perch exhibited significantly lower eye lens [Hg] compared to their Western Basin counterparts. Patterns revealed by eye lens [Hg] were not detectable in muscle tissue [Hg]. Findings show that exposure to hypoxia can alter fish lifetime Hg accumulation patterns, with species-specific outcomes.

central and western basins of Lake Erie↗

USGS2020

Seasonal habitat use indicates that depth may mediate the potential for invasive round goby impacts in inland lakes

The round goby ( Neogobius melanostomus ) is among the fastest-spreading introduced aquatic species in North America and is radiating inland from the Great Lakes into freshwater ecosystems across the landscape. Predicting and managing the impacts of round gobies requires information on the factors influencing their distribution in habitats along the invasion front, yet this information is not available for many recently invaded ecosystems. We evaluated the seasonal habitat use and biomass of round gobies in an inland temperate lake to define the spatiotemporal scope of biological interactions at the leading edge of the round goby invasion. Using novel statistical approaches, we combined hierarchical models that control for imperfect species detection with flexible smooth terms to describe non-linear relationships between round goby abundance and environmental gradients. Subsequently, we generated accurate detection-corrected estimates of the standing stock biomass of round gobies. Our results show seasonally differentiated habitat niches, where suitable round goby habitat in summer months is restricted to shallow depths (<18.4 m) with a mixture of vegetative and mussel cover. We found high round goby biomass of 122 kg/ha in occupied habitats during the summer, with a total lake-wide biomass of 766,000 kg. In winter, round gobies migrate to deep offshore habitats and disperse, dramatically altering their scope for biological interactions with resident aquatic species across summer and winter seasons. The results of this study indicate that the scope of biological interactions in inland lakes may be seasonally variable, with potential for high round goby biomass in shallow lakes or at the periphery of deep lakes in the summer months. Such shallow-water habitats may therefore present higher risk of ecological impacts from round gobies in invaded lentic ecosystems. As round gobies expand inland, consideration of seasonal habitat use will be an important factor in predicting the impacts of this pervasive invader.

New York↗