Bacterial community composition in the Northern Gulf of Mexico intertidal sediment bioturbated by the ghost shrimp Lepidophthalmus louisianensis.

Bioturbation plays an important role in structuring microbial communities in coastal sediments. This study investigates the bacterial community composition in sediment associated with the ghost shrimp Lepidophthalmus louisianensis at two locations in the Northern Gulf of Mexico (Bay St. Louis, MS, and Choctawhatchee Bay, FL). Bacteria were analysed for shrimp burrows and for three different depths of bioturbated intertidal sediment, using second-generation sequencing of the 16S rRNA gene. Burrow walls held a unique bacterial community, which was significantly different from those in the surrounding sediment communities. Communities in burrow walls and surrounding sediment communities also differed between the two geographic locations. The burrow wall communities from both locations were more similar to each other than to sediment communities from same location. Alpha- and Gammaproteobacteria were more abundant in burrows and surface sediment than in the subsurface, whereas Deltaproteobacteria were more abundant in burrows and subsurface sediment, suggesting sediment mixing by the bioturbator. However, abundance of individual ASVs was geographic location-specific for all samples. Therefore, it is suggested that the geographic location plays an important role in regional microbial communities distinctiveness. Bioturbation appears to be an important environmental driver in structuring the community around burrows. Sampling was conducted during times of the year and water salinity, tidal regime and temperature were variable, nevertheless the structure microbial communities appeared to remain realatively stable suggesting that these environmental variable played only a minor role.

Comparisons Between Laboratory Sediment Toxicity Test Results and Assessment of Benthic Community Changes for a Lake with Mild Metal Contamination.

Effects of moderate-to-severe sediment contamination may be readily discernable in both sediment toxicity bioassays and benthic community assessments. However, the impact may be less obvious under conditions of relatively mild contamination and significant variation of natural environmental variables. This study evaluated sediment toxicity and benthic community impacts for a shallow eutrophic lake system with relatively low levels of sediment metal contamination. We evaluated selected sediment physical and chemical properties, as well as benthic community structure, for 50 sites along a sediment Pb contamination gradient in the lake. We tested the toxicity of sediment from 20 of the sites, using a standardized 42-days sediment bioassay with Hyalella azteca survival, reproduction, and growth endpoints. Using principal component and correlation analyses we found negative relationships for both Pb and Cu, between sediment metal concentrations and the diversity and abundance of benthic macroinvertebrates. Taxa known to be metal-sensitive (e.g., Hyalella sp. and Physa sp.) were less abundant at sites with relatively higher Pb and Cu concentrations. However, amphipod performance in the chronic toxicity test was not related to sediment Pb or Cu concentrations (but was influenced by sediment organic content). Our results demonstrate that an assessment of community-level effects may be warranted even when sediment metal concentrations are too low to elicit detectable toxic effects in standardized laboratory tests.

Feminization, altered gonadal development, and liver damage in least killifish (Heterandria formosa) exposed to sublethal concentrations of 17α-ethinylestradiol.

The widespread use of the synthetic estrogen 17 α-ethinylestradiol (EE2) has resulted in elevated levels in aquatic environments, where it is known to act as an endocrine disrupting chemical affecting fish and other aquatic organisms. Examining changes in the structure of the fish' gonads and liver has proven to be an effective approach for assessing these impacts. While changes have been reported for various fish species, it is not clear whether impacts are equally severe in live-bearing fishes. The present study looked at gonadal and liver development in EE2-exposed least killifish (Heterandria formosa), a live-bearing Poeciliid. Exposures to 0, 5, or 25 ng/L EE2 began within six days of birth and continued until fish became sexually mature 12-23 weeks later. Exposure to 5 ng/L EE2 resulted in severe intersex in fish with external male characteristics, a slowdown of spermatogenesis in these intersex fish and a slowdown of oogenesis in the female fish. Moreover, these fish had a variety of liver injuries. Fish exposed to 25 ng/L EE2 exhibited intersex but at a lower frequency than occurred at 5 ng/L. In contrast, liver damage and slowdown of both oogenesis and spermatogenesis exhibited the typical dose-dependence. These findings illustrate the importance of including histological analyses when assessing endocrine disruption in fish, demonstrate that the live-bearing mode of reproduction appears to provide limited protection from the effects of waterborne EE2, and provide further evidence that EE2 has multiple impacts on fish health and reproduction that are severe enough to potentially affect fish populations.

Impact of Long-Term Exposure to 17α-Ethinylestradiol in the Live-Bearing Fish Heterandria formosa.

17α-ethinylestradiol (EE2) is a potent synthetic estrogen that is routinely detected in aquatic ecosystems and exhibits estrogenic activity. Acute and chronic toxicity have been described for oviparous and ovoviviparous fish species; however, no information is available on the impacts of EE2 on viviparous, matrotrophic fish despite their ecological importance. The present study investigated the consequences of long-term EE2 exposure in the least killifish (Heterandria formosa). Effects on growth, time-to-sexual maturity, fecundity, and offspring survival were examined in an 8-month, life-cycle experiment. Starting as 0-6-day-old fish, least killifish were continuously exposed to EE2 at nominal concentrations of 0, 5, or 25 ng/L (measured concentrations averaged 0, 4.3, and 21.5 ng/L respectively). In the F0 generation, EE2-exposure did not affect survival but resulted in increased time-to-sexual maturity and a sex-dependent effect on size; female standard length was reduced while male standard length was increased. This caused the ordinarily larger females and smaller males to become more similar in size. Condition factor was reduced for both sexes. Fecundity was reduced by 50% and 75% at 5 and 25 ng/L EE2-exposure respectively. Continued EE2-exposure in the F1 generation resulted in significantly reduced survival. These results suggest that despite their matrotrophic development, these fish experience delayed development and reduced reproductive success from EE2-exposure and that effects appear to intensify in the second generation.

Accumulation, depuration dynamics and effects of dissolved hexavalent chromium in juvenile Japanese medaka (Oryzias latipes).

We previously demonstrated that chronic exposure to hexavalent chromium (Cr(VI)) causes a variety of adverse effects in the Japanese medaka (Oryzias latipes). The present study investigated the transition of acute to chronic effects by assessing the influences of Cr(VI) exposure concentration and exposure duration on Cr accumulation and their effects on fish growth and antioxidant physiology. Juvenile fish were exposed to 0.05, 0.5, 4 or 8mg/L Cr(VI) for 28 days. Endpoints were evaluated on days 3, 7, 14, 21 and 28. In addition, Cr depuration was examined for fish from two exposure groups (0.5 and 8mg/L). Chromium accumulation was rapid initially, then continued at a slower rate till the end of the exposure period without showing signs of reaching a steady state. Depuration patterns differed between the two exposure groups, but both reached 50% in 14 days. The rapid initial accumulation was accompanied by increased lipid peroxidation and elevated activities of antioxidants (e.g., GST, SOD and CAT). Activities of these enzymes had mostly returned to baseline levels by day 7, but there was no evidence of further cellular damage from ROS. Effects on fish length and weight continued to be evident over the 28-day exposure period. Our study suggest that the initial effects of Cr(VI) exposure may not be a good predictor of more-chronic effects in fish as a consequence of an efficient acclimation response by the antioxidant system that limits ROS-mediated toxicity.

The effect of sediment characteristics on bioturbation-mediated transfer of lead, in freshwater laboratory microcosms with Lumbriculus variegatus.

While it has been well established that sediment bioturbators can affect the fate of metals in aquatic systems and that the fate of metals there can depend on sediment characteristics, the interaction between these influences is not well known. The present study therefore investigated whether the influence of a sediment bioturbator on the fate of metals is affected by sediment characteristics. This was investigated using two laboratory microcosm experiments with lead-contaminated sediment and the oligochaete Lumbriculus variegatus. The first experiment used sediment collected from five Toledo Bend reservoir sites that differed in sediment characteristics, and analyses looked at the influence of sediment organic matter, sediment silt/clay content, sediment pH, and pore-water pH. In the second experiment, organic matter and silt/clay content of Toledo Bend reservoir sediment were varied experimentally using alpha-cellulose and clay, and Pb transfer to the water column and bioaccumulation were again quantified. Both experiments were conducted with sediment spiked with Pb to a concentration of 100 µg/g, at an oligochaete density of 6279 ind./m². In the first experiment, the Pb concentrations in the water column and those in the worms at the end of the 14-day experiment differed among sediment-collection sites. Silt/clay content and sediment pH were the two most important variables influencing Pb transfer from sediment to the water column. A multiple regression model with these variables explained 58% of the variability in this lead transfer. For Pb accumulation by the worms, sediment organic matter and pore-water pH were the two most important variables. This regression model explained 85% of the variability in tissue Pb levels. In the second experiment, where the individual effects of the organic matter and silt/clay content on Pb transport and distribution were assessed, the use of sediment with more organic matter resulted in a reduction in both the Pb transfer to the water column and the accumulation in worms. The increase in the sediment's silt/clay content resulted in a reduction in Pb bioaccumulation only. Overall, the results of the present study demonstrate that sediment pH, pore-water pH, organic matter, and silt/clay content influence the bioturbation-mediated transfer and the environmental distribution of Pb.

The effect of lead from sediment bioturbation by Lumbriculus variegatus on Daphnia magna in the water column.

The present study investigated the bioavailability and potential toxicity to Daphnia magna of lead released to the water column due to bioturbation by Lumbriculus variegatus. Experiments used microcosms with Pb-spiked sediment, with or without worms in the sediment, and with D. magna present in the water column. The daphniids were allowed free movement or were restricted to flow-through containers, in order to assess the influence of their direct contact with the contaminated sediment. A control group consisted of D. magna in clean moderately hard reconstituted water. At the end of the 12-day experiment, D. magna survival, reproduction, biomass, and Pb-bioaccumulation were determined. Water column turbidity and Pb levels were quantified to assess their influence on the Pb toxicity and bioaccumulation. The bioturbation by L. variegatus increased Pb levels and turbidity in the water column. While this resulted in an increased Pb bioaccumulation by the D. magna, the water column Pb levels and the Pb bioaccumulation were insufficient to bring about toxic effects for the survival, reproduction, and biomass of the daphniids. Contact of D. magna with the sediment resulted in an increase in their Pb bioaccumulation, with water turbidity and Pb data, suggesting that these crustaceans also acted as bioturbators. The increase in Pb bioaccumulation in D. magna as a consequence of bioturbation by L. variegatus demonstrates the potential for bioturbation to enhance contaminant toxicity to organisms in the water column, though this potential appeared relatively low in the case of lead.

Metal Concentrations in Sediment And Biota of the Huludao Coast in Liaodong Bay and Associated Human and Ecological Health Risks.

This study assessed the contamination extent and potential ecological and human health impacts for chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in sediments and indigenous benthic organisms along the coastal area of Huludao, China. We analyzed a total of eight species: two benthic fish species, two bivalves, two snails, and two decapod crustaceans. Cu, Zn, and Cd levels in sediment exceeded the Chinese marine sediment quality criteria. The geoaccumulation index was highest for Cd followed in a decreasing order by Zn, Pb, Cu, Ni, and Cr. Metal levels were highest in the four mollusk species. The oyster and veined rapa whelk had the highest bioaccumulation factors, indicating that these two species would be well suited for monitoring the metal pollution in this area. Our comparison of estimated daily intake values for human consumption of the seafood species to the Food and Agricultural Organization-recommended daily dietary allowances indicate potential health risks from the intake of Cd from all shellfish other than our crab species and Zn intake from oyster consumption. An analysis of target hazard quotients identified noncarcinogenic health risks from Cd (in all shellfish analyzed except for our crab species), Cu, and Zn (in oysters and veined rapa whelks). Moreover, an analysis of cancer risk from Pb ingestion detected an increased risk for consumption of all shellfish except for the crab species. Health risks seem especially pronounced for the consumption of oysters and the veined rapa whelks; a seafood advisory may be warranted for these mollusks.

Effects from a short-term exposure to copper or cadmium in gravid females of the livebearer fish (Gambusia affinis).

We investigated the reproductive effects of a 10-day maternal metal exposure in the live-bearing western mosquitofish. We exposed gravid females to 0.15µM copper or cadmium and monitored reproduction-related variables over the subsequent 8-month breeding season. Females gave birth to 1-5 broods, a number not affected by the exposure. Their first brood's size was reduced following exposure to either metal, while this effect was still evident for the second brood of copper-exposed females. Metal-exposed females also had more premature births, abortions, and broods containing dead offspring; these last two effects were still evident in second broods. The time-till-first-birth was reduced while the time-interval between first and second brood was increased in cadmium-exposed females, but not in copper-exposed ones. This study demonstrated that short-term metal exposure affects a variety of reproductive measures and that effects can still occur in broods that developed well after the end of the females' exposure.

Effects on life history variables and population dynamics following maternal metal exposure in the live-bearing fish Gambusia affinis.

This study investigated the effect of maternal copper and maternal cadmium exposure on life history variables and population dynamics in a live-bearing fish species. Gravid females were exposed to copper, cadmium, or background metal levels (control); maternal transfer of the metals was previously demonstrated using the exact same design. Each female's first brood, born after the exposure, was subdivided into two groups. One group was raised in the laboratory, to assess time-to and size-at sexual maturity, reproductive output and other life history variables. Offspring from the other group were used to start four mesocosm populations for each treatment. These populations were sampled monthly, for about 18 months, to assess population dynamics. For the laboratory-reared fish, offspring of copper-exposed females reached sexual maturity at a smaller size than did offspring from the other treatments. Maternal copper exposure and maternal cadmium exposure both resulted in fewer broods and an increase in gestation time. No impacts were detected for brood size, inter-brood interval, time-to-sexual-maturity, or life span. In the greenhouse population study, no effect of maternal copper or cadmium exposure was evident for population parameters, other than that the relative abundance of juveniles and/or newborns was reduced in populations established with offspring of the exposed females. This study provided evidence that a short-term metal exposure of gravid females can negatively affect their offspring's life history variables and potentially influence population dynamics in a life-bearing fish species.

Evidence for mild sediment Pb contamination affecting leaf-litter decomposition in a lake.

Much work has focused on the effects of metal-contaminated sediment on benthic community structure, but effects on ecosystem functions have received far less attention. Decomposition has been widely used as an integrating metric of ecosystem function in lotic systems, but not for lentic ones. We assessed the relationship between low-level sediment lead (Pb) contamination and leaf-litter decomposition in a lentic system. We measured 30-day weight loss in 30 litter-bags that were deployed along a Pb-contamination gradient in a cypress-forested lake. At each deployment site we also quantified macrobenthos abundance, dissolved oxygen, water depth, sediment organic content, sediment silt/clay content, and both total sediment and porewater concentrations of Cd, Cu, Ni, Pb and Zn. Principal components (PC) analysis revealed a negative relationship between Pb concentration and benthic macroinvertebrate abundance, and this covariation dominated the first PC axis (PC1). Subsequent correlation analyses revealed a negative relationship between PC1 and percent leaf-litter loss. Our results indicate that leaf-litter decomposition was related to sediment Pb and benthic macroinvertebrate abundance. They also showed that ecosystem function may be affected even where sediment Pb concentrations are mostly below threshold-effects sediment quality guidelines--a finding with potential implications for sediment risk assessment. Additionally, the litter-bag technique used in this study showed promise as a tool in risk assessments of metal-contaminated sediments in lentic systems.

Evidence of maternal copper and cadmium transfer in two live-bearing fish species.

We studied maternal transfer of an essential metal (copper) and a non-essential one (cadmium) in the live-bearing fishes Heterandria formosa and Gambusia affinis. The goals of this study were: (1) to determine whether metals are transferred from exposed females to their developing offspring; (2) to determine if this transfer differs between two fish species that differ in their degree of maternal provisioning during development; (3) to determine the duration of maternal metal transfer once females are no longer exposed; and (4) to determine whether copper and cadmium are transferred equivalently. We exposed gravid females to background levels (control) or 0.15 µM of metal for 10 days, and then transferred them to clean water. We allowed females to give birth to up to three broods, and then quantified metal levels in offspring born at least 3 days after the transfer. We detected maternal metal transfer for both metals and in both species. Offspring metal levels decreased as females spent more time in clean water. Similarly, metal levels were lower in later broods than in earlier ones. Maternal metal transfer was higher in H. formosa than in G. affinis. Our results constitute the first report of maternal metal transfer in live-bearing fishes, and show that developing embryos acquire both essential and non-essential metals from their mothers in both species. This shows that metal toxicity may be an issue for live-bearing fish in clean environments when the previous generation has encountered metal pollution.

The role of native salinity regime on grass shrimp (Palaemonetes pugio) sensitivity to cadmium.

In euryhaline crustaceans, sensitivity to toxic trace metals may be linked to osmoregulation and salinity conditions. This study investigated if grass shrimp (Palaemonetes pugio) populations from different salinity regimes differed in sensitivity to cadmium (Cd). Grass shrimp were collected in May 2011 from two marsh sites with average salinities of ~3.0 ppt and 24.0 ppt. Groups were acclimated for 3-32 weeks in either their respective native salinity (3.0 ppt → 3.0 ppt and 24.0 ppt → 24.0 ppt), or the average of the salinities of the two collection sites (3.0 ppt → 13.5 ppt and 24.0 ppt → 13.5 ppt). After acclimation, groups were exposed to equivalent free-ion Cd concentration (4.8 ± 0.3 mg/L, Cd(2+)) in their respective acclimated salinity to compare survival among salinity treatments. Results of Kaplan-Meier survival analysis indicated that 3.0 ppt → 3.0 ppt shrimp were more sensitive to Cd(2+) than any other group (p < 0.0001). Additionally, 3.0 ppt → 13.5 ppt shrimp were less sensitive to Cd(2+) than were 24.0 ppt → 13.5 ppt shrimp (p = 0.0013). These results suggest that sensitivity of grass shrimp to Cd is dependent upon the salinity during exposure, and the salinity regime from which the tested population originated. The implication is that toxicity studies and risk assessments using euryhaline crustaceans should consider the salinity of test population collection sites when interpreting and comparing results.

Quantitative genetics approaches to study evolutionary processes in ecotoxicology; a perspective from research on the evolution of resistance.

Quantitative genetic approaches are often used to study evolutionary processes in ecotoxicology. This paper focuses on the evolution of resistance to environmental contaminants-an important evolutionary process in ecotoxicology. Three approaches are commonly employed to study the evolution of resistance: (1) Assessing whether a contaminant-exposed population has an increased resistance relative to a control population, using either spatial or temporal comparisons. (2) Estimating a population's heritability of resistance. (3) Investigating responses in a laboratory selection experiment. All three approaches provide valuable information on the potential for contaminants to affect a population's evolutionary trajectory via natural selection. However, all three approaches have inherent limitations, including difficulty in separating the various genetic and environmental variance components, responses being dependent on specific population and testing conditions, and inability to fully capture natural conditions in the laboratory. In order to maximize insights into the long-term consequences of adaptation, it is important to not just look at resistance itself, but also at the fitness consequences and at correlated responses in characteristics other than resistance. The rapid development of molecular genetics has yielded alternatives to the "black box" approach of quantitative genetics, but the presence of different limitations and strengths in the two fields means that they should be viewed as complementary rather than exchangeable. Quantitative genetics is benefiting from the incorporation of molecular tools and remains an important field for studying evolutionary toxicology.

Heritability of heat tolerance in a small livebearing fish, Heterandria formosa.

Climate change is expected to result in an increased occurrence of heat stress. The long-term population-level impact of this stress would be lessened in populations able to genetically adapt to higher temperatures. Adaptation requires the presence of genetically-based variation. At-risk populations may undergo strong declines in population size that lower the amount of genetic variation. The objectives of this study were to quantify the heritability of heat tolerance in populations of the least killifish, Heterandria formosa, and to determine if heritabilities were reduced following a population bottleneck. Heritabilities of heat tolerance were determined for two lines of each of two source populations; two bottlenecked lines (established with one pair of fish) and two regular lines. Heat tolerance was quantified as temperature-at-death (TAD), when fish acclimated at 28 °C were subjected to an increase in water temperature of 2 °C/day. Mid-parent/mean offspring regressions and full-sib analyses were used to estimate the heritability of TAD. Heritability estimates from parent/offspring regressions ranged from 0.185 to 0.462, while those from sib analyses ranged from 0 to 0.324, with an overall estimate of 0.203 (0.230 for the regular lines, 0.168 for bottlenecked ones). Fish from the bottlenecked line from one source population (but not the other) had a lower heritability than did those from the regular line. These results show that the populations tested had some potential for adaptation to elevated water temperatures, and that this potential may be reduced following a population bottleneck. This should not be construed as evidence that natural populations will not suffer negative consequences from global warming; this study only showed that these specific populations have some potential to adapt under a very specific set of conditions.

A Mesocosm Assessment of the Effect of Bioturbation by the Ghost Shrimp (Lepidophthalmus louisianensis) on the Fate of Petroleum Hydrocarbons in the Intertidal Zone.

To fully assess the long-term impacts of oil spills like the 2010 Deepwater Horizon incident in the northern Gulf of Mexico, the potential for organisms other than microbes to affect the fate and distribution of the oil may have to be considered. This influence could be substantial for abundant bioturbating benthic animals like the ghost shrimp Lepidophthalmus louisianensis. An assessment of the influence of these ghost shrimp on petroleum hydrocarbons was conducted in laboratory micro- and mesocosms containing coastal Gulf of Mexico sediment, seawater, and oil or the polynuclear aromatic hydrocarbon (PAH) pyrene. In an experiment with pyrene added to the water column, the ghost shrimp presence lowered water-column pyrene concentrations. In an experiment with oil added to the sediment surface, the ghost shrimp presence decreased PAH concentrations in the sediment surface layer but increased these in the water column and subsurface sediment. A companion study and a mass-balance analysis indicated a net loss of PAHs through an enhancement of microbial degradation. In an experiment in which oil was added as a narrow subsurface layer in the sediment, the ghost shrimp presence appeared to broaden the oil's depth distribution. Taken together, these results demonstrate that ghost shrimp can significantly influence the biodegradation and distribution of spilled oil in coastal ecosystems. Environ Toxicol Chem 2020;39:637-647. © 2019 SETAC.

Digestive solubilization of Cd in highly-contaminated sediment by marine deposit feeders: The roles of intestinal surfactants in Cd mobilization and Re-Adsorption processes.

Marine deposit feeders are of ecological significance in transferring sedimentary Cd along aquatic food chains. A key process for this transfer is these organisms' dietary uptake of Cd via solubilization of Cd present in ingested contaminated sediment. To better understand the bioavailability of sedimentary Cd to deposit feeders, the present study used in vitro extraction experiments to explore the contribution of different digestive agents (proteins, amino acids and surfactants) to the solubilization of Cd from sediment collected in a highly-contaminated Chinese bay. This was done for various commercially-available mimetic digestive agents (the protein BSA, a mixture of amino acids, and the surfactants rhamnolipid and SDS), and for proteins and surfactants collected from the gut juice of a sipunculan worm. The Cd mobilization capacity of BSA was significantly higher than that of the amino acids and the commercial surfactants. In the presence of BSA, > 70% of the released Cd became associated with this protein. In contrast, the digestive proteins from the sipunculan had a lower Cd mobilization capacity than was the case for the other digestive agents and the majority of the released Cd (∼80%) was associated with small molecular weight fractions. The differences in Cd mobilization between the BSA and the digestive proteins were attributed to differences in their sediment-adsorption tendencies and their Cd-complexing capacities. While the digestive surfactants had minor effects on the release of sedimentary Cd, they significantly enhanced Cd mobilization by the digestive proteins when both were present simultaneously. Our results suggest that the characteristics of proteins should be considered when using commercially-available mimetic digestive agents to explore Cd bioavailability in sediments. Furthermore, digestive surfactants seem to have important effects on the solubilization of Cd during gut passage by reducing the adsorption of the digestive proteins to the sediments.

Digestive solubilization of particle-associated arsenate by deposit-feeders: The roles of proteinaceous and surfactant materials.

Solubilization of arsenate in guts of deposit-feeders is a key process for their dietary uptake of arsenate from contaminated sediments. The present study explored this digestive solubilization with in vitro extraction experiments that quantified arsenic (As) release from substrates (natural sediment and As-enriched iron oxides) in the presence of various digestive agents (proteins, amino acids and surfactants collected from gut fluid of a sipunculan worm). To investigate potential mechanisms for the influence of digestive agents, analyses determined correlations between As and Fe concentrations, the size distribution of the As bound to the digestive agents, and the adsorption of the digestive agents on the substrates. Both the digestive surfactants and proteinaceous materials increased arsenate mobilization, with the surfactants enhancing the effects of the proteinaceous materials. Arsenate reduction and reductive dissolution of iron oxides were not observed and correlations between the concentrations of released As and Fe were weak. These findings indicate that dissolution release of Fe did not appear to be the main route by which the digestive agents mobilized particle-associated As. Most of the released As (>70%) was distributed in the <10 kDa fraction of the digestive agents, showing that the As mobilization was also not caused by complexation with proteins in the digestive agents. In contrast, adsorption of the digestive agents occurred along with the release of arsenate from the arsenate-rich substrates, suggesting that competitive adsorption was the mechanism by which the digestive agents mobilized sedimentary arsenate. Our work demonstrated that the presence of digestive surfactants significantly enhances arsenate availability during deposit feeding.

Crude oil toxicity to fiddler crabs (Uca longisignalis and Uca panacea) from the northern Gulf of Mexico: Impacts on bioturbation, oxidative stress, and histology of the hepatopancreas.

The intensive drilling and extraction of fossil fuels in the Gulf of Mexico result in a considerable risk of oil spills impacting its coastal ecosystems. Impacts are more likely to be far-reaching if the oil affects ecosystem engineers like fiddler crabs, whose activities modify biogeochemical processes in the sediment. The present study investigated effects of oil on the fiddler crabs Uca longisignalis and Uca panacea, which are important as ecosystem engineers and as prey for a wide variety of species. The present study used mesocosms and microcosms to investigate the effects of crude oil on fiddler crab burrowing and to assess cellular and tissue damage by the oil. Fiddler crabs were exposed for periods of 5 or 10 d to oil concentrations up to 55 mg/cm2 on the sediment surface. Their burrowing was delayed, their burrows were smaller, and they transported less sediment in the presence of oil. The hepatopancreas had elevated levels of oxidative stress and a higher abundance of blister cells, which play a role in secretory processes. Interspecific differences were observed; most effects were strongest in U. panacea, though burrowing was more strongly affected in U. longisignalis. The present study demonstrates that crude oil is likely to impact fiddler crabs and many species that depend on them for their diet or for the ecological changes that result from their burrowing. Environ Toxicol Chem 2018;37:491-500. © 2017 SETAC.

Laboratory culturing and selection for increased resistance to cadmium reduce genetic variation in the least killifish, Heterandria formosa.

Populations exposed to environmental contaminants can undergo intense selection pressures, which in turn can lead to a loss of genetic variation. We assessed this loss of genetic variation in the least killifish Heterandria formosa for laboratory populations that had undergone eight generations of selection for an increased resistance to cadmium. Using microsatellite markers, we compared genetic variation between three selection and three control laboratory populations and between these laboratory populations and the source population. Heterozygosity was lower in each selection population than it was in its paired control population, with this difference being statistically significant in two of the three comparisons. This is evidence that adaptation to environmental contaminants can result in an overall loss of genetic variation. Furthermore, the laboratory populations had much lower heterozygosity than did the source population. The latter loss of genetic variation, probably a result of random drift, did not prevent the laboratory populations from showing a strong response to the selection for cadmium resistance. The loss of genetic variation resulting from maintaining populations in the laboratory demonstrates that it is important to maintain a large population size for such populations and that the potential for loss of genetic variation in laboratory populations is taken into consideration in ecotoxicology when extrapolating from laboratory to natural populations.