A multilevel approach to predict toxicity in copepod populations: assessment of growth, genetics, and population structure

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.

Passive dosing of triclosan in multigeneration tests with copepods - stable exposure concentrations and effects at the low μg/L range

Ecotoxicity testing is a crucial component of chemical risk assessment. Still, due to methodological difficulties related to controlling exposure concentrations over time, data on long-term effects of organic chemicals at low concentrations are limited. The aim of the present study was, therefore, to test the applicability of passive dosing to maintain stable concentrations of the organochlorine bacteriocide triclosan in the water phase during a 6-wk multigeneration population development test with the harpacticoid copepod Nitocra spinipes. Triclosan was loaded into silicone (1000 mg), which was used as passive dosing phase in the exposure vials. The distribution ratio for triclosan between silicone and water (D_{silicone-water} ) was 10466 ± 1927. A population development test was conducted at 3 concentration levels of triclosan that were measured to be 3 μg/L to 5 μg/L, 7 μg/L to 11 μg/L and 16 μg/L to 26 μg/L. The results demonstrate that passive dosing is applicable for long-term ecotoxicity testing of organic chemicals, including during significant growth of the test organism population. Shifts in the demographic structure of the population during exposure suggest the most severe effects were exerted on juvenile development. Progressively lower development index values in the populations exposed to increasing triclosan concentrations suggest developmental retardation. The results further stress the need for chronic exposure during ecotoxicity testing in chemical risk assessment because even the most sensitive endpoint was not significant until after 7 d of exposure. Environ Toxicol Chem 2017;36:1254-1260. © 2016 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Genetic diversity in Monoporeia affinis at polluted and reference sites of the Baltic Bothnian Bay

The amphipod Monoporeia affinis plays an important role in the Baltic Sea ecosystem as prey and as detritivore. The species is monitored for contaminant effects, but almost nothing is known about its genetics in this region. A pilot screening for genetic variation at the mitochondrial COI gene was performed in 113 individuals collected at six sites in the northern Baltic. Three coastal sites were polluted by pulp mill effluents, PAHs, and trace metals, and two coastal reference sites were without obvious connection to pollution sources. An off-coastal reference site was also included. Contaminated sites showed lower levels of genetic diversity than the coastal reference ones although the difference was not statistically significant. Divergence patterns measured as ΦST showed no significant differentiation within reference and polluted groups, but there was significant genetic divergence between them. The off-coastal sample differed significantly from all coastal sites and also showed lower genetic variation.

Acute and chronic toxicity study of the water accommodated fraction (WAF), chemically enhanced WAF (CEWAF) of crude oil and dispersant in the rock pool copepod Tigriopus japonicus

We determined the toxicity of the water accommodated hydrocarbon fraction (WAF), two chemically enhanced WAFs (CEWAFs; CEWAF-C, Crude oil+Corexit 9500 and CEWAF-H, Crude oil+Hiclean) of crude oil and two dispersants (Corexit 9500 and Hiclean) to the rock pool copepod Tigriopus japonicus. In the acute toxicity test, Corexit 9500 was the most toxic of all the chemicals studied. The nauplius stage of T. japonicus was more susceptible to the toxic chemicals studied than the adult female. The toxicity data using the nauplius stage was then considered as baseline to determine the spiking concentration of chemicals for chronic toxicity tests on the copepod. As the endpoints in the chronic toxicity test, survival, sex ratio, developmental time and fecundity of the copepod were used. All chemicals used in this study resulted in increased toxicity in the F1 generation. The lowest-observed-adverse-effect (LOAE) concentrations of WAF, CEWAF-H, CEWAF-C, Hiclean and Corexit 9500 were observed to be 50%, 10%, 0.1%, 1% and 1%, respectively. The results in present study imply that copepods in marine may be negatively influenced by spilled oil and dispersant.

Local contamination in relation to population genetic diversity and resilience of an arctic marine amphipod

The objective of this study was to investigate whether populations inhabiting a contaminated environment are affected in terms of decreased genetic diversity due to selection of tolerant genotypes and if such effect carries a cost. Marine arctic amphipod populations (Orchomenella pinguis) were collected from sites within a contaminated fjord, as well as from sites outside the fjord on the west-coast of Greenland over three years (2006-2008). Impacts on genetic diversity, effects on resilience such as development of tolerance and cost were determined. AFLP-analysis was used to explore within and between population genetic diversity, and exposure studies were performed where the populations were subjected to known and unknown stressors to assess resilience. Populations collected at three contaminated sites all had reduced genetic diversity in 2007 compared to populations outside the fjord. This pattern was different in 2008 as all contaminated site populations increased in diversity, whereas a decrease in diversity occurred at the outer sites. However, tolerance, but even more so, cost, was related to contamination exposure in 2008, in spite of the shift in genetic diversity. We suggest that contamination rapidly induces effects that can be captured as tolerance and associated cost, whereas effects on genetic diversity can be difficult to separate from recent migration events that dilute eventual decreases in diversity due to contamination pressure. As long as impacted populations can be influenced by migration events that increase the genetic diversity and add health to an affected population, populations in contaminated areas may have enhanced probability of survival.

Acute and chronic toxicity of polychlorinated biphenyl 126 to Tigriopus japonicus: effects on survival, growth, reproduction, and intrinsic rate of population growth

The harpacticoid copepod Tigriopus japonicus has a wide geographical distribution and is considered as a suitable model species for the assessment of toxicity of marine pollutants. The aim of the present study was to test the impacts of polychlorinated biphenyl (PCB) 126 (3,3',4,4',5-pentachlorobiphenyl) on the growth, development, and reproduction of T. japonicus in two successive generations. We first quantified the 96-h 50% lethal concentration (2.83 mg/L; all reported concentrations are nominal values), the no-observed-effect concentration (0.6 mg/L), and the lowest-observed-effect concentration (LOEC; 1.2 mg/L) of PCB126 in the nauplii. Nauplii were more sensitive than the adults, which still survived at the highest tested PCB126 concentration (8 mg/L). In the chronic toxicity testing, 10 life history traits were quantified for T. japonicus. No obvious effect on any of these traits was observed in the first generation (F0) at tested concentrations (<100 µg/L) lower than the LOEC. During the second generational life-cycle exposure (F1), however, PCB126 had an obvious toxic effect on the reproduction (>1 µg/L) and growth (>0.1 µg/L). Thus, copepods became more sensitive to PCB126 exposure as generations developed. Among the different traits tested, body size was the most sensitive parameter. Reproduction (fecundity, number of clutches, nauplii/clutch) and intrinsic population growth were also significantly impacted by PCB exposure. The survivorship, sex ratio, hatching time, and development were not affected. Environmental risk assessment of contaminants must therefore be based on a long-term multigenerational exposure to provide a realistic measurement of the influences of pollutants on aquatic life.

The amphipod Orchomenella pinguis--a potential bioindicator for contamination in the Arctic

Indigenous organisms can be used as bioindicators for effects of contaminants, but no such bioindicator has been established for Arctic areas. Orchomenella pinguis is a benthic amphipod, ubiquitous in the Arctic and can be found in high numbers. We collected O. pinguis at sites with different contamination levels. Population characteristics (body length distribution, average dry weight and amphipod organic content) were related to sediment contaminant concentrations, in order to identify suitable endpoints for using this species as a bioindicator. We show that O. pinguis was prevalent in both clean and contaminated areas, easy to sample and that its population characteristics could be linked to both contamination and sediment organic content. We suggest that O. pinguis is a suitable bioindicator for the Arctic, but that endpoints such as reproductive effects and phenotypic and genotypic responses are needed together with population characteristics to assess impacts of contamination.

Evidence of population genetic effects of long-term exposure to contaminated sediments-a multi-endpoint study with copepods

In the environment, pollution generally acts over long time scales and exerts exposure of multiple toxicants on the organisms living there. Recent findings show that pollution can alter the genetics of populations. However, few of these studies have focused on long-term exposure of mixtures of substances. The relatively short generation time (ca. 4-5 weeks in sediments) of the harpacticoid copepod Attheyella crassa makes it suitable for multigenerational exposure studies. Here, A. crassa copepods were exposed for 60 and 120 days to naturally contaminated sediments (i.e., Svindersviken and Trosa; each in a concentration series including 50% contaminated sediment mixed with 50% control sediment and 100% contaminated sediment), and for 120 days to control sediment spiked with copper. We assayed changes in F(ST) (fixation index), which indicates if there is any population subdivision (i.e., structure) between the samples, expected heterozygosity, percent polymorphic loci, as well as abundance. There was a significant decrease in total abundance after 60 days in both of the 100% naturally contaminated sediments. This abundance bottleneck recovered in the Trosa treatment after 120 days but not in the Svindersviken treatment. After 120 days, there were fewer males in the 100% naturally contaminated sediments compared to the control, possibly caused by smaller size of males resulting in higher surface: body volume ratio in contact with toxic chemicals. In the copper treatment there was a significant decrease in genetic diversity after 120 days, although abundance remained unchanged. Neither of the naturally contaminated sediments (50 and 100%) affected genetic diversity after 120 days but they all had high within treatment F(ST) values, with highest F(ST) in both 100% treatments. This indicates differentiation between the replicates and seems to be a consequence of multi-toxicant exposure, which likely caused selective mortality against highly sensitive genotypes. We further assayed two growth-related measures, i.e., RNA content and cephalothorax length, but none of these endpoints differed between any of the treatments and the control. In conclusion, the results of the present study support the hypothesis that toxicant exposure can reduce genetic diversity and cause population differentiation. Loss of genetic diversity is of great concern since it implies reduced adaptive potential of populations in the face of future environmental change.

The copepod Tigriopus: a promising marine model organism for ecotoxicology and environmental genomics

There is an increasing body of evidence to support the significant role of invertebrates in assessing impacts of environmental contaminants on marine ecosystems. Therefore, in recent years massive efforts have been directed to identify viable and ecologically relevant invertebrate toxicity testing models. Tigriopus, a harpacticoid copepod has a number of promising characteristics which make it a candidate worth consideration in such efforts. Tigriopus and other copepods are widely distributed and ecologically important organisms. Their position in marine food chains is very prominent, especially with regard to the transfer of energy. Copepods also play an important role in the transportation of aquatic pollutants across the food chains. In recent years there has been a phenomenal increase in the knowledge base of Tigriopus spp., particularly in the areas of their ecology, geophylogeny, genomics and their behavioural, biochemical and molecular responses following exposure to environmental stressors and chemicals. Sequences of a number of important marker genes have been studied in various Tigriopus spp., notably T. californicus and T. japonicus. These genes belong to normal biophysiological functions (e.g. electron transport system enzymes) as well as stress and toxic chemical exposure responses (heat shock protein 20, glutathione reductase, glutathione S-transferase). Recently, 40,740 expressed sequenced tags (ESTs) from T. japonicus, have been sequenced and of them, 5,673 ESTs showed significant hits (E-value, >1.0E-05) to the red flour beetle Tribolium genome database. Metals and organic pollutants such as antifouling agents, pesticides, polycyclic aromatic hydrocarbons (PAH) and polychrlorinated biphenyls (PCB) have shown reproducible biological responses when tested in Tigriopus spp. Promising results have been obtained when Tigriopus was used for assessment of risk associated with exposure to endocrine-disrupting chemicals (EDCs). Application of environmental gene expression techniques has allowed evaluation of transcriptional changes in T. japonicus with the ultimate aim of understanding the mechanisms of action of environmental stressors. Through a better understanding of toxicological mechanisms, ecotoxicologists may use this ecologically relevant species in risk assessment studies in marine systems. The combination of uses as a whole-animal bioassay and gene expression studies indicate that Tigriopus may serve as an excellent tool to evaluate the impacts of marine pollution throughout the coastal region. The purpose of this review is to illustrate the potential of using Tigriopus to fulfill the niche as an important invertebrate marine model organism for ecotoxicology and environmental genomics. In addition, the knowledge gaps and areas for further studies have also been discussed.