Olfactory Sampling Recovery Following Sublethal Copper Exposure in the Rusty Crayfish, Orconectes rusticus

Copper-Induced Chemosensory Impairment is Reversed by a Short Depuration Period in Northern Clearwater Crayfish (Faxonius propinquus)

Crayfish rely on their chemosensory system for many essential behaviours including finding food, finding mates, and to recognize individuals. Copper can impair chemosensation in crayfish at low concentrations; however, it is not clear if the effect is ameliorated once copper is removed. To better understand the effect of and recovery from copper exposure in crayfish, we exposed Northern clearwater crayfish (Faxonius propinquus) to 31.3 [Formula: see text] copper for 24 h and measured the response of the crayfish to a food cue. The crayfish were then placed into clean water to depurate for an 24 h. The results demonstrated that the crayfish did not respond to a food cue if they had been exposed to copper, but showed a full response after a 24 h recovery period without copper. Higher concentrations of copper have shown a much longer-term effect in rusty crayfish (Faxonius rustics), indicating there is a concentration where the copper is causing longer-term damage instead of just impairing chemosensation. These results highlight the fact that even though contaminants like copper can have profound effects at low concentrations, by removing the contaminants the effect can be ameliorated.

Post-exposure Period as a key Factor to Assess Cadmium Toxicity: Lethal vs. Behavioral Responses

The exposure of animals to pollution in ecosystems is not always chronic. Toxicants can remain in aquatic ecosystems for a short-term. To improve the extrapolation of laboratory results to natural scenarios the inclusion of post-exposure periods is a relevant issue. The present study focuses on the assessment of cadmium toxicity on survival and behavior of the aquatic snail Potamopyrgus antipodarum (Tateidae, Mollusca) during exposure and post-exposure. Animals were exposed for 48 h to cadmium (0.05, 0.14, 0.44 and 1.34 mg Cd/L) and 168 h of post-exposure. During the post-exposure period an increase in mortality in all concentrations was observed. The effects observed during the post-exposure period on the LC50 and EC50 were significant. During the post-exposure, behavior showed a clear recovery in surviving animals exposed to 0.44 mg Cd/L. Animals exposed to 0.05 mg Cd/L did not show differences with control. Therefore, mortality after exposure should be included in the ecotoxicological bioassays for a more realistic estimation of the cadmium effects. To assess the degree of animal recovery after cadmium exposure, behaviour has been shown as an adequate parameter.

Behavioral Variables to Assess the Toxicity of Unionized Ammonia in Aquatic Snails: Integrating Movement and Feeding Parameters

Behavioral endpoints are important parameters to assess the effects of toxicants on aquatic animals. These endpoints are useful in ecotoxicology because several toxicants modify the animal behavior, which may cause adverse effects at higher levels of ecological organization. However, for the development of new bioassays and for including the behavior in ecotoxicological risk assessment, the comparison of sensitivity between different behavioral endpoints is necessary. Additionally, some toxicants remain in aquatic environments for a few hours or days, which may lead to animal recovery after toxicant exposure. Our study aimed to assess the effect of unionized ammonia on the movement and feeding behaviors of the aquatic gastropod Potamopyrgus antipodarum (Tateidae, Mollusca) and its recovery after exposure. Four treatments were used: a control and three nominal concentrations of unionized ammonia (0.25, 0.5 and 1 mg N-NH₃/L). Each treatment was replicated eight times, with six animals in each replicate. Animals were exposed to unionized ammonia for 48 h (exposure period) and, subsequently, to control water for 144 h (post-exposure period). Two movement variables were monitored without food and five feeding behavioral variables were monitored in the presence of food. Some of the feeding behavioral variables showed higher sensitivity (LOEC = 0.25-0.5 mg N-NH₃/L) than the movement behavior variables monitored without food (LOEC = 1 mg N-NH₃/L). After exposure to unionized ammonia, animals showed a recovery of most behavioral endpoints. The inclusion of post-exposure period and feeding behaviors in bioassays may make studies more realistic, which is crucial for a proper ecotoxicological risk assessment.

Toxicological mechanism of excessive copper supplementation: Effects on coloration, copper bioaccumulation and oxidation resistance in mud crab Scylla paramamosain

Copper is a widespread pollutant in marine environments, and marine animals can ingest large amounts of copper through the food chain. Here, an 8-week feeding trial was designed to investigate the effects of different dietary copper levels on coloration, copper bioaccumulation, stress response and oxidation resistance of juvenile mud crab Scylla paramamosain. The results indicated that crabs fed the diet with 162 mg/kg copper exhibited a dark-blue carapace and hemolymph. The accumulation of copper in tissues was positively correlated with the level of copper in feed. High/excess dietary copper (162 mg/kg) up-regulated the expression of stress response related genes, and reduced the expression/activities of anti-oxidation genes/enzymes. The activity of phenoloxidase decreased significantly when dietary copper level was 86-162 mg/kg, and the expression of hemocyanin was up-regulated in crab fed the diets with 28-162 mg/kg copper. Overall, the results of the present study indicated that high dietary copper led to parachrea in carapace and hemolymph of mud crab, and caused copper deposition abnormality in carapace and hepatopancreas. The data suggested that the toxic effects of dietary copper were concentration-dependent such that, excess dietary copper (162 mg/kg) had adverse impacts on oxidation resistance.

No detectable changes in crayfish behavior due to sublethal dietary mercury exposure

Mercury, and particularly its organic form, methylmercury (MeHg), is a ubiquitous environmental contaminant with documented dosage-dependent adverse effects on endpoints spanning many levels of biological organization. However, relatively little is known about the sublethal impacts of environmentally-relevant exposures on behavioral characteristics that may impact predator-prey relationships, and thus the potential for Hg bioaccumulation within food webs due to behavioral impairments. This study investigated the potential for dietary mercury exposure to impair two behavioral outcomes in the highly invasive rusty crayfish, Faxonius rusticus, which are expected to influence interactions with their fish predators: the tail-flip escape response and chelae pinch strength. Field-caught animals were randomly assigned to four dietary treatments with mean (±1 SE) dry-weight total Hg (THg) concentrations of 3.52 ± 0.57, 114.01 ± 4.05, 274.10 ± 0.38, and 565.79 ± 1.33 ng/g in the control, low, moderate and high exposure treatments, respectively, for 16 weeks. After initial observations, exposures began and mass and behavior were measured every two weeks. At the end of the experiment, THg concentrations in tail muscle tissue were significantly higher in the high exposure treatment than in the control and low exposure treatments (Tukey's HSD, family-wise α = 0.05). Exposure-dependent declines in survival, mass, pinch strength, or tail-flip escape response velocity were not detected within the 12- to 16-week experimental exposure period, which represents one season of the crayfish's 3-4 year lifespan. This suggests that crayfish may be relatively tolerant of dietary exposure to sublethal concentrations of mercury within a single season. Further investigation of the physiological underpinnings of this tolerance is warranted.

Bt Proteins Exacerbate Negative Growth Effects in Juvenile Rusty (F. rusticus) Crayfish Fed Corn Diet

The adoption of genetically modified (GM) crops has occurred rapidly in the United States. The transfer of GM corn byproducts from agricultural fields to nearby streams after harvest is significant and occurs well into the post-harvest year. These corn leaves, stems, and cobs then become a detrital food source for organisms, such as shredders in the stream ecosystem. Considering that the nontarget effects of Bt corn have been observed in some terrestrial organisms, we assessed whether Bt toxins affect an important aquatic organism, juvenile F. rusticus crayfish. Juvenile crayfish were fed six distinct diet treatments: two varieties of Bt corn, two non-Bt controls of herbicide tolerant corn, and two controls: fish gelatin and river detritus. Juveniles were fed these diets while housed in flow-through artificial streams that received natural stream water from a local source. Specific growth rate and survivorship of the crayfish were measured throughout the study. Juveniles fed corn diets grew significantly less and had reduced survival compared with juveniles fed fish gelatin or river detritus diets. Furthermore, juveniles fed one Bt variety of corn (VT Triple Pro^®) exhibited significantly less growth than those fed one of the herbicide tolerant varieties (Roundup Ready 2^®). Our study shows that corn inputs to streams may be detrimental to the growth and survivorship of juvenile crayfish and that certain Bt varieties may exacerbate these negative effects. These effects on crayfish will have repercussions for the entire ecosystem, because crayfish are conduits of energy between many trophic levels.

Protectiveness of Cu water quality criteria against impairment of behavior and chemo/mechanosensory responses: An update

A meta-analysis was conducted of studies that reported behavior and chemo/mechanosensory responses by fish, amphibians, and aquatic invertebrates in Cu-containing waters and also reported sufficient water chemistry for calculation of hardness-based and biotic ligand model (BLM)-based water quality criteria (WQC) for Cu. The calculated WQC concentrations were then compared with the corresponding 20% impairment concentrations (IC20) of Cu for those behavior and chemo/mechanosensory responses. The hardness-based acute and chronic WQC for Cu would not have been protective (i.e., the IC20 would have been lower than the WQC) in 33.6 and 26.2%, respectively, of the 107 combined behavior- and chemo/mechanosensory-response cases that also had adequate water chemistry data for BLM-based WQC calculations (32.7% inconclusive). In comparison, the BLM-based acute and chronic WQC for Cu would not have been protective in only 10.3 and 4.7%, respectively, of the same 107 cases (29.9% inconclusive). To improve evaluations of regulatory effectiveness, researchers conducting aquatic Cu toxicity tests should measure and report complete BLM-input water chemistry and bracket the hardness-based and BLM-based WQC concentrations for Cu that would be applicable in their exposure waters. This meta-analysis demonstrates that, overall, the BLM-based WQC for Cu were considerably more protective than the hardness-based WQC for Cu against impairment of behavior and chemo/mechanosensory responses. Environ Toxicol Chem 2018;37:1260-1279. © 2018 SETAC.

Comparative Study of Chemosensory Organs of Shrimp From Hydrothermal Vent and Coastal Environments

The detection of chemical signals is involved in a variety of crustacean behaviors, such as social interactions, search and evaluation of food and navigation in the environment. At hydrothermal vents, endemic shrimp may use the chemical signature of vent fluids to locate active edifices, however little is known on their sensory perception in these remote deep-sea habitats. Here, we present the first comparative description of the sensilla on the antennules and antennae of 4 hydrothermal vent shrimp (Rimicaris exoculata, Mirocaris fortunata, Chorocaris chacei, and Alvinocaris markensis) and of a closely related coastal shrimp (Palaemon elegans). These observations revealed no specific adaptation regarding the size or number of aesthetascs (specialized unimodal olfactory sensilla) between hydrothermal and coastal species. We also identified partial sequences of the ionotropic receptor IR25a, a co-receptor putatively involved in olfaction, in 3 coastal and 4 hydrothermal shrimp species, and showed that it is mainly expressed in the lateral flagella of the antennules that bear the unimodal chemosensilla aesthetascs.

The Degree of Impairment of Foraging in Crayfish (Orconectes virilis) due to Insecticide Exposure is Dependent upon Turbulence Dispersion

As toxicants move into aquatic systems, the concentration at any point in space or time is heavily influenced by the flow dynamics. The dispersion of these chemicals creates a toxicant concentration that fluctuates widely in time and is highly dependent on the spatial heterogeneity of turbulence. Despite this knowledge on the movement of toxicants in natural systems, most ecotoxicological studies use static exposure paradigms that ignore the spatio-temporal dynamics of toxicants in aquatic systems. Although recent studies have begun to use pulsed paradigms in an attempt to mimic natural conditions, the heterogeneity of real concentrations in natural systems rarely is considered for use in these tests. Thus, understanding how organisms are impaired by naturally distributed toxicants is relatively unknown. The purpose of this experiment was to determine how turbulent dispersion of a toxicant negatively impacts a behavioral task and if altering the nature of turbulence will change the negative impact of the toxicant. Crayfish were exposed to a turbulent plume of carbaryl, an insecticide, under two different turbulent conditions and two different spatial conditions. Turbulence was altered by placing an obstruction within the flow which mimics a natural obstruction in lentic systems. Crayfish were exposed to sublethal concentrations of carbaryl for 48 h under these different dynamic conditions. After toxicant exposure, crayfish foraging ability was measured in a flow-through Y maze. We hypothesized that crayfish exposed to the toxicant under more turbulent conditions would exhibit more detrimental responses due to the increased variation in chemical fluctuations. The fine-scale chemical distribution of the toxicant and the three-dimensional velocity profile were characterized for each of the turbulent conditions and each of the spatial locations. Analyses of these data showed that changes in turbulence or spatial location created a unique exposure condition. Particularly, significant variations in the rise time, intermittency, and slope of toxicant pulses were quantified, whereas average concentration of the peaks remained constant across locations. Deficits in the foraging ability of crayfish exposed under these dynamic conditions paralleled the differences quantified in parameters of the turbulent toxicant plume. Given these results, the concept of toxicant exposure needs revision and needs to incorporate the more temporally based measures of toxicant dispersion. In addition, static and pulsed exposure models do not duplicate natural exposure and may not reflect behavioral or physiological impairments that occur under more realistic exposure conditions.

Modulatory effect of the exudates released by the brown kelp Lessonia spicata on the toxicity of copper in early developmental stages of ecologically related organisms

Lessonia spicata is a key dominant species along the Pacific coast of South America, providing a habitat for many organisms. However, this role can be affected by abiotic stress, such as metals. To counteract the toxic effect, L. spicata, among other seaweeds, releases exudates that bind metals. In this study, tolerances to copper of organisms related to the kelp forest (spores of Ulva lactuca (Chlorophyceae) and L. spicata (Phaeophyceae) and Zoea I of Taliepus dentatus (Milne-Edwards, Crustacea)) were studied; then, exudates are assessed by their protective effect. Exudates increase the 48-h 50% effective concentration (EC50) of the germination of spores from 8 to 23 μg Cu L-1 for U. lactuca and from 119 to 213 μg Cu L-1 for L. spicata and the survival of the larvae Zoea I 48-h 50% of lethal concentration (LC50) from 144 to 249 μg Cu L-1. Results indicated that exudates had a protective effect. Each species is specifically sensitive to copper. Crab larvae Zoea I were able to support higher doses, and exposure before hatching increased their tolerance.