Exposure to contaminants exacerbates oxidative stress in amphipod Monoporeia affinis subjected to fluctuating hypoxia

Temperate Versus Arctic: Unraveling the Effects of Temperature on Oil Toxicity in Gammarids

Shipping activities are increasing with sea ice receding in the Arctic, leading to higher risks of accidents and oil spills. Because Arctic toxicity data are limited, oil spill risk assessments for the Arctic are challenging to conduct. In the present study, we tested if acute oil toxicity metrics obtained at temperate conditions reflect those at Arctic conditions. The effects of temperature (4 °C, 12 °C, and 20 °C) on the median lethal concentration (LC50) and the critical body residue (CBR) of the temperate invertebrate Gammarus locusta exposed to water accommodated fractions of a fuel oil were determined. Both toxicity metrics decreased with increasing temperature. In addition, data for the temperate G. locusta were compared to data obtained for Arctic Gammarus species at 4 °C. The LC50 for the Arctic Gammarus sp. was a factor of 3 higher than that for the temperate G. locusta at 4 °C, but its CBR was similar, although both the exposure time and concentration were extended to reach lethality. Probably, this was a result of the larger size and higher weight and total lipid content of Arctic gammarids compared to the temperate gammarids. Taken together, the present data support the use of temperate acute oil toxicity data as a basis for assessing risks in the Arctic region, provided that the effects of temperature on oil fate and functional traits (e.g., body size and lipid content) of test species are considered. As such, using the CBR as a toxicity metric is beneficial because it is independent of functional traits, despite its temperature dependency. To the best of our knowledge, the present study is the first to report CBRs for oil. Environ Toxicol Chem 2024;43:1627-1637. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Multi-level toxicity assessment of polylactic acid (PLA) microplastics on the cladoceran Daphnia magna

The accumulation of plastics waste in the environment has raised a worrisome concern, moving the society to seek out for sustainable solutions, such as the transition from the use of fossil-based, conventional plastics to bioplastics (BPs). However, once in the environment bioplastics have the same probability to accumulate and experience weathering processes than conventional plastics, leading to the formation of microplastics (MPs). However, to date the information on the potential toxicity of MPs originated from the weathering of bioplastics is limited. Thus, this study aimed at investigating the adverse effects induced by the exposure to MPs made of a bioplastic polymer, the polylactic acid (PLA), towards the freshwater cladoceran Daphnia magna. Organisms were exposed for 21 days to three concentrations (0.125 µg/mL, 1.25 µg/mL and 12.5 µg/mL) of PLA microplastics (hereafter PLA-MPs). A multi-level approach was performed to investigate the potential effects through the biological hierarchy, starting from the sub-individual up to the individual level. At the sub-individual level, changes in the oxidative status (i.e., the amount of reactive oxygen species and the activity of antioxidant and detoxifying enzymes) and oxidative damage (i.e., lipid peroxidation) were explored. Moreover, the total caloric content as well as the content of protein, carbohydrate and lipid content assess were used to investigate the effects on energy reserves. At individual level the changes in swimming activity (i.e., distance moved and swimming speed) were assessed. Our results showed that the exposure to PLA-MPs induced a slight modulation in the oxidative status and energy reserves, leading to an increase in swimming behavior of treated individuals compared to control conspecifics. These results suggest that the exposure to MPs made of a bioplastic polymer can induce adverse effects similar to those caused by conventional polymers.

Does pre-exposure to polluted sediment affect sub-cellular to population-level responses to contaminant exposure in a sentinel species?

Understanding how key-species respond to anthropogenic stress such as chemical pollution is critical for predicting ecosystem changes. Little is however known about the intra-specific variability in the physiological and biochemical traits involved in contaminant exposure responses. Here, we explored this idea by exposing the Baltic amphipod Monoporeia affinis from two sites, one moderately polluted and one more pristine, to a sediment spiked with PAHs and PCBs. We evaluated the amphipods responses related to feeding, growth, a stress biomarker (acetylcholinesterase [AChE] inhibition) and stable isotope (δ13C and δ15N) composition including isotope niche analyses. More adverse responses were expected in animals from the low-pollution site than those from the high-pollution site due to tolerance development in the latter. Amphipods from both populations showed a ∼30% AChE inhibition when exposed to the contaminant spiked sediment. However, both controls and exposed amphipods from the high-pollution site had higher survival, nutrient uptake and condition status than the amphipods from the low-pollution site, which did not feed on the added diatoms as indicated by their isotope values. We found no signs of population-specific responses in physiological adjustments to contaminants with regard to classic ecotoxicological biomarkers such as AChE inhibition and growth status. Instead, isotope niche analyses proved useful in assessing contaminant stress responses at the population level.

Reduced Fitness and Elevated Oxidative Stress in the Marine Copepod Tigriopus japonicus Exposed to the Toxic Dinoflagellate Karenia mikimotoi

Blooms of the toxic dinoflagellate Karenia mikimotoi cause devastation to marine life, including declines of fitness and population recruitment. However, little is known about the effects of them on benthic copepods. Here, we assessed the acute and chronic effects of K. mikimotoi on the marine benthic copepod Tigriopus japonicus. Results showed that adult females maintained high survival (>85%) throughout 14-d incubation, but time-dependent reduction of survival was detected in the highest K. mikimotoi concentration, and nauplii and copepodites were more vulnerable compared to adults. Ingestion of K. mikimotoi depressed the grazing of copepods but significantly induced the generation of reactive oxygen species (ROS), total antioxidant capacity, activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and acetylcholinesterase. Under sublethal concentrations for two generations, K. mikimotoi reduced the fitness of copepods by prolonging development time and decreasing successful development rate, egg production, and the number of clutches. Our findings suggest that the bloom of K. mikimotoi may threaten copepod population recruitment, and its adverse effects are associated with oxidative stress.

Oxidative stress-mediated synergistic deleterious effects of nano- and microplastics in the hypoxia-conditioned marine rotifer Brachionus plicatilis

While pollution due to nano- and micro-sized plastics (NMPs) and hypoxic conditions both occur in coastal areas, the deleterious potential of co-exposure to hypoxia and NMPs (hypoxia and micro-sized plastics, HMPs; hypoxia and nano-sized plastics, HNPs) is largely unclear. Here, we provide evidence for multigenerational effects of HMP and HNP in the marine rotifer Brachionus plicatilis by investigating changes in its life traits, antioxidant system, and hypoxia-inducible factor (HIF) pathway using an orthogonal experimental design, with nanoscale and microscale particles measuring 0.05 μm and 6.0 μm in diameter, respectively, and hypoxic conditions of 0.5 mg/L for six generations. Combined exposure to NMPs and hypoxia caused a significant decrease in fecundity and overproduction of reactive oxygen species (ROS). The HIF pathway and circadian clock genes were also significantly upregulated in response to HMP and HNP exposure. In particular, synergistic deleterious effects of HNP were evident, suggesting that size-dependent toxicity can be a major driver of the effects of hypoxia and NMP co-exposure. After several generations of exposure, ROS levels returned to basal levels and transcriptomic resilience was observed, although rotifer reproduction remained suppressed. These findings help eluciating the underlying molecular mechanisms involved in responses to plastic pollution in hypoxic conditions.

Selection of formulated sediment and feeding condition for 10-day spiked-sediment toxicity test with estuarine amphipod Grandidierella japonica

This study was performed to select formulated sediment with appropriate feeding conditions for the evaluation of estuarine sediment toxicity. Grandidierella japonica, which inhabits seawater worldwide, was examined for 10-day survival, and the repeatability was evaluated under nine test conditions. The formulated sediment feeding condition combined with the highest survival rate was applied to evaluate fluoranthene toxicity in the sediment. The KB-T10 feeding condition showed the highest survival rate of 93.5%, with sufficient repeatability (4.6%). In the fluoranthene spiked-sediment toxicity test, the estimated LC50 (95% significance level) was successfully achieved under the KB-T10 condition but not under the OE-T10 condition. Therefore, we propose the use of TetraMin® (1 mg/org./day) and Kemble sediment in 10-day static spiked-sediment toxicity tests with G. japonica. Further improvements are needed for OECD sediment in seawater to increase the survival rate and prevent chemical loss due to overlying water renewal.

Effects of Diclofenac on the Reproductive Health, Respiratory Rate, Cardiac Activity, and Heat Tolerance of Aquatic Animals

Diclofenac is an important pharmaceutical present in the water cycle of wastewater treatment and one of the most distributed drugs in aquatic ecosystems. Despite the great interest in the fate of diclofenac in freshwaters, the effects of environmentally relevant concentrations on invertebrates are still unclear. Two species of freshwater invertebrates, the amphipod Gmelinoides fasciatus and the bivalve mollusk Unio pictorum, were exposed to diclofenac concentrations of 0.001-2 μg/L (environmentally relevant levels) for 96 h. A set of biological endpoints (survival, fecundity, embryo abnormalities, respiration and heart rates, heat tolerance, and cardiac stress tolerance) were estimated in exposed invertebrates. Effects of diclofenac on amphipod metabolic rate and reproduction (number and state of embryos) and adaptive capacity (cardiac stress tolerance) in both species were evident. The oxygen consumption of amphipods exposed to diclofenac of 0.1-2 μg/L was 1.5-2 times higher than in the control, indicating increased energy requirements for standard metabolism in the presence of diclofenac (>0.1 μg/L). The heart rate recovery time in mollusks after heating to critical temperature (30 °C) was 1.7 and 9 times greater in mollusks exposed to 0.1 and 0.9 μg/L, respectively, than in the control (24 min). A level of diclofenac >0.9 μg/L adversely affected amphipod embryos, leading to an increase in the number of embryos with impaired development, which subsequently died. Thus, the lowest effective concentration of diclofenac (0.1 μg/L) led to increased energy demands of animals while reducing cardiac stress tolerance, and at a level close to 1 μg/L reproductive disorders (elevated mortality of the embryos) occurred. Environ Toxicol Chem 2022;41:677-686. © 2021 SETAC.

Antioxidant Responses in Copepods Are Driven Primarily by Food Intake, Not by Toxin-Producing Cyanobacteria in the Diet

The association between oxidative processes and physiological responses has received much attention in ecotoxicity assessment. In the Baltic Sea, bloom-forming cyanobacterium Nodularia spumigena is a significant producer of various bioactive compounds, and both positive and adverse effects on grazers feeding in cyanobacteria blooms are reported. To elucidate the effect mechanisms and species sensitivity to the cyanobacteria-dominating diet, we exposed two Baltic copepods, Acartia bifilosa and Eurytemora affinis, to a diet consisting of toxin-producing cyanobacteria N. spumigena and a high-quality food Rhodomonas salina at 0–300 μg C L⁻¹; the control food was R. salina provided as a monodiet at the same food levels. The subcellular responses to food type and availability were assayed using a suite of biomarkers – antioxidant enzymes [superoxide dismutases (SOD), catalase (CAT), and glutathione S-transferases (GST)] and acetylcholinesterase (AChE). In parallel, we measured feeding activity using gut content (GC) assayed by real-time PCR analysis that quantified amounts of the prey DNA in copepod stomachs. As growth and reproduction endpoints, individual RNA content (a proxy for protein synthesis capacity), egg production rate (EPR), and egg viability (EV%) were used. In both toxic and nontoxic foods, copepod GC, RNA content, and EPR increased with food availability. Antioxidant enzyme activities increased with food availability regardless of the diet type. Moreover, CAT (both copepods), SOD, and GST (A. bifilosa) were upregulated in the copepods receiving cyanobacteria; the response was detectable when adjusted for the feeding and/or growth responses. By contrast, the diet effects were not significant when food concentration was used as a co-variable. A bimodal response in AChE was observed in A. bifilosa feeding on cyanobacteria, with up to 52% increase at the lower levels (5–25 μg C L⁻¹) and 32% inhibition at the highest food concentrations. These findings contribute to the refinement of biomarker use for assessing environmental stress and mechanistic understanding of cyanobacteria effects in grazers. They also suggest that antioxidant and AChE responses to feeding activity and diet should be accounted for when using biomarker profiles in field-collected animals in the Baltic Sea and, perhaps other systems, where toxic cyanobacteria are common.

Coupled Application of Antioxidant Defense Response and Embryo Development in Amphipod Crustaceans in the Assessment of Sediment Toxicity

Survival rate, frequency of malformed embryos, and antioxidant defense system responses in the benthic amphipod Gmelinoides fasciatus from the Baltic Sea were measured to examine the effects of toxic sediments, and to assess the usefulness of these endpoints in sediment toxicity biotesting. A highly contaminated sediment sample from the Baltic Sea was diluted with sediment from a clean site to come up with a series of 5 test sediments with dilutions from 1:32 to 1:1024, and the reference sediment. The 1:32 dilution of the test sediment was analyzed for organotins (2862 µg tin [Sn] kg dry wt ^-1 ), polycyclic aromatic hydrocarbons (6064 µg kg dry wt ^-1 ), and selected trace metals (e.g., copper 352 mg kg dry wt ^-1 ). The survival rate of G. fasciatus (10-d toxicity test) was 100% in the reference and 1:1024 treatments, and began to decline from the 1:256 dilution onward. In a 28-d experiment, various types of morphological malformations were observed in 11 to 80% of the amphipod embryos in the 1:64, 1:128, and 1:256 dilutions, with only <5% in the reference treatment. Also, elevated activities in the antioxidant defense system enzymes glutathione S-transferase and catalase were observed in amphipods exposed to the contaminated sediments compared with the reference treatment, with responses at lower contamination levels compared with the appearance of malformations in the embryos. The results obtained illustrate the effectiveness of the combined application of embryonic malformations and antioxidant defense system biomarkers in amphipods in the assessment of sediment toxicity, and potentially also of sublethal effects of chemical contamination in aquatic ecosystems. Environ Toxicol Chem 2019;38:2020-2031. © 2019 SETAC.

Insights into the morphology and molecular characterisation of glacial relict Eurytemoralacustris (Poppe, 1887) (Crustacea, Copepoda, Calanoida, Temoridae)

Eurytemoralacustris (Poppe, 1887) is a stenothermic glacial relict whose narrow environmental requirements make it an indicator species for good ecological conditions. The primary threats to this species are eutrophication and global warming. Many authors have described E.lacustris in taxonomic keys; however, its morphological description is unsatisfactory. Therefore, in this study, we aimed to review morphological characteristics of E.lacustris that were previously undescribed in the literature and to provide the molecular characteristics based on the two conservative mitochondrial genes: cytochrome c oxidase I (COI) and cytochrome b (cytb). The new record of E.lacustris indicates that it is a more widespread species than previously hypothesized. Width-to-length ratio of the last female endopod segment of legs indicates variation among the widely distributed species of the genus in Europe (i.e., E.lacustris, E.velox (Lilljeborg, 1853), and E.affinis (Poppe, 1880)). We also found variability of number of setae on the second segment of male endopod. Furthermore, our analysis confirms the occurrence of species in different than exclusively freshwater habitats.

Oxidative stress response of caddisfly Stenopsyche marmorata larvae to abrupt hypoxia-normoxia shift

Natural and anthropogenic effects cause low dissolved oxygen conditions (hypoxia) and subsequent reoxygenated conditions (normoxia) in river systems. However, oxidative stress responses to hypoxia-normoxia shift in aquatic insects are still poorly understood. Here, we exposed caddisfly Stenopsyche marmorata larvae to 30-min hypoxic followed by 1-d normoxic exposure, with experiments being repeated at 14 °C (Exp.1) and 20 °C (Exp.2), respectively. Exp.1 was conducted in December 2016 using overwintering larvae, and Exp.2 was conducted in June 2016 using non-wintering larvae. The responses of superoxide dismutase (SOD) and catalase (CAT) activity, oxygen radical absorption capacity (ORAC), lipid peroxidation (LPO), and energy reserves were investigated. The hypoxia-normoxia shift considerably inhibited CAT and ORAC in Exp.1. In addition, the energy reserves were decreased in response to exposure to severe hypoxia-normoxia. However, LPO was not induced under these conditions. It is conceivable that regulating antioxidant defense enzymes and utilizing energy reserves may suppress the expected increases in LPO. In contrast, the hypoxia-normoxia shift in Exp.2 had almost no effect on oxidative stress response, with only ORAC being induced. Exp.1 had a lower dissolved oxygen partial pressure and a larger difference in the oxygen partial pressure between hypoxia and normoxia than Exp.2. The severity of hypoxia-normoxia shift and the differences in the life cycles (overwintering or non-wintering) may cause the difference in the response of ORAC in Exp.1 and Exp.2. This study revealed that the effect of the hypoxia-normoxia shift on oxidative stress response in aquatic insects and the strength of the impact of the shift on oxidative stress response may be influenced by water temperature and life cycles.

Increase in stable isotope ratios driven by metabolic alterations in amphipods exposed to the beta-blocker propranolol

Anthropogenic pressures, such as contaminant exposure, may affect stable isotope ratios in biota. These changes are driven by alterations in the nutrient allocation and metabolic pathways induced by specific stressors. In a controlled microcosm study with the amphipod Gammarus spp., we studied effects of the β-blocker propranolol on stable isotope signatures (δ¹⁵N and δ¹³C), elemental composition (%C and %N), and growth (protein content and body size) as well as biomarkers of oxidative status (antioxidant capacity, ORAC; lipid peroxidation, TBARS) and neurological activity (acetylcholinesterase, AChE). Based on the known effects of propranolol exposure on cellular functions, i.e., its mode of action (MOA), we expected to observe a lower scope for growth, accompanied by a decrease in protein deposition, oxidative processes and AChE inhibition, with a resulting increase in the isotopic signatures. The observed responses in growth, biochemical and elemental variables supported most of these predictions. In particular, an increase in %N was observed in the propranolol exposures, whereas both protein allocation and body size declined. Moreover, both ORAC and TBARS levels decreased with increasing propranolol concentration, with the decrease being more pronounced for TBARS, which indicates the prevalence of the antioxidative processes. These changes resulted in a significant increase of the δ¹⁵N and δ¹³C values in the propranolol-exposed animals compared to the control. These findings suggest that MOA of β-blockers may be used to predict sublethal effects in non-target species, including inhibited AChE activity, improved oxidative balance, and elevated stable isotope ratios. The latter also indicates that metabolism-driven responses to environmental contaminants can alter stable isotope signatures, which should be taken into account when interpreting trophic interactions in the food webs.

Transgenerational exposure to ocean acidification induces biochemical distress in a keystone amphipod species (Gammarus locusta)

Atmospheric carbon dioxide (CO₂) levels are increasing at the fastest rate ever recorded, causing higher CO₂ dissolution in the ocean, leading to a process known as ocean acidification (OA). Unless anthropogenic CO₂ emissions are reduced, they are expected to reach ~900 ppm by the century's end, resulting in a 0.13-0.42 drop in the seawater pH levels. Since the transgenerational effects of high CO₂ in marine organisms are still poorly understood at lower levels of biological organization (namely at the biochemical level), here we reared a key ecological relevant marine amphipod, Gammarus locusta, under control and high CO₂ conditions for two generations. We measured several stress-related biochemical endpoints: i) oxidative damage [lipid peroxidation (LPO) and DNA damage]; ii) protein repair and removal mechanisms [heat shock proteins (HSPs) and ubiquitin (Ub)]; as well as iii) antioxidant responses [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione s-transferase (GST)] and total antioxidant capacity (TAC). The present results support the premise that exposure to high CO₂ is expected to decrease survival rates in this species and cause within- and transgenerational oxidative damage. More specifically, the predicted upsurge of reactive oxygen and nitrogen species seemed to overwhelm the stimulated amphipod antioxidant machinery, which proved insufficient in circumventing protein damage within the parents. Additionally, negative effects of OA are potentially being inherited by the offspring, since the oxidative stress imposed in the parent's proteome appears to be restricting DNA repair mechanisms efficiency within the offspring's. Thus, we argue that a transgenerational exposure of G. locusta could further increase vulnerability to OA and may endanger the fitness and sustainability of natural populations.

Evaluating the consumption of chemical products and articles as proxies for diffuse emissions to the environment

In this study we have evaluated the use of consumption of manufactured products (chemical products and articles) in the EU as proxies for diffuse emissions of chemicals to the environment. The content of chemical products is relatively well known. However, the content of articles (products defined by their shape rather than their composition) is less known and currently has to be estimated from chemicals that are known to occur in a small set of materials, such as plastics, that are part of the articles. Using trade and production data from Eurostat in combination with product composition data from a database on chemical content in materials (the Commodity Guide), we were able to calculate trends in the apparent consumption and in-use stocks for 768 chemicals in the EU for the period 2003-2016. The results showed that changes in the apparent consumption of these chemicals over time are smaller than in the consumption of corresponding products in which the chemicals are present. In general, our results suggest that little change in chemical consumption has occurred over the timespan studied, partly due to the financial crisis in 2008 which led to a sudden drop in the consumption, and partly due to the fact that each of the chemicals studied is present in a wide variety of products. Estimated in-use stocks of chemicals show an increasing trend over time, indicating that the mass of chemicals in articles in the EU, that could potentially be released to the environment, is increasing. The quantitative results from this study are associated with large uncertainties due to limitations of the available data. These limitations are highlighted in this study and further underline the current lack of transparency on chemicals in articles. Recommendations on how to address these limitations are also discussed.

Oxidative stress and antioxidant defense responses in Acartia copepods in relation to environmental factors

On a daily basis, planktonic organisms migrate vertically and thus experience widely varying conditions in their physico-chemical environment. In the Gulf of Finland, these changes are larger than values predicted by climate change scenarios predicted for the next century (up to 0.5 units in pH and 5°C in temperature). In this work, we are interested in how temporal variations in physico-chemical characteristics of the water column on a daily and weekly scale influence oxidative stress level and antioxidant responses in the planktonic copepod of the genus Acartia. Responses were determined from samples collected during a two-week field survey in the western Gulf of Finland, Baltic Sea. Our results showed that GST (Glutathione-S-transferase) enzyme activity increased in the surface waters between Weeks I and II, indicating antioxidant defense mechanism activation. This is most likely due to elevating temperature, pH, and dissolved oxygen observed between these two weeks. During Week II also GSSG (oxidized glutathione) was detected, indicating that copepods responded to stressor(s) in the environment. Our results suggest that Acartia copepods seem fairly tolerant to weekly fluctuations in environmental conditions in coastal and estuarine areas, in terms of antioxidant defense and oxidative stress. This could be directly connected to a very efficient glutathione cycling system acting as antioxidant defense system for neutralizing ROS and avoiding elevated levels of LPX.

Hypoxia depresses CYP1A induction and enhances DNA damage, but has minimal effects on antioxidant responses in sheepshead minnow (Cyprinodon variegatus) larvae exposed to dispersed crude oil

The growing incidence of hypoxic regions in coastal areas receiving high volumes of anthropogenic discharges requires more focused risk assessment of multiple stressors. One area needing further study is the combined effect of hypoxia and oil exposure. This study examined the short-term sublethal effects of co-exposure to hypoxia and water accommodated fractions (WAF) and chemically enhanced WAFs (CEWAFs) of Southern Louisiana Crude oil on detoxification, antioxidant defenses and genotoxicity in early life stage sheepshead minnow (Cyprinodon variegatus). CYP1A induction (evaluated by measuring EROD activity), activity of a number of key antioxidant enzymes (GST, GR, GPx, SOD, CAT, and GCL), levels of antioxidants (tGSH, GSH, and GSSG), evidence of lipid peroxidation (evaluated using the TBARS assay), and DNA damage (evaluated using the comet assay) provided a broad assessment of responses. Contaminant detoxification pathways induced by oil exposure were inhibited by co-exposure to hypoxia, indicating a maladaptive response. The interactive effects of oil and hypoxia on antioxidant defenses were mixed, but generally indicated less pronounced alterations, with significant increases in lipid peroxidation not observed. Hypoxia significantly enhanced DNA damage induced by oil exposure indicating the potential for significant deleterious effects post exposure. This study demonstrates the importance of considering hypoxia as an enhanced risk factor in assessing the effects of contaminants in areas where seasonal hypoxia may be prevalent.

Linking sub-cellular biomarkers to embryo aberrations in the benthic amphipod Monoporeia affinis

To adequately assess and monitor environmental status in the aquatic environment a broad approach is needed that integrates physical variables, chemical analyses and biological effects at different levels of the biological organization. Embryo aberrations in the Baltic Sea key species Monoporeia affinis can be induced by both metals and organic substances as well as by hypoxia, increasing temperatures and malnutrition. This amphipod has therefore been used for more than three decades as a biological effect indicator in monitoring and assessment of chemical pollution and environmental stress. However, little is known about the sub-cellular mechanisms underlying embryo aberrations. An improved mechanistic understanding may open up the possibility of including sub-cellular alterations as sensitive warning signals of stress-induced embryo aberrations. In the present study, M. affinis was exposed in microcosms to 4 different sediments from the Baltic Sea. After 88-95 days of exposure, survival and fecundity were determined as well as the frequency and type of embryo aberrations. Moreover, oxygen radical absorption capacity (ORAC) was assayed as a proxy for antioxidant defense, thiobarbituric acid reactive substances (TBARS) level as a measure of lipid peroxidation and acetylcholinesterase (AChE) activity as an indicator of neurotoxicity. The results show that AChE and ORAC can be linked to the frequency of malformed embryos and arrested embryo development. The occurrence of dead broods was significantly associated with elevated TBARS levels. It can be concluded that these sub-cellular biomarkers are indicative of effects that could affect Darwinian fitness and that oxidative stress is a likely mechanism in the development of aberrant embryos in M. affinis.

Preparation for oxidative stress under hypoxia and metabolic depression: Revisiting the proposal two decades later

Organisms that tolerate wide variations in oxygen availability, especially to hypoxia, usually face harsh environmental conditions during their lives. Such conditions include, for example, lack of food and/or water, low or high temperatures, and reduced oxygen availability. In contrast to an expected strong suppression of protein synthesis, a great number of these animals present increased levels of antioxidant defenses during oxygen deprivation. These observations have puzzled researchers for more than 20 years. Initially, two predominant ideas seemed to be irreconcilable: on one hand, hypoxia would decrease reactive oxygen species (ROS) production, while on the other the induction of antioxidant enzymes would require the overproduction of ROS. This induction of antioxidant enzymes during hypoxia was viewed as a way to prepare animals for oxidative damage that may happen ultimately during reoxygenation. The term "preparation for oxidative stress" (POS) was coined in 1998 based on such premise. However, there are many cases of increased oxidative damage in several hypoxia-tolerant organisms under hypoxia. In addition, over the years, the idea of an assured decrease in ROS formation under hypoxia was challenged. Instead, several findings indicate that the production of ROS actually increases in response to hypoxia. Recently, it became possible to provide a comprehensive explanation for the induction of antioxidant enzymes under hypoxia. The supporting evidence and the limitations of the POS idea are extensively explored in this review as we discuss results from research on estivation and situations of low oxygen stress, such as hypoxia, freezing exposure, severe dehydration, and air exposure of water-breathing animals. We propose that, under some level of oxygen deprivation, ROS are overproduced and induce changes leading to hypoxic biochemical responses. These responses would occur mainly through the activation of specific transcription factors (FoxO, Nrf2, HIF-1, NF-κB, and p53) and post translational mechanisms, both mechanisms leading to enhanced antioxidant defenses. Moreover, reactive nitrogen species are candidate modulators of ROS generation in this scenario. We conclude by drawing out the future perspectives in this field of research, and how advances in the knowledge of the mechanisms involved in the POS strategy will offer new and innovative study scenarios of biological and physiological cellular responses to environmental stress.

Sublethal exposure to azamethiphos causes neurotoxicity, altered energy allocation and high mortality during simulated live transport in American lobster

In the Bay of Fundy, New Brunswick, sea lice outbreaks in caged salmon are treated with pesticides including Salmosan(®), applied as bath treatments and then released into the surrounding seawater. The effect of chronic exposure to low concentrations of this pesticide on neighboring lobster populations is a concern. Adult male lobsters were exposed to 61 ngL(-1) of azamethiphos (a.i. in Salmosan(®) formulation) continuously for 10 days. In addition to the direct effects of pesticide exposure, effects on the ability to cope with shipping conditions and the persistence of the effects after a 24h depuration period in clean seawater were assessed. Indicators of stress and hypoxia (serum total proteins, hemocyanin and lactate), oxidative damage (protein carbonyls in gills and serum) and altered energy allocation (hepatosomatic and gonadosomatic indices, hepatopancreas lipids) were assessed in addition to neurotoxicity (chlolinesterase activity in muscle). Directly after exposure, azamethiphos-treated lobsters had inhibition of muscle cholinesterase, reduced gonadosomatic index and enhanced hepatosomatic index and hepatopancreas lipid content. All these responses persisted after 24-h depuration, increasing the risk of cumulative impacts with further exposure to chemical or non-chemical stressors. In both control and treated lobsters exposed to simulated shipment conditions, concentrations of protein and lactate in serum, and protein carbonyls in gills increased. However, mortality rate was higher in azamethiphos-treated lobsters (33 ± 14%) than in controls (2.6 ± 4%). Shipment and azamethiphos had cumulative impacts on serum proteins. Both direct effects on neurological function and energy allocation and indirect effect on ability to cope with shipping stress could have significant impacts on lobster population and/or fisheries.

Pollutant resilience in embryos of the Antarctic sea urchin Sterechinus neumayeri reflects maternal antioxidant status

Legacy pollutants, including polycyclic aromatic hydrocarbons (PAHs) and metals, can occur in high concentrations in some Antarctic marine environments, particularly near scientific research stations. Oxidative stress is an important unifying feature underlying the toxicity of many chemical contaminants to aquatic organisms. However, the potential impacts of pollutants on the oxidative physiology of Antarctic marine invertebrates are not well documented. Sterechinus neumayeri is a common animal in the shallow subtidal benthos surrounding Antarctica, and is considered an important keystone species. The aim of the present study was to collect baseline oxidative biomarker data for S. neumayeri and to investigate the impacts of field exposure to chemical contaminants on gamete health and parent-to-offspring transfer of oxidative stress resilience. We analysed antioxidant enzyme activities, levels of the molecular antioxidant glutathione, protein carbonylation, lipid peroxidation and levels of 8-OHdG as oxidative stress biomarkers in S. neumayeri from a contaminant-impacted site near McMurdo Station and a relatively pristine site at Cape Evans. Biomarkers were analysed in adult gamete tissue and in early stage embryos exposed to AN8 fuel oil. PAHs were quantified as a proxy for contamination and were found to be elevated in urchins from the contaminated site (up to 231.67ng/g DW). These contaminant-experienced adult urchins produced eggs with greater levels of a broad suite of antioxidants, particularly superoxide dismutase, catalase and glyoxalase-I, than those from Cape Evans. In addition, embryos that were derived from contaminant-experienced mothers were endowed with higher baseline levels of antioxidants, which conferred an enhanced capacity to minimize oxidative damage to lipids, proteins and DNA when exposed to AN8 fuel. This pattern was strongest following exposure to 900ppm AN8, where lipid and protein damage was 5-7 times greater than baseline levels in contaminant-naïve female embryos in comparison to 3-4 times greater in contaminant-experienced female embryos. Despite this inherited resilience against oxidative stress, abnormal development was as high in these embryos when exposed to AN8 as in those derived from contaminant-naïve mothers (up to 80% abnormality), implying the conferred advantage may not translate to a fitness or survival gain, at least up to the blastulae stage. Our findings document the first evidence for parent-to-offspring transfer of oxidative stress resilience in an Antarctic marine invertebrate.

Influence of copper pre-exposure on biochemical responses of the sea anemone Bunodosoma cangicum to changes in oxygen availability

The influence of copper on the ability of the intertidal sea anemone Bunodosoma cangicum to cope with reactive oxygen species generation associated with changes in oxygen availability was evaluated. Sea anemones were kept under control condition or pre-exposed (96 h) to dissolved copper (6.1 μg ± 2.7 μg/L) and then subjected to a 6-h period of hypoxia (0.5mg O₂/L) followed by a 6-h period of re-oxygenation (7.5mg O₂/L). Antioxidant capacity against peroxyl radicals (ACAP), superoxide dismutase (SOD) activity, reduced glutathione (GSH) concentration, lipid peroxidation (LPO) level, and ATP concentration were evaluated. Control sea anemones showed variations in SOD and LPO while copper pre-exposed sea anemones displayed changes in ACAP, GSH, LPO and ATP. However, no clear pattern of change over time was observed. ACAP was lower in copper pre-exposed sea anemones than in the control ones during hypoxia and recovery. SOD activity was increased during hypoxia and reduced shortly after recovery in control sea anemones. GSH concentration was higher in copper pre-exposed sea anemones than in the control ones in all experimental conditions. The LPO level increased shortly after recovery in both groups of sea anemones, being higher in control sea anemones than in copper pre-exposed ones. ATP concentration showed transient changes in copper pre-exposed sea anemones, being lower in these sea anemones than in control ones during recovery. These findings suggest that B. cangicum possess mechanisms to prevent oxidative stress generated by changes in oxygen availability associated with the tidal cycle, which can be disturbed by pre-exposure to copper.

Sucralose induces biochemical responses in Daphnia magna

The intense artificial sweetener sucralose has no bioconcentration properties, and no adverse acute toxic effects have been observed in standard ecotoxicity tests, suggesting negligible environmental risk. However, significant feeding and behavioural alterations have been reported in non-standard tests using aquatic crustaceans, indicating possible sublethal effects. We hypothesized that these effects are related to alterations in acetylcholinesterase (AChE) and oxidative status in the exposed animals and investigated changes in AChE and oxidative biomarkers (oxygen radical absorbing capacity, ORAC, and lipid peroxidation, TBARS) in the crustacean Daphnia magna exposed to sucralose (0.0001-5 mg L(-1)). The sucralose concentration was a significant positive predictor for ORAC, TBARS and AChE in the daphnids. Moreover, the AChE response was linked to both oxidative biomarkers, with positive and negative relationships for TBARS and ORAC, respectively. These joint responses support our hypothesis and suggest that exposure to sucralose may induce neurological and oxidative mechanisms with potentially important consequences for animal behaviour and physiology.

Biomonitoring toxicity of natural sediments using juvenile Hyalella curvispina (Amphipoda) as test species: evaluation of early effect endpoints

The utility of early effect endpoints as biomarkers of ecotoxicity of natural sediments in water-sediment static system was investigated. The particular goal was to evaluate the ecotoxicity of the sediment samples from La Choza stream, located in upper basin of the Reconquista river, the second most polluted river of Argentina. Native juveniles Hyalella curvispina were used as test organisms evaluating survival, growth, oxidative stress parameters (SOD; CAT, TBARS) and the electron transport system (ETS) activity as early toxic effect. This study used methodologies and techniques that allow the assessment of sediment pollution with a native species as test organism and provided data to discuss the viability of sublethal endpoints as tools for freshwater sediment assessment. In spring and in summer two ten-day series of whole-sediment assays were conducted simultaneously: (a) standard assays and (b) biomarkers assays. A control sediment was ran simultaneously in which no--effect on survival was measured. In summer there was a significant increase in length and biomass in both exposed and control groups. In spring an inhibitory effect on growth and an increase in oxidative damage with a concomitant rise in antioxidant defenses, was observed in animals exposed to La Choza sediment. ETS measurement indicated a significant depression of metabolic activity of amphipods exposed to contaminated sediments. The measured biomarkers represent the first record for juvenile H. curvispina exposed to polluted natural sediments under standardized laboratory conditions. The used bioanalytical tools demonstrated higher sensitivity and a more accurate assessment of the effects than those obtained by the standard tests of survival and growth. We propose their adoption in biomonitoring of freshwater sediment toxicity.

Development of tools for integrated monitoring and assessment of hazardous substances and their biological effects in the Baltic Sea

The need to develop biological effects monitoring to facilitate a reliable assessment of hazardous substances has been emphasized in the Baltic Sea Action Plan of the Helsinki Commission. An integrated chemical-biological approach is vitally important for the understanding and proper assessment of anthropogenic pressures and their effects on the Baltic Sea. Such an approach is also necessary for prudent management aiming at safeguarding the sustainable use of ecosystem goods and Services. The BEAST project (Biological Effects of Anthropogenic Chemical Stress: Tools for the Assessment of Ecosystem Health) set out to address this topic within the BONUS Programme. BEAST generated a large amount of quality-assured data on several biological effects parameters (biomarkers) in various marine species in different sub-regions of the Baltic Sea. New indicators (biological response measurement methods) and management tools (integrated indices) with regard to the integrated monitoring approach were suggested.

Projected marine climate change: effects on copepod oxidative status and reproduction

Zooplankton are an important link between primary producers and fish. Therefore, it is crucial to address their responses when predicting effects of climate change on pelagic ecosystems. For realistic community-level predictions, several biotic and abiotic climate-related variables should be examined in combination. We studied the combined effects of ocean acidification and global warming predicted for year 2100 with toxic cyanobacteria on the calanoid copepod, Acartia bifilosa. Acidification together with higher temperature reduced copepod antioxidant capacity. Higher temperature also decreased egg viability, nauplii development, and oxidative status. Exposure to cyanobacteria and its toxin had a negative effect on egg production but, a positive effect on oxidative status and egg viability, giving no net effects on viable egg production. Additionally, nauplii development was enhanced by the presence of cyanobacteria, which partially alleviated the otherwise negative effects of increased temperature and decreased pH on the copepod recruitment. The interactive effects of temperature, acidification, and cyanobacteria on copepods highlight the importance of testing combined effects of climate-related factors when predicting biological responses.

Role of redox metabolism for adaptation of aquatic animals to drastic changes in oxygen availability

Large changes in oxygen availability in aquatic environments, ranging from anoxia through to hyperoxia, can lead to corresponding wide variation in the production of reactive oxygen species (ROS) by animals with aquatic respiration. Therefore, animals living in marine, estuarine and freshwater environments have developed efficient antioxidant defenses to minimize oxidative stress and to regulate the cellular actions of ROS. Changes in oxygen levels may lead to bursts of ROS generation that can be particularly harmful. This situation is commonly experienced by aquatic animals during abrupt transitions from periods of hypoxia/anoxia back to oxygenated conditions (e.g. intertidal cycles). The strategies developed differ significantly among aquatic species and are (i) improvement of their endogenous antioxidant system under hyperoxia (that leads to increased ROS formation) or other similar ROS-related stresses, (ii) increase in antioxidant levels when displaying higher metabolic rates, (iii) presence of constitutively high levels of antioxidants, that attenuates oxidative stress derived from fluctuations in oxygen availability, or (iv) increase in the activity of antioxidant enzymes (and/or the levels of their mRNAs) during hypometabolic states associated with anoxia/hypoxia. This enhancement of the antioxidant system - coined over a decade ago as "preparation for oxidative stress" - controls the possible harmful effects of increased ROS formation during hypoxia/reoxygenation. The present article proposes a novel explanation for the biochemical and molecular mechanisms involved in this phenomenon that could be triggered by hypoxia-induced ROS formation. We also discuss the connections among oxygen sensing, oxidative damage and regulation of the endogenous antioxidant defense apparatus in animals adapted to many natural or man-made challenges of the aquatic environment.