Both mercury (Hg) and polychlorinated biphenyls (PCBs) demonstrate food web biomagnification in aquatic ecosystems, yet their toxicokinetics have not been simultaneously contrasted within a common ...fish species. This study quantifies uptake and elimination rates of Hg and PCBs in goldfish. Fish were exposed to contaminated food containing PCBs and Hg to determine dietary chemical assimilation efficiencies (AEs) and elimination coefficients (k tot). To test first-order kinetics, three exposure regimes were established by varying the proportion of contaminated fish incorporated into the food. Dietary AEs were 98 ± 10, 75 ± 12, and 40 ± 9% for MeHg, THg, and PCBs, respectively. The k tot values were 0.010 ± 0.003 and 0.010 ± 0.002 day–1 for THg and MeHg, respectively. No significant differences were found in k tot among the dosing levels for either THg or MeHg, confirming that Hg elimination is a first-order process. For PCB, k tot ranged from 0.007 to 0.022 day–1 and decreased with an increase in hydrophobicity. This study revealed that Hg had an AE higher than that of PCBs, while the k tot of Hg was similar to those measured for the most hydrophobic PCBs. We conclude that Hg has a bioaccumulation potential in goldfish 118% higher than the highest PCB BMF observed for congeners with a log K OW of >7.
Explosive speciation in ancient lakes has fascinated biologists for centuries and has inspired classical work on the tempo and modes of speciation. Considerable attention has been directed towards ...the extrinsic forces of speciation—the geological, geographical and ecological peculiarities of ancient lakes. Recently, there has been a resurgence of interest in the intrinsic nature of these radiations, the biological characteristics conducive to speciation. While new species are thought to arise mainly by the gradual enhancement of reproductive isolation among geographically isolated populations, ancient lakes provide little evidence for a predominant role of geography in speciation. Recent phylogenetic work provides strong evidence that multiple colonization waves were followed by parallel intralacustrine radiations that proceeded at relatively rapid rates despite long‐term gene flow through hybridization and introgression. Several studies suggest that hybridization itself might act as a key evolutionary mechanism by triggering major genomic reorganization/revolution and enabling the colonization of new ecological niches in ancient lakes. These studies propose that hybridization is not only of little impediment to diversification but could act as an important force in facilitating habitat transitions, promoting postcolonization adaptations and accelerating diversification. Emerging ecological genomic approaches are beginning to shed light on the long‐standing evolutionary dilemma of speciation in the face of gene flow. We propose an integrative programme for future studies on speciation in ancient lakes.
Eutrophication of freshwaters is already a problem in many regions globally and will probably worsen as human populations grow and consume more resources. The ability of researchers and governments ...to anticipate, mitigate, and restore eutrophic freshwaters in a cohesive, integrated manner suffers from key uncertainties in our understanding of the watershed-to-lake continuum. Here, we use Lake Erie and its watershed as an example of a system in which there is a pressing need to resolve these uncertainties. In recent history, Lake Erie both suffered and recovered from serious eutrophication and related issues. More recently, however, there has been a resurgence of eutrophication and associated harmful algal blooms in Lake Erie, with symptoms reminiscent of prior eutrophication. This resurgence has led the USA and Canadian governments to commit to substantially reducing P inputs into Lake Erie in an effort to control eutrophication. We illustrate how key uncertainties about Lake Erie and its watershed contribute to challenges we face in restoring this ecosystem and propose avenues for their resolution. To this end, we contend that an ecosystem approach will be required for managing the eutrophication of freshwaters.
The quagga mussel (Dreissena rostriformis bugensis) is a filter-feeding invasive species that has re-engineered many freshwater ecosystems worldwide. High clearance rates (CRs) and dense populations ...underpin their ecological impacts. CRs, however, are highly variable, as are environmental factors that regulate them. Despite their widespread distribution in Europe and North America, knowledge of how multiple environmental factors regulate CRs of quagga mussels remains limited. We investigated quagga mussel CRs under varying conditions including water temperature, food availability, habitat depth, flow velocity, and duration of incubation in chambers with both static and flowing water. We found that CR was positively related to water temperature and initial food concentration in static chambers. When coupled with limited food concentration, cold water (7.5 °C), due to a deep-water upwelling event, produced very low CR (~ 10× lower) compared to warmer water (12–24 °C) (0.47 vs. 3.12–5.84 L g−1 DW h−1). Mussels from deeper water (20 m) had CRs that were ~ 3.5× higher than from shallower depths (2–10 m) and CRs were inversely affected by total mussel dry weight. Flow rates from 1 to 22 cm s−1 generated a unimodal pattern of CR with an optimal flow velocity of 6–12 cm s−1 (~ 2× higher than suboptimal CRs). Enhanced flow velocity (22 cm s−1), reflective of storm conditions in shallow waters, significantly increased the closing/reopening activity of mussel valves relative to lower velocities (1–12 cm s−1). Incubation time had a strong negative effect (~ 2–4× reduction) on CRs likely reflecting refiltration in static chambers versus food saturation of mussels in flowing chambers, respectively. Our findings highlight how multiple factors can influence quagga mussel CRs by factors of 2–10. Given widespread habitat heterogeneity in large aquatic ecosystems, whole-lake estimates of mussel impacts should include multiple regulatory factors that affect mussel filtration.
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•Filtering capacity of quagga mussels varied 2- to 10-fold under a range of conditions.•Water temperature and food concentration had positive effects on clearance rates.•Quagga mussels from deeper habitats filter water more rapidly.•Clearance rate demonstrates a unimodal pattern again flow velocity.•Whole-lake estimates of quagga mussel impacts must include these factors.
This study evaluated the effect of growth of different tissue compartments on the bioaccumulation of mercury (Hg) and polychlorinated biphenyls (PCBs) in Silver Carp (Hypophthalmichthys molitrix) and ...Bighead Carp (Hypophthalmichthys nobilis) from the Three Gorges Reservoir (TGR), China. A non-steady state bioenergetics/toxicokinetic model was developed to simulate PCB and Hg concentrations in these two species and compared with field data. Simulations using constant whole body growth rate and constant tissue to whole body weight ratios were contrasted against simulations adopting age specific whole body and tissue/age specific growth rates for their goodness of fit to field data. The simulations using age/tissue specific growth rates demonstrated better fit to field data for PCBs compared to the constant growth rate models (22% improved R2), while both models explained similar variation in Hg concentration data. Both species demonstrated higher growth rates of lipids (on a daily basis) relative to whole body and protein contributing to higher growth dilution of PCBs compared to Hg. Although stable isotope data indicated some degree of diet and/or habitat shift, simulations assuming a constant diet concentration explained between 36 and 40% of the variation in fish concentrations for both contaminants and fish species. This study demonstrates that differences in the bioaccumulation rate of PCBs and Hg by Asian carp can be partially explained by differences in the growth rates of key tissue storage compartments associated with each contaminant. These differences in chemical-specific growth dilution subsequently contribute to differences in chemical retention and bioaccumulation patterns of Hg and PCBs by fish.
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•Growth was a dominant process regulating the bioaccumulation of Hg and PCBs.•Specific tissue growth rate improved the accuracy for modelling Hg and PCBs in fish.•Lean dry protein% was normally constant, whereas lipid% exhibited higher variation.•The wider fluctuation in lipid growth can lead to higher variability in PCBs.
•A stratified random design was used to track temporal changes in sediment contamination.•Geospatial clustering provided a refined picture of local contaminated and clean zones.•Sediment ...contamination in the Detroit River remained stable over the past decade.
Concentrations of selected heavy metals (Cd, Cu, Hg, Pb, Zn) and organic contaminants (PCBs, PAHs) were investigated in samples from the Detroit River (Great Lakes, North America) in 1999 and 2008/09 collected using a stratified random sampling design. Getis–Ord geospatial analysis was used to further establish locations of areas demonstrating significantly high and low contaminant concentrations in the river. Based on the stratified random sampling design, a majority of the examined metals and organic contaminants demonstrated little or no trends with respect to regional sediment concentrations and river-wide mass balances over the investigated time interval. The Getis–Ord analysis revealed local scales of contaminated and clean areas which did not conform to the original strata used in the geostatistical sampling design. It is suggested that geospatial analyses such as Getis–Ord be used in the design of future sediment quality surveys to refine locations of strata that can simultaneously address sediment recovery over system-wide, regional and local spatial scales.
Accurate predictions on the bioaccumulation of persistent organic pollutants (POPs) are critical for hazard and ecosystem health assessments. Aquatic systems are influenced by multiple stressors ...including climate change and species invasions and it is important to be able to predict variability in POP concentrations in changing environments. Current steady state bioaccumulation models simplify POP bioaccumulation dynamics, assuming that pollutant uptake and elimination processes become balanced over an organism’s lifespan. These models do not consider the complexity of dynamic variables such as temperature and growth rates which are known to have the potential to regulate bioaccumulation in aquatic organisms. We contrast a steady state (SS) bioaccumulation model with a dynamic nonsteady state (NSS) model and a no elimination (NE) model. We demonstrate that both the NSS and the NE models are superior at predicting both average concentrations as well as variation in POPs among individuals. This comparison demonstrates that temporal drivers, such as environmental fluctuations in temperature, growth dynamics, and modified food-web structure strongly determine contaminant concentrations and variability in a changing environment. These results support the recommendation of the future development of more dynamic, nonsteady state bioaccumulation models to predict hazard and risk assessments in the Anthropocene.
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