Adult Amphipods Research Articles

Utilization of a Gender-Based Sorting Machine for Crustacean Selection in Bioconcentration Studies with the Freshwater Amphipod Hyalella azteca.

Bioconcentration factors (BCFs) are determined by fish flow-through tests performed according to Organisation for Economic Co-operation and Development test guideline 305. These are time-consuming and expensive and use a large number of animals. An alternative test design using the freshwater amphipod Hyalella azteca for bioconcentration studies has been recently developed and demonstrated a high potential. For bioconcentration studies using H. azteca, male amphipods are preferred compared with female organisms. Manual sexing of male adult amphipods is, however, time-consuming and requires care and skill. A new fully automatic sorting and dispensing machine for H. azteca based on image analysis has recently been developed by the company Life Science Methods. Nevertheless, an anesthesia step is necessary prior to the automatic selection. In the present study, we show that a single-pulse of 90 min of tricaine at the concentration of 1 g/L can be used and is recommended to select H. azteca males manually or automatically using the sorting machine. In the second part, we demonstrate that the machine has the ability to select, sort, and disperse the males of a culture batch of H. azteca as efficiently as manual procedures. In the last part of the study, BCFs of two organic substances were evaluated using the H. azteca bioconcentration test (HYBIT) protocol, with an anesthetizing step and robotic selection compared with manual selection without an anesthetizing step. The different BCF values obtained were in accordance with those indicated in the literature and showed that an anesthetizing step had no effect on the BCF values. Therefore, these data validated the interest in this sorting machine for selecting males to perform bioconcentrations studies with H. azteca. Environ Toxicol Chem 2023;00:1-10. © 2023 SETAC.

Amphipod Isotope Composition, Condition and Reproduction in Contrasting Sediments: A Reciprocal Transfer Experiment

Eutrophication is a process that results in excessive phytoplankton blooms, which sink to the sediment and enrich the organic matter (OM). This alters the available resources to benthic organisms and may have consequences for feeding ecology and reproduction strategies of marine populations. While effects of eutrophication on biodiversity are well documented, the more subtle effects of OM on population dynamics and diet plasticity are understudied. We performed a reciprocal transfer experiment with the benthic bioindicator amphipod Monoporeia affinis from two stations in the Baltic Sea with differing sediment OM (low and high) creating four treatments (low control, low transferred, high transferred, and high control). We investigated sediment OM effects on: i) the dietary niche and organism body condition of two different life stages of M. affinis utilizing bulk stable isotopes δ13C and δ15N, and C:N ratio; and ii) M. affinis fecundity and embryo viability. There was no initial significant differences between the females from different stations in terms of δ13C, δ15N, C:N, fecundity or viable embryos. However, we found that moving females from high OM to low OM (where the low OM sediment has higher δ15N and lower δ13C) significantly depleted their 13C values, while amphipods in low OM sediment had always significantly enriched 15N regardless of female origin indicating feeding on the new sediment. Although end-of-experiment females had lower C:N than initial females, individuals in low OM sediment presented significantly higher C:N (indicating higher body condition) than those in high OM sediment. Conversely to adult amphipods, no effects of OM were seen for juveniles δ13C or δ15N, but their individual biomass was larger in high OM sediment treatments and high OM transferred to low OM sediment. Our results indicate that the low range of sediment OM tested here altered female amphipod δ13C, δ15N and C:N ratios, with those in low OM treatments having a better body condition, but those in high OM treatments had a greater reproductive success in terms of offspring biomass. Our findings suggest a tradeoff between female condition and reproduction and indicates that even relatively small levels of sediment organic enrichment will impact female condition. Our study provides valuable information useful to interpret the effects of OM on amphipod populations used as bioindicators for anthropogenic impacts.

Ecology of ontogenetic body-mass scaling of gill surface area in a freshwater crustacean

Several studies have documented ecological effects on intraspecific and interspecific body-size scaling of metabolic rate. However, little is known about how various ecological factors may affect the scaling of respiratory structures supporting oxygen uptake for metabolism. To our knowledge, our study is the first to provide evidence for ecological effects on the scaling of a respiratory structure among conspecific populations of any animal. We compared the body-mass scaling of gill surface area (SA) among eight spring-dwelling populations of the amphipod crustacean Gammarus minus Although gill SA scaling was not related to water temperature, conductivity or G. minus population density, it was significantly related to predation regime (and secondarily to pH). Body-mass scaling slopes for gill SA were significantly lower in four populations inhabiting springs with fish predators than for four populations in springs without fish (based on comparing means of the population slopes, or slopes calculated from pooled raw data for each comparison group). As a result, gill SA was proportionately smaller in adult amphipods from springs with versus without fish. This scaling difference paralleled similar differences in the scaling exponents for the rates of growth and resting metabolic rate. We hypothesized that gill SA scaling is shallower in fish-containing versus fishless spring populations of G. minus because of effects of size-selective predation on size-specific growth and activity that in turn affect the scaling of oxygen demand and concomitantly the gill capacity (SA) for oxygen uptake. Although influential theory claims that metabolic scaling is constrained by internal body design, our study builds on previous work to show that the scaling of both metabolism and the respiratory structures supporting it may be ecologically sensitive and evolutionarily malleable.

Non-indigenous amphipods and mysids in coastal food webs of eastern Baltic Sea estuaries

The study analyses the role of non-indigenous invertebrates in the food webs of two eutrophic brackish estuarine ecosystems of the Baltic Sea: the Neva River estuary and the Curonian Lagoon, with the aim of clarifying several questions such as what trophic levels were occupied by newly established species (mainly amphipods and mysids) and whether they can affect the native benthic invertebrates as a result of their possible carnivorous nature. Stable isotope analysis (δ15N values) and gut contents analysis of field-collected specimens were used to estimate trophic level and trophic links of the newly established malacostracan crustaceans, while their consumption rates when feeding as carnivores were measured experimentally. The δ15N analysis allocated four trophic levels (TL) in the coastal food webs of both studied ecosystems with the lowest δ15N (2–4‰) for detritus and algae and the highest for fish (12–14‰). Through their high abundance, non-indigenous crustaceans (Pontogammarus robustoides, Gmelinoides fasciatus, Obessogammarus crassus, Gammarus tigrinus, Limnomysis benedeni and Paramysis lacustris) have become important members of food chains of the studied ecosystems. Their trophic position varied significantly within species during ontogenesis. This suggests that they turned from being typically detritivores/plantivorous (TL 2–2.4) at juvenile stages to omnivores (2.5–3) or to carnivores (>3) as adults. Assessment of the predation pressure by the adult amphipods on other coexisting invertebrates (in the example of the Neva Estuary) showed a low or medium impact, depending on species of predator and productivity of its potential prey organisms.

Behavioural alterations from exposure to Cu, phenanthrene, and Cu-phenanthrene mixtures: linking behaviour to acute toxic mechanisms in the aquatic amphipod, Hyalella azteca

Phenanthrene (PHE) and Cu are two contaminants commonly co-occurring in marine and freshwater environments. Mixtures of PHE and Cu have been reported to induce more-than-additive lethality in the amphipod, Hyalella azteca, a keystone aquatic invertebrate, yet little is understood regarding the interactive toxic mechanisms that mediate more-than-additive toxicity. Understanding the interactions among toxic mechanisms among Cu and PHE will allow for better predictive power in assessing the ecological risks of Cu-PHE mixtures in aquatic environments. Here we use behavioural impairment to help understand the toxic mechanisms of Cu, PHE, and Cu-PHE mixture toxicity in the aquatic amphipod crustacean, Hyalella azteca. Our principal objective was to link alterations in activity and ventilation with respiratory rates, oxidative stress, and neurotoxicity in adult H. azteca. Adult amphipods were used for all toxicity tests. Amphipods were tested at sublethal exposures of 91.8- and 195-μgL−1 Cu and PHE, respectively, and a Cu-PHE mixture at the same concentrations for 24h. Neurotoxicity was measured as acetylcholinesterase (AChE) activity, where malathion was used as a positive control. Oxidative stress was measured as reactive oxygen species (ROS) production. Phenanthrene-exposed amphipods exhibited severe behavioural impairment, being hyperstimulated to the extent that they were incapable of coordinating muscle movements. In addition, respiration and AChE activity in PHE-exposed amphipods were increased and reduced by 51% and 23% respectively. However, ROS did not increase following exposure to phenanthrene. In contrast, Cu had no effect on amphipod behaviour, respiration or AChE activity, but did lead to an increase in ROS. However, co-exposure to Cu antagonized the PHE-induced reduction in ventilation and negated any increase in respiration. The results suggest that PHE acts like an organophosphate pesticide (e.g., malathion) in H. azteca following 24h sublethal exposures, and that AChE inhibition is the likely mechanism by which PHE alters H. azteca behaviour. However, interactive aspects of neurotoxicity do not account for the previously observed more-than-additive mortality in H. azteca following exposure to Cu-PHE mixtures.

Exposure to bisphenol A modulates hormone concentrations in Gammarus pseudolimnaeus

Bisphenol A (BPA) is an endocrine-disrupting compound that can enter aquatic systems through landfill leachate or wastewater effluent. Although impacts of BPA on vertebrates are well documented, its effects on invertebrates are less clear. Amphipods such as Gammarus pseudolimnaeus Bousfield, 1958 are often prevalent invertebrates in freshwater ecosystems and can provide a powerful invertebrate model system to investigate the endocrine-disruptive capabilities of BPA. However, techniques to assay hormone concentrations in amphipods, especially vertebrate-like steroid sex hormones, are not widespread. In this study, we (i) quantified estrogen concentrations in juveniles and in adult female amphipods; (ii) quantified testosterone concentrations in juveniles and in adult male amphipods; and (iii) delineated changes to estrogen and testosterone concentrations of adults and juveniles following a 9-day exposure to BPA at four levels: 0 (control), 10, 50, and 100 µg/L BPA. Tissue extracts from homogenized samples were analyzed for estrogen or testosterone concentrations via radioimmunoassay for each reproductive class of amphipod. Low concentrations of BPA significantly increased estrogen concentrations in adult females and in juveniles. Moderate and high concentrations of BPA significantly increased testosterone concentrations in adult males, and low and moderate concentrations of BPA significantly increased testosterone concentrations of juveniles.

Analysis of feeding behavior and food consumption rate of Atlantorchestoidea brasiliensis (Crustacea: Talitridae)

Talitrid amphipods are considered one of the most important wrack-deposit consumers in the intertidal zone of sandy beaches due to their ability to remove extensive amounts of macrophytes. The quantity and composition of drift macrophytes can influence the consumption and demographic rates of talitrid species. However, on coasts with a low contribution of macrophytes, where organic material is typically composed of debris, algal fragments, and vascular plants, the feeding behavior of talitrids is poorly understood. Along the south coast of Brazil, the amphipod Atlantorchestoidea brasiliensis is the most abundant species of macrofauna on exposed sandy beaches that do not have a high abundance of macroalgal wrack. In order to understand the feeding behavior of this species, experiments on food preference and consumption rates were carried out, and the ability to feed on the surface or buried within the substrate was also tested. Food items offered included the sand crab Emerita brasiliensis, the wedge clam Donax hanleyanus, the mullet fish Mugil sp., and the alga Ulva sp., species that commonly comprise debris on the drift line. Adult amphipods showed a broad feeding range. The most commonly consumed food items were E. brasiliensis and D. hanleyanus, which were consumed more during the night, while Mugil sp. was the least consumed item during both the day and night. In the food preference trials, algal consumption was negligible, suggesting that feeding on debris is more important for this species. Amphipods preferred fresh algae rather than dried algae when simultaneously offered both food items. Our results indicate that talitrids have different feeding strategies and behavior according to the type of organic material deposited on the beach.

Sandhopper Talitrus saltator (Montagu) as a Bioindicator of Contamination by Polycyclic Aromatic Hydrocarbons

This study evaluates the use of the sandhopper Talitrus saltator as a bioindicator of PAHs contamination of the supralittoral zone of sandy beaches. Adult amphipods were collected at eight localities on the Tuscany shore in summer. Concentrations of 16 PAHs indicated as priority pollutants by the Environmental Protection Agency were determined. T. saltator is able to accumulate PAHs (total PAHs ranging from 0.75 to 62.1 ng g(-1)), with concentrations generally greater than in the sand (total PAHs ranging from 0.04 to 38 ng g(-1)). In particular, it accumulates Phe, Cry, and BbF. Preliminary laboratory tests indicate food as a possible route of PAHs intake by sandhoppers. Despite the need of further studies to clarify the variability of the PAH concentrations found in the substrata and in sandhoppers, T. saltator could be used as a bioindicator of PAHs contamination of the supralittoral zone of sandy shores.

Foraging, feeding, and reproduction on silica substrate: Increased waterborne zinc toxicity to the estuarine epibenthic amphipod Melita plumulosa

Artificial substrates consisting of fine milled silica with or without α-cellulose were evaluated for their capacity to support survival, growth, and fecundity in the amphipod Melita plumulosa. There were no significant differences in the survival and fecundity of adult amphipods maintained for up to 13 d on natural sediment, silica-only, or silica/α-cellulose substrate when fed two algal foods, Sera micron and Rotiselco-ALG. However, growth among juveniles maintained on the silica/α-cellulose mixture was significantly inhibited over 14 d compared with natural sediment. Addition of a microencapsulated shrimp feed, Frippak, to the algal foods improved juvenile growth over 28 d but still did not match the nutritive value of natural sediment. Fine silica without cellulose was subsequently used in acute and reproductive toxicity tests with waterborne zinc. With food, a 10-d median lethal concentration (LC50) of 140 µg Zn/L and a 10-d no-effect concentration (NEC) of 80 µg Zn/L were obtained for juvenile survival on silica. In contrast, a 10-d LC50 of 200 µg Zn/L and a 10-d NEC of 180 µg Zn/L were obtained for juveniles in water-only exposures. Similarly, exposure of adult females to Zn without food on silica compared with water-only exposures gave 10-d LC50s of 380 and 490 µg Zn/L and 10-d NECs of 130 and 370 µg Zn/L, respectively. The reproduction toxicity test indicated significant adult mortality at 92 µg Zn/L and significantly reduced fecundity at 22 µg Zn/L. We surmised that the toxicity of waterborne zinc to M. plumulosa increased when maintained on nutrient-depleted silica compared with water-only exposure because of increased energy expended through foraging, in concert with the likely increased exposure to Zn via the digestive tract and the gills.

Avoidance of Filial Cannibalism in the AmphipodGammarus pulex

AbstractAdult animals that cannibalise juvenile conspecifics may gain energy but also risk filial cannibalism, that is, consumption of their own offspring. However, individuals vary in the magnitude of the costs and benefits of cannibalism depending on factors such as their current energy reserves or the probability that they have offspring in the vicinity. They may therefore also vary in the extent to which they participate in cannibalism. This study investigated whether the sex or brooding status of adult amphipods (Gammarus pulex) influenced whether they participated in cannibalism of juveniles. For females carrying embryos within their brood pouch, we also investigated two hypotheses to explain the presence or absence of cannibalistic behaviour by determining whether cannibalism was correlated with factors that might reflect energy demands (body length, brood size), or that might reflect a temporal change in cannibalistic behaviour (corresponding to stage of brood development). All reproductive classes of adults participated in some level of juvenile cannibalism, but females carrying offspring at an advanced stage of development (close to emergence from the brood pouch) consumed significantly fewer juveniles than other groups. Females thus appear to significantly reduce cannibalism of juveniles concurrent with the time when their own eggs are hatching within the brood pouch, prior to the release of their offspring. Because the experiment tested female responses to unfamiliar juveniles, this reflects a temporal change in behaviour rather than a response to phenotypic recognition cues, although additional direct recognition cannot be ruled out. Brooding females with large brood sizes or large body lengths, which might have disproportionately greater energetic demands, were not more likely to cannibalise juveniles. We also noted that juveniles that survived in trials where cannibalism occurred were significantly more likely to be found at the water surface, suggesting a possible adaptation to escape cannibalistic adults. Overall, our results provide evidence that amphipods use indirect temporal cues to avoid filial cannibalism.

Incorporation of 28-d Leptocheirus plumulosus toxicity data in a sediment weight-of-evidence framework

A series of side-by-side trials were conducted to evaluate the variability of 28-d Leptocheirus plumulosus amphipod toxicity test data using existing and modified test protocols. One modification included examination of the influence of press-sieving on the sediment chemistry and the toxicity data. Press-sieving sediment did not reduce the variability in the toxicity data and also contributed uncertainty to the chemistry data. The second modification involved determining the sex of surviving adult amphipods so that the reproduction data could be measured as offspring/surviving female instead of only as offspring/surviving amphipod. Normalizing reproductive output to the number of adult females was ineffective in reducing the variability. The data from sediment toxicity tests are often interpreted in the context of 20% reductions and/or statistically significant reductions relative to negative controls. High inter-replicate variability makes default application of these decision criteria to the 28-d L. plumulosus toxicity test inappropriate regardless of whether or not samples are press-sieved or the sex of surviving amphipods is determined. This is not to say that the 28-d L. plumulosus toxicity test has no value for a sediment WOE: it provides long-term chronic data that may not otherwise be available. However, test-specific decision criteria must be established as part of the problem formulation based on the overall management goal, the availability of other lines of evidence (other toxicity tests as well as other types of data) and the desired level of certainty with respect to decision-making.

Restricted host use by the herbivorous amphipod Peramphithoe tea is motivated by food quality and abiotic refuge

There is a growing list of marine inverte- brate herbivores known to restrict their host choices to a subset of available species, yet the relative impor- tance of the evolutionary forces that select for special- ized feeding habits remain unclear. One such specialist is the gammaridean amphipod Peramphithoe tea (F. Ampithoidae) that restricts its distribution to the brown laminarian seaweed Egregia menziesii in Ore- gon. A Weld survey indicated that among available sea- weeds in the low intertidal zone of Boiler Bay, Oregon, Egregia housed greater than 90% of P. tea individuals. A set of laboratory-based habitat and feeding choice assays revealed that this specialized host distribution is likely the consequence of choices made by adult P. tea. The restricted host choice is apparently maintained by at least two evolutionary forces. First, a juvenile per- formance assay indicates that both Egregia and the co- occurring seaweed Alaria marginata, provide high food quality relative to other seaweeds available in the low- intertidal zone. Second, a Weld transplantation experi- ment revealed that Egregia protects adult amphipods from becoming dislodged with wave energy more read- ily than did Alaria. Thus, Egregia's value as good qual- ity food and refuge from abiotic stress together explain the restricted host use of P. tea. A comparison with previous studies suggests that use of Egregia is not con- sistent across the geographic range of P. tea, suggesting the possibility that the host preferences of local popu- lations may respond evolutionarily to geographic shifts in seaweed communities.

Chronic exposure of Leptocheirus plumulosus to Baltimore Harbor sediment: Bioenergetic and population-level effects

We investigated the long-term effects of contaminants in sediment from Baltimore Harbor, MD, USA, on a burrowing amphipod (Leptocheirus plumulosus) via a full life-cycle laboratory exposure. Contaminants in the Baltimore Harbor sediment included PAHs (10,800 ng/g), PCBs (152 ng/g), and heavy metals (including As, Cd, Cu, Pb, Hg, Ni, and Zn). Exposures were initiated with neonate amphipods, placed in microcosms containing either contaminated or reference sediment, and were maintained for 42 days, allowing ample time for the initial cohort to mature and reproduce. At the end of the exposure period, the populations of amphipods were surveyed to ascertain the number and size of amphipods in each size class (neonate, juvenile, and adult), and bioenergetic measurements were performed on adults, including metabolic rate, lipid content, and fecundity. Contaminated sediment from Baltimore Harbor caused lower growth and reproductive rates; in Baltimore Harbor sediment, the average dry weight of amphipod offspring in each size class was significantly lower and there were less than one-third as many individuals in each size class, compared to reference sediment. By the end of the exposure, the total amphipod biomass in Baltimore Harbor sediment was less than one quarter of that in reference sediment. On average, gravid females in reference sediment produced at least twice as many viable offspring as those in contaminated sediment. Adult male amphipods in Baltimore Harbor sediment possessed significantly lower lipid concentrations. Lipid content in neonates also appeared to be negatively affected by parental exposure to contaminants. Metabolic rate was elevated in adult amphipods exposed to Baltimore Harbor sediment. Overall, the results suggest that contaminated sediment conditions in the urban estuary may chronically affect L. plumulosus by diverting energy from production to maintenance pathways, resulting in slower growth and reduced fecundity, and ultimately leading to retarded population growth rates. The results of this study reinforce the need for long-term toxicological exposures to reveal chronic effects.

Acute toxicity and bioaccumulation of aqueous and sediment-bound metals in the estuarine amphipodMelita plumulosa

The sensitivities of juvenile and adult amphipods to metals (Cd, Cu, Ni, Pb, and Zn) in whole sediment and water-only exposures were compared using a newly developed acute test with the estuarine species Melita plumulosa. Endpoints included survival and bioaccumulation in adults, and survival and growth (body length) in juveniles over 96 h water-only and 10 day sediment exposures. Juveniles were more sensitive than adults to metals, either bound to sediments or in the aqueous phase. Although LOEC values for copper and zinc in juvenile whole-sediment tests (820 and 2290 mg/kg dry weight, respectively) were high in comparison with interim sediment quality guideline values for individual metals (270 and 410 for copper and zinc respectively), they were generally within the range of concentrations found in contaminated sediments in local estuaries. Accumulation of metals, together with the low porewater metal concentrations in whole-sediment tests, indicated that the ingestion of sediment is an important source of zinc and copper and cause of toxicity in this species.

Sensitivities of Australian and New Zealand amphipods to copper and zinc in waters and metal-spiked sediments

The sensitivities of eight benthic amphipods, Chaetocorophium cf. lucasi, Corophium colo, Grandidierella japonica, Hyale crassicornis, Hyale longicornis, Melita awa, Melita matilda and Melita plumulosa, to copper and zinc in water-only and whole-sediment toxicity tests were compared. Whole-sediment tests used copper- (1300 mg/kg) and zinc- (4000 mg/kg) spiked sediments after equilibration for sufficient time to produce pore water and overlying water concentrations below the lowest observable effect concentrations of water-only exposures. Survival of adults (after 10 d) and juveniles (after 96 h), and the metal concentrations in the body tissues of adults, were determined at the end of the tests. Two epibenthic amphipods from the genus Melita were the most sensitive species to aqueous copper and zinc, with a 96-h LC50 value of 120 μg Cu/l for both M. awa and M. plumulosa juveniles, and a 96-h LC50 value of 640 μg Zn/l for juveniles of M. plumulosa. Juvenile amphipods (7-d old) were more sensitive than adult amphipods (>30-d old) in both water-only and whole-sediment tests, with adult-LC50/juvenile-LC50 ratios in water-only tests ranging from 1.2 to l.5 for copper and 1 to 1.4 for zinc. All species except C. colo, C. cf. lucasi and M. matilda were sensitive to the copper-spiked sediment, with survival between 14% and 74% of controls. Similarly, all species except C. colo and G. japonica, showed a response to the zinc-spiked sediment (26–81% of control survival). The epibenthic amphipods were more sensitive than the infaunal tube-dwelling amphipods and are recommended as test species.

Food Partitioning between the Amphipods E chinogammarus ischnus, Gammarus fasciatus, and Hyalella azteca as Revealed by Stable Isotopes

Colonies of introduced Dreissena mussels provide substrate and food resources for benthic invertebrates resulting in increases in population abundance of many species including the native amphipod Gammarus fasciatus. Conversely, abundance of Gammarus is inversely associated with that of an introduced amphipod species, Echinogammarus ischnus. In this study, we explored carbon and nitrogen isotopic composition of E. ischnus, G. fasciatus, and Hyalella azteca and of Dreissena faeces/pseudofaeces from western Lake Erie to investigate possible exploitative competition among amphipods. Carbon isotopic composition (δ 13C) of H. azteca and G. fasciatus were similar, indicating that they share food resources, whereas E. ischnus was significantly depleted indicating its use of different resources. Dreissena faeces/pseudofaeces may be a part of G. fasciatus diet as revealed by carbon isotopic signatures, explaining, in part, why its abundance is positively associated with Dreissena. Phytoplankton may be the primary food source for juvenile E. ischnus and G. fasciatus as they had lighter carbon isotopic signatures than adult amphipods, suggesting an ontogenetic diet shift by both species. Isotopic separation of G. fasciatus and E. ischnus suggests that the latter is replacing the former by a mechanism other than exploitative competition for food.

Survival during adverse seasons reveals size‐dependent competitive ability in a deposit‐feeding amphipod, Monoporeia affinis

Previous food competition experiments indicated that small Monoporeia affinis (Lindström) amphipods are competitively superior to large conspecifics. If this is the case, large individuals such as adults should be more sensitive than their smaller conspecifics to food shortage during winter. Thus, our hypothesis was that the competitive relationships should be reflected in the winter survival between the different age‐ (size‐) classes. We investigated the effects of starvation on the survival and loss of mass of three age‐ (size‐) classes: juveniles (0+, young‐of‐the‐year) and (1+, one‐year‐old), and adults (2+, two‐year‐old) amphipods in a 10‐week experiment during the winter season. During the starvation period, the survival of the 0+ and 1+ age‐classes decreased gradually with no marked variation between the age‐classes over time, while that of the 2+ age‐class decreased dramatically after 4 weeks. The survival and swimming activity of adult (2+) amphipods were significantly lower than in the 0+ and 1+ age‐classes. The individual dry mass (W) of amphipods decreased with a rate equal to −0.0062W0.95 per day throughout the experiment, with no differences between age‐classes in the allometric scaling of the energetic costs. We found no dramatic decrease in the individual dry mass of 2+ age‐class similar to that in their survival. Using the survival results from our study to rank the age‐classes in terms of competitive ability gave the same rank order as from an earlier competition experiment. These results suggest that a starvation survival experiment prior to adverse seasons could be used to assess the competitive relationships within and between species exploiting the same resource.

The sun compass of the sandhopper Talitrus saltator: the speed of the chronometric mechanism depends on the hours of light.

Experiments on solar orientation were conducted with adult amphipods (Talitrus saltator) subjected to a reduction and/or phase shift of the hours of light (L) or dark (D) with respect to the natural photoperiod: 15 h:9 h L:D (controls), 15 h:9 h inverted (i.e. phase-shifted by 12 h and tested with the sun during the subjective night), 4 h:20 h, 20 h:4 h inverted. The sandhoppers were released in a confined environment, and individual orientation angles were recorded. The results confirm the continuous operation, through the entire 24-h period, of a chronometric mechanism of compensation for apparent solar motion. They show excellent agreement with a recently proposed model of compensation for the sun at constant (not differential) speed and they demonstrate a dependence of the speed of the chronometric mechanism on the L:D ratio in the 24-h period.

An estimation of radiation doses to benthic invertebrates from sediments collected near a Canadian uranium mine

A new method is described for calculating radiation doses to benthic invertebrates from radionuclide concentrations in freshwater sediment. Both internal and external radiation doses were estimated for all 14 principal radionuclides of the uranium-238 decay series. Sediments were collected from three sites downstream of a uranium mining operation in northern Saskatchewan, Canada. Sediments from two sites, located approximately 1.6 and 4.4 km downstream from mining operations, yielded absorbed doses to both larval midges, Chironomus tentans, and adult amphipods, Hyalella azteca, of 59–60 and 19 mGy/year, respectively, compared to 3.2 mGy/year for a nearby control site. External beta radiation from protactinium-234 ( 234Pa) and alpha radiation from uranium (U) contributed most of the dose at the impacted sites, whereas polonium-210 ( 210Po) was most important at the control site. If a weighting factor of 20 was employed for the greater biological effect of alpha vs. beta and gamma radiation, then total equivalent doses rose to 540–560 mGy/year at the site closest to uranium operations. Such equivalent doses are above the 360-mGy/year no-observed-effect level for reproductive effects in vertebrates from gamma radiation exposure. Data are not available to determine the effect of such doses on benthic organisms, but they are high enough to warrant concern. Detrimental effects have been observed in H. azteca at similar uranium concentration in laboratory toxicity tests, but it remains unclear whether the radiotoxicity or the chemotoxicity of uranium is responsible for these effects.

Runoff simulation with particle‐bound fenvalerate in multispecies stream microcosms: Importance of biological interactions

AbstractMultispecies stream microcosms were used to test the toxicity of the pyrethroid fenvalerate (FV) associated with suspended particles in order to simulate a typical runoff exposure scenario. Stream microcosms were exposed for 1 h in triplicate to 0.0, 13.6, 136, or 1,365 μg/kg FV and effects were monitored for 93 d. Experimental design allowed for detection of interspecific effects on the emergence and thus survival of the caddisfly species Limnephilus lunatus Curtis and of intraspecific effects on the spatial distribution of adult and juvenile Gammarus pulex L. (Amphipoda). Exposure at 136‐ and 1,365 μg/kg resulted in a significant acute increase in drift. Survival of L. lunatus was significantly reduced in the 1,365‐μg/kg treatment during single‐species exposures. When other species were present, survival of L. lunatus was significantly reduced at 136 μg/kg. A similar increase in test system susceptibility was observed in relation to the spatial distribution of G. pulex. Juvenile individuals avoided areas with high numbers of adult amphipods, which may prey on the juveniles. This avoidance was significant in the control and the 13.6‐μg/kg treatment but did not occur at higher levels of exposure. This study highlights the ecotoxicological importance of field‐relevant levels of particle‐associated hydrophobic chemicals that transiently increase during runoff events. Interspecific and intraspecific interactions can alter the test results; i.e., significant lethal and sublethal effects are measurable at FV levels approximately an order of magnitude lower than when biological interactions are excluded.