Freshwater fauna are particularly sensitive to environmental change and disturbance. Management agencies frequently use fish and amphibian biodiversity as indicators of ecosystem health and a way to ...prioritize and assess management strategies. Traditional aquatic bioassessment that relies on capture of organisms via nets, traps and electrofishing gear typically has low detection probabilities for rare species and can injure individuals of protected species. Our objective was to determine whether environmental DNA (eDNA) sampling and metabarcoding analysis can be used to accurately measure species diversity in aquatic assemblages with differing structures. We manipulated the density and relative abundance of eight fish and one amphibian species in replicated 206‐L mesocosms. Environmental DNA was filtered from water samples, and six mitochondrial gene fragments were Illumina‐sequenced to measure species diversity in each mesocosm. Metabarcoding detected all nine species in all treatment replicates. Additionally, we found a modest, but positive relationship between species abundance and sequencing read abundance. Our results illustrate the potential for eDNA sampling and metabarcoding approaches to improve quantification of aquatic species diversity in natural environments and point the way towards using eDNA metabarcoding as an index of macrofaunal species abundance.
Ionic liquids (ILs) are salts that remain liquid down to low temperatures, and sometimes well below room temperature. ILs have been called "green solvents" because of their extraordinarily low vapor ...pressure and excellent solvation power, but ecotoxicology studies have shown that some ILs exhibit greater toxicity than traditional solvents. A fundamental understanding of the molecular mechanisms responsible for IL toxicity remains elusive. Here we show that one mode of IL toxicity on unicellular organisms is driven by swelling of the cell membrane. Cytotoxicity assays, confocal laser scanning microscopy, and molecular simulations reveal that IL cations nucleate morphological defects in the microbial cell membrane at concentrations near the half maximal effective concentration (EC50) of several microorganisms. Cytotoxicity increases with increasing alkyl chain length of the cation due to the ability of the longer alkyl chain to more easily embed in, and ultimately disrupt, the cell membrane.
Species richness is a metric of biodiversity that represents the number of species present in a community. Traditional fisheries assessments that rely on capture of organisms often underestimate true ...species richness. Environmental DNA (eDNA) metabarcoding is an alternative tool that infers species richness by collecting and sequencing DNA present in the ecosystem. Our objective was to determine how spatial distribution of samples and “bioinformatic stringency” affected eDNA-metabarcoding estimates of species richness compared with capture-based estimates in a 2.2 ha reservoir. When bioinformatic criteria required species to be detected only in a single sample, eDNA metabarcoding detected all species captured with traditional methods plus an additional 11 noncaptured species. However, when we required species to be detected with multiple markers and in multiple samples, eDNA metabarcoding detected only seven of the captured species. Our analysis of the spatial patterns of species detection indicated that eDNA was distributed relatively homogeneously throughout the reservoir, except near the inflowing stream. We suggest that interpretation of eDNA metabarcoding data must consider the potential effects of water body type, spatial resolution, and bioinformatic stringency.
Room‐temperature ionic liquids (ILs) are considered to be green chemicals that may replace volatile organic solvents currently used by industry. However, IL effects on aquatic organisms and ...ecosystems are currently unknown. We studied the acute effects of imidazolium‐based ILs on survival of the crustacean Daphnia magna and their chronic effects on number of first‐brood neonates, total number of neonates, and average brood size. Lethal concentrations of imidazolium ILs with various anions (X−) ranged from a median lethal concentration (LC50) of 8.03 to 19.91 mg L−1, whereas salts with a sodium cation (Na+ X−) were more than an order of magnitude higher (NaPF6 LC50, 9,344.81 mg L−1; NaBF4 LC50, 4765.75 mg L−1). Thus, toxicity appeared to be related to the imidazolium cation and not to the various anions (e.g., CI−, Br−, PF−6, and BF−4). The toxicity of imidazolium‐based ILs is comparable to that of chemicals currently used in manufacturing and disinfection processes (e.g., ammonia and phenol), indicating that these green chemicals may be more harmful to aquatic organisms than current volatile organic solvents. We conducted 21‐d chronic bioassays of individual D. magna exposed to nonlethal IL concentrations at constant food‐resource levels. Daphnia magna produced significantly fewer total neonates, first‐brood neonates, and average neonates when exposed to lower concentrations (0.3 mg L−1) of imidazolium‐based ILs than in the presence of Na‐based salts at higher concentrations (400 mg L−1). Such reductions in the reproductive output of Daphnia populations could cascade through natural freshwater ecosystems. The present study provides baseline information needed to assess the potential hazard that some ILs may pose should they be released into freshwater ecosystems.
Pacific salmon (Oncorhynchus spp.) disturb sediments and fertilize streams with marine-derived nutrients during their annual spawning runs, leading researchers to classify these fish as ecosystem ...engineers and providers of resource subsidies. While these processes strongly influence the structure and function of salmon streams, the magnitude of salmon influence varies widely across studies. Here, we use meta-analysis to evaluate potential sources of variability among studies in stream ecosystem responses to salmon. Results obtained from 37 publications that collectively included 79 streams revealed positive, but highly inconsistent, overall effects of salmon on dissolved nutrients, sediment biofilm, macroinvertebrates, resident fish, and isotopic enrichment. Variation in these response variables was commonly influenced by salmon biomass, stream discharge, sediment size, and whether studies used artificial carcass treatments or observed a natural spawning run. Dissolved nutrients were positively related to salmon biomass per unit discharge, and the slope of the relationship for natural runs was five to ten times higher than for carcass additions. Mean effects on ammonium and phosphorus were also greater for natural runs than carcass additions, an effect attributable to excretion by live salmon. In contrast, we observed larger positive effects on benthic macroinvertebrates for carcass additions than for natural runs, likely because disturbance by live salmon was absent. Furthermore, benthic macroinvertebrates and biofilm associated with small sediments (<32 mm) displayed a negative response to salmon while those associated with large sediments (>32 mm) showed a positive response. This comprehensive analysis is the first to quantitatively identify environmental and methodological variables that influence the observed effects of salmon. Identifying sources of variation in salmon-stream interactions is a critical step toward understanding why engineering and subsidy effects vary so dramatically over space and time, and toward developing management strategies that will preserve the ecological integrity of salmon streams.
Room‐temperature ionic liquids (ILs) are being promoted as environmentally friendly alternatives to volatile organic solvents currently used by industry. Because ILs are novel and not yet in ...widespread use, their potential impact on aquatic organisms is unclear. We studied the effects of several ILs on the survivorship and behavior (movement and feeding rates) of the freshwater pulmonate snail, Physa acuta. Median lethal concentrations (LC50s) of ILs with imidazolium‐ and pyridinium‐based cations and Br− and PF−6 as anions ranged from 1 to 325 mg/L. Toxicity was greatest for ILs with eight‐carbon alkyl chains attached to both imidazolium and pyridinium rings and declined with shorter alkyl chains, indicating a positive relationship between alkyl chain length and toxicity. Compared to controls, snails moved more slowly when exposed to butyl‐ and hexyl‐cation ILs at 1 to 3% of LC50 concentrations but were not affected at higher IL concentrations (4–10% of LC50), which is characteristic of U‐shaped dose‐response curves. Snail movement was not affected by ILs with octyl alkyl groups. Grazing patterns, however, indicated that snails grazed less at higher IL concentrations. Physa acuta egestion rates were reduced in the presence of ILs at 3 to 10% of LC50 concentrations. Thus, nonlethal IL concentrations affected P. acuta behaviors, potentially impacting individual fitness and food web interactions. These results provide initial information needed to assess the potential hazards of ILs should they reach freshwater ecosystems.
Wetlands are the largest natural source of methane (CH4) emissions to the atmosphere, which vary along salinity and productivity gradients. Global change has the potential to reshape these gradients ...and therefore alter future contributions of wetlands to the global CH4 budget. Our study examined CH4 production along a natural salinity gradient in fully inundated coastal Alaska wetlands. In the laboratory, we incubated natural sediments to compare CH4 production rates between non-tidal freshwater and tidal brackish wetlands, and quantified the abundances of methanogens and sulfate-reducing bacteria in these ecosystems. We also simulated seawater intrusion and enhanced organic matter availability, which we predicted would have contrasting effects on coastal wetland CH4 production. Tidal brackish wetlands produced less CH4 than non-tidal freshwater wetlands probably due to high sulfate availability and generally higher abundances of sulfate-reducing bacteria, whereas non-tidal freshwater wetlands had significantly greater methanogen abundances. Seawater addition experiments with freshwater sediments, however, did not reduce CH4 production, perhaps because the 14-day incubation period was too short to elicit a shift in microbial communities. In contrast, increased organic matter enhanced CH4 production in 75 % of the incubations, but this response depended on the macrophyte species added, with half of the species treatments having no significant effect. Our study suggests that CH4 production in coastal wetlands, and therefore their overall contribution to the global CH4 cycle, will be sensitive to increased organic matter availability and potentially seawater intrusion. To better predict future wetland contributions to the global CH4 budget, future studies and modeling efforts should investigate how multiple global change mechanisms will interact to impact CH4 dynamics.
Pacific salmon transfer large quantities of material to tributaries during their spawning migrations, including carcass tissue and labile nutrients but also persistent organic pollutants (POPs) and ...heavy metals. We conducted a Before-After-Control-Intervention experiment by adding salmon carcasses and eggs to a Michigan (USA) stream that had never received inputs from non-native salmon to understand the bioaccumulation and persistence of biotransported contaminants. Our experimental outcomes were compared to previous studies using meta-analysis. Coincident with the introduction of salmon, the PCB and DDE burden of resident trout significantly increased. However, we did not observe changes in total mercury (Hg). Two years after the salmon addition experiment concluded, resident trout POP concentrations had returned to pre-addition levels, with no difference between the treatment and control reaches. Analysis of effect sizes suggested that the contaminant response observed in our experiment is consistent with field survey observations. Our study suggested that the consumption of salmon eggs drove the increase in POP burden of resident trout while Hg bioaccumulation was influenced by watershed sources. Critically, our study suggests that ecosystems are capable of quickly recovering from POP inputs from species migrations if contaminant sources are removed.
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•Pacific salmon transfer organic contaminants to resident biota during their spawning migrations.ir organic contaminants.to•An experimental salmon addition led to increases in POPs, but no change in Hg in stream resident trout.•POPs returned to background concentrations two-years after the salmon addition.•Consumption of salmon eggs likely drives bioaccumulation of POPs in stream resident trout.
The foundation for any ecological study and for the effective management of biodiversity in natural systems requires knowing what species are present in an ecosystem. We assessed fish communities in ...a stream using two methods, depletion‐based electrofishing and environmental DNA metabarcoding (eDNA) from water samples, to test the hypothesis that eDNA provides an alternative means of determining species richness and species identities for a natural ecosystem. In a northern Indiana stream, electrofishing yielded a direct estimate of 12 species and a mean estimated richness (Chao II estimator) of 16.6 species with a 95% confidence interval from 12.8 to 42.2. eDNA sampling detected an additional four species, congruent with the mean Chao II estimate from electrofishing. This increased detection rate for fish species between methods suggests that eDNA sampling can enhance estimation of fish fauna in flowing waters while having minimal sampling impacts on fish and their habitat. Modern genetic approaches therefore have the potential to transform our ability to build a more complete list of species for ecological investigations and inform management of aquatic ecosystems.
The foundation for any ecological study and the effective management of biodiversity in natural systems requires knowing what species are present in an ecosystem. Using environmental DNA and metabarcoding techniques to assess the fish species present in a stream environment, we demonstrate molecular techniques can identify all 12 species captured by traditional means along with four additional species not captured. This increased detection rate for fish species between methods suggests that eDNA sampling can enhance estimation of fish fauna in flowing waters while having minimal sampling impacts on fish and their habitat.
We measured perfluoroalkyl substances (PFAS) in prey and predator fish from Lake Michigan (USA) to investigate the occurrence and biomagnification of these compounds in this important ecosystem. ...Twenty-one PFAS were analyzed in 117 prey fish obtained from sites across Lake Michigan and in 87 salmonids collected in four lake quadrants. The mean concentration of sum (∑) PFAS above the method detection limit was 12.7 ± 6.96 ng g−1 wet weight in predator fish (all of which were salmonids) and 10.7 ± 10.4 ng g−1 in prey fish, with outlier levels found in slimy sculpin, Cottus cognatus (187 ± 12.2 ng g−1 ww). Perfluorooctanoic sulfonic acid (PFOS) was the most frequently detected and most abundant compound of the 21 PFAS, occurring in 98 % of individuals with a mean concentration of 9.86 ± 6.36 ng g−1 ww without outliers. Perfluoroalkyl carboxylates (PFCA) concentrations were higher in prey fish than in predators, with some compounds such as perfluorooctanoic acid (PFOA) being detected in higher frequency in prey fish. Besides PFOS, detection of several long-chain (C8-C12) PFCAs were observed in >80 % of the prey fish. Overall, the observed concentrations in Lake Michigan fish were lower than those reported in other Laurentian Great Lakes except for Lake Superior. Biomagnification factors (BMFs) for PFOS exceeded 1.0 (range, 1.80 to 5.12) in all predator-prey relationships analyzed, indicating biomagnification of these compounds, whereas BMFs of other long-chain PFCAs varied according to the fish species. PFAS were found in all fish species measured from Lake Michigan and commonly biomagnified from prey to predator fish, strongly suggesting a dietary connection.
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•PFAS were found in all analyzed fish species from Lake Michigan.•PFOS was the dominant compound found in Lake Michigan fishes.•PFAS accumulation varied in salmonids across Lake Michigan.•Benthic sculpins had higher concentrations of PFAS than other Lake Michigan fishes.•Long-chain PFAS biomagnified from prey to predator fish.
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