Development of the sea urchin Heliocidaris crassispina from Hong Kong is robust to ocean acidification and copper contamination

Parentage influence on gene expression under acidification revealed through single-embryo sequencing

The dissolution of anthropogenic carbon dioxide (CO2 ) in seawater has altered its carbonate chemistry in the process of ocean acidification (OA). OA affects the viability of marine species. In particular, calcifying organisms and their early planktonic larval stages are considered vulnerable. These organisms often utilize energy reserves for metabolism rather than growth and calcification as supported by bulk RNA-sequencing (RNA-seq) experiments. Yet, transcriptomic profiling of a bulk sample reflects the average gene expression of the population, neglecting the variations between individuals, which forms the basis for natural selection. Here, we used single-embryo RNA-seq on larval sea urchin Heliocidaris crassispina, which is a commercially and ecologically valuable species in East Asia, to document gene expression changes to OA at an individual and family level. Three paternal half-sibs groups were fertilized and exposed to 3 pH conditions (ambient pH 8.0, 7.7 and 7.4) for 12 h prior to sequencing and oxygen consumption assay. The resulting transcriptomic profile of all embryos can be distinguished into four clusters, with differences in gene expressions that govern biomineralization, cell differentiation and patterning, as well as metabolism. While these responses were influenced by pH conditions, the male identities also had an effect. Specifically, a regression model and goodness of fit tests indicated a significant interaction between sire and pH on the probability of embryo membership in different clusters of gene expression. The single-embryo RNA-seq approach is promising in climate stressor research because not only does it highlight potential impacts before phenotypic changes were observed, but it also highlights variations between individuals and lineages, thus enabling a better determination of evolutionary potential.

Different ecological histories of sea urchins acclimated to reduced pH influence offspring response to multiple stressors

End-of-the-century predictions on carbon dioxide (CO₂) driven ocean acidification and the continuous leakage of pesticides from inland to coastal areas are of concern for potential negative effects on marine species' early life stages which are the most vulnerable to environmental changes. Variations in seawater chemistry related to human activities may interfere with the normal development from embryo to juvenile/adult stage. However, transgenerational studies suggest that the parental generation can influence the offspring phenotype, and thus their performances, based on the environment experienced. Here we compared the transgenerational responses to a multiple stressor scenario in sea urchins (Paracentrotus lividus) that experienced different environments since their settlement: i.e., animals from a highly variable environment, such as the Venice lagoon, versus animals from a coastal area with prevailing oligotrophic conditions in the Northern Adriatic Sea. After long-term maintenance (2 and 6 months) of adult sea urchins at natural and -0.4 units reduced pH, the F1 generations were obtained. Embryos were reared under four experimental conditions: natural and -0.4 pH both in the absence and in the presence of an emerging contaminants' mixture (glyphosate and aminomethylphosphonic acid at environmentally relevant concentrations, 100 μg/L). A significant detrimental effect of both the parental and the filial pH was highlighted, affecting embryo development and growth. Nonetheless, sea urchins from both sites were able to cope with ocean acidification. The 6-months F1 response was better than that of the 2-months F1. Conversely, the F1 response of the sea urchins maintained at natural conditions did not change sensibly after more prolonged parental exposure. An additive but mild negative effect of the mixture was observed, mostly in lagoon offspring. Results suggest that long-term exposure to reduced pH leads to transgenerational acclimation but does not affect susceptibility to the tested pollutants.

Surviving in a changing ocean. Tolerance to acidification might affect the susceptibility of polychaetes to chemical contamination

This study aimed to assess the combined effects of ocean acidification (OA) and pollution to the polychaete Syllis prolifera inhabiting the CO₂ vent system of the Castello Aragonese (Ischia Island, Italy). We investigated the basal activities of antioxidant enzymes in organisms from the acidified site and from an ambient-pH control site in two different periods of the year. Results showed a limited influence of acidified conditions on the functionality of the antioxidant system. We then investigated the responsiveness of individuals living inside the CO₂ vent compared to those from the control to face exposure to acetone and copper. Results highlighted a higher susceptibility of organisms from the vent to acetone and a different response of antioxidant enzymes in individuals from the two sites. Conversely, a higher tolerance to copper was observed in polychaetes from the acidified-site with respect to controls, but any significant oxidative stress was induced at sublethal concentrations.

Ocean Acidification, but Not Environmental Contaminants, Affects Fertilization Success and Sperm Motility in the Sea Urchin Paracentrotus lividus

Ocean acidification poses an increasing concern for broadcast spawning species that release gametes in the water column where fertilization occurs. Indeed, the functionality of gametes and their interactions may be negatively affected by reduced pH. Susceptibility to other environmental stressors, such as pollutants, may be also altered under acidified conditions, resulting in more detrimental effects. To verify this hypothesis, combined exposures to CO2-driven acidification and environmentally relevant concentrations (0.5 µg/L) of three contaminants (caffeine, diclofenac, and PFOS, all singularly or in mixture) were carried out to highlight potential negative effects on fertilization success and motility of sperm in the sea urchin Paracentrotus lividus. Our results showed a significant reduction in the percentage of fertilized eggs when sperm were pre-exposed to reduced pH (ambient pH minus 0.4 units) compared to that of controls (ambient, pH = 8.1). Sperm speed and motility also decreased when sperm were activated and then exposed at reduced pH. Conversely, at both pH values tested, no significant effect due to the contaminants, nor of their interaction with pH, was found on any of the biological endpoints considered.

Exacerbation of copper pollution toxicity from ocean acidification: A comparative analysis of two bivalve species with distinct sensitivities

In estuarine ecosystems, bivalves experience large pH fluctuations caused by the anthropogenic elevation of atmospheric CO₂ and Cu pollution. This study investigates whether Cu toxicity increases indiscriminately in two bivalve species from different estuarine habitats as a result of elevated Cu bioaccumulation in acidified seawater. This was carried out by evaluating the effects of Cu exposure on two bivalve species (clams and scallops) for 28 d, at a series of gradient pH levels (pH 8.1, 7.8, and 7.6). The results demonstrated an increase in the Cu content in the soft tissues of clams and scallops in acidified seawater. Cu toxicity increased under acidified seawater by affecting the molecular pathways, physiological function, biochemical responses, and health status of clams and scallops. An iTRAQ-based quantitative proteomic analysis showed increased protein turnover, disturbed cytoskeleton and signal transduction pathways, apoptosis, and suppressed energy metabolism pathways in the clams and scallops under joint exposure to ocean acidification and Cu. The integrated biomarker response results suggested that scallops were more sensitive to Cu toxicity and/or ocean acidification than clams. The proteomic results suggested that the increased energy metabolism and suppressed protein turnover rates may contribute to a higher resistivity to ocean acidification in clams than scallops. Overall, this study provides molecular insights into the distinct sensitivities between two bivalve species from different habitats under exposure to ocean acidification and/or Cu. The findings emphasize the aggravating impact of ocean acidification on Cu toxicity in clams and scallops. The results show that ocean acidification and copper pollution may reduce the long-term viability of clams and scallops, and lead to the degradation of estuarine ecosystems.

Near future ocean acidification modulates the physiological impact of fluoxetine at environmental concentration on larval urchins

Pharmaceuticals found in human wastes are emergent pollutants that are continuously released into aquatic systems. While exposure to pharmaceuticals alone could adversely impact aquatic organisms, few studies have considered the interactive effects of pharmaceuticals and the future environmental conditions, such as decreasing pH due to ocean acidification. Given the bioavailability of many pharmaceuticals is dependent on these physical conditions, we investigated the effect of environmentally-relevant concentrations of fluoxetine (10 and 100 ng L^-1) under ambient (pH 8.0) and reduced pH conditions (pH 7.7) on physiology, behavior, and DNA integrity of larval sea urchins (Heliocidaris crassispina). Notably, the negative impacts of fluoxetine exposure were attenuated by reduced pH. Larvae exposed to both reduced pH and fluoxetine exhibited lower levels of DNA damage compared to those exposed to only one of the stressors. Similar antagonistic interactions were observed at the organismal level: for example, fluoxetine exposure at 10 ng L^-1 under ambient pH increased the percentage of embryos at later developmental stages, but such effects of fluoxetine were absent at pH 7.7. However, despite the modulation of fluoxetine impacts under ocean acidification, control larvae performed better than those exposed to either stressor, alone or in combination. We also observed that pH alone impacted organismal behaviors, as larvae swam slower at reduced pH regardless of fluoxetine exposure. Our findings highlight the need to consider multi-stressor interactions when determining future organismal performance and that multiple metrics are needed to paint a fuller picture of ecological risks.

Acquiring an evolutionary perspective in marine ecotoxicology to tackle emerging concerns in a rapidly changing ocean

Tens of thousands of anthropogenic chemicals and wastes enter the marine environment each year as a consequence of the ever-increasing anthropogenic activities and demographic growth of the human population, which is majorly concentrated along coastal areas. Marine ecotoxicology has had a crucial role in helping shed light on the fate of chemicals in the environment, and improving our understanding of how they can affect natural ecosystems. However, chemical contamination is not occurring in isolation, but rather against a rapidly changing environmental horizon. Most environmental studies have been focusing on short-term within-generation responses of single life stages of single species to single stressors. As a consequence, one-dimensional ecotoxicology cannot enable us to appreciate the degree and magnitude of future impacts of chemicals on marine ecosystems. Current approaches that lack an evolutionary perspective within the context of ongoing and future local and global stressors will likely lead us to under or over estimations of the impacts that chemicals will exert on marine organisms. It is therefore urgent to define whether marine organisms can acclimate, i.e. adjust their phenotypes through transgenerational plasticity, or rapidly adapt, i.e. realign the population phenotypic performances to maximize fitness, to the new chemical environment within a selective horizon defined by global changes. To foster a significant advancement in this research area, we review briefly the history of ecotoxicology, synthesis our current understanding of the fate and impact of contaminants under global changes, and critically discuss the benefits and challenges of integrative approaches toward developing an evolutionary perspective in marine ecotoxicology: particularly through a multigenerational approach. The inclusion of multigenerational studies in Ecological Risk Assessment framework (ERA) would provide significant and more accurately information to help predict the risks of pollution in a rapidly changing ocean.

Combined Effects of Diatom-Derived Oxylipins on the Sea Urchin Paracentrotus lividus

Oxylipins are diatom-derived secondary metabolites, deriving from the oxidation of polyunsatured fatty acids that are released from cell membranes after cell damage or senescence of these single-celled algae. Previous results revealed harmful toxic effects of polyunsaturated aldehydes (PUAs) and hydroxyacids (HEPEs) on sea urchin Paracentrotus lividus embryonic development by testing individual compounds and mixtures of the same chemical group. Here, we investigated the combined effects of these compounds on sea urchin development at the morphological and molecular level for the first time. Our results demonstrated that oxylipin mixtures had stronger effects on sea urchin embryos compared with individual compounds, confirming that PUAs induce malformations and HEPEs cause developmental delay. This harmful effect was also confirmed by molecular analysis. Twelve new genes, involved in stress response and embryonic developmental processes, were isolated from the sea urchin P. lividus; these genes were found to be functionally interconnected with 11 genes already identified as a stress response of P. lividus embryos to single oxylipins. The expression levels of most of the analyzed genes targeted by oxylipin mixtures were involved in stress, skeletogenesis, development/differentiation, and detoxification processes. This work has important ecological implications, considering that PUAs and HEPEs represent the most abundant oxylipins in bloom-forming diatoms, opening new perspectives in understanding the molecular pathways activated by sea urchins exposed to diatom oxylipins.

Harmful effects of cocaine byproduct in the reproduction of sea urchin in different ocean acidification scenarios

This study has as main objective assessing the toxicity of crack-cocaine combined with different scenarios of ocean acidification on fertilization rate and embryo-larval development of Echinometra lucunter sea urchin. Effects on early life stages were assessed at five different concentrations (6,25 mg.L^-1; 12,5 mg.L^-1; 25 mg.L^-1; 50 mg.L^-1 and 100 mg.L^-1) of crack-cocaine at four different pH values (8.5; 8.0; 7.5; 7.0). The pH values were achieved using two different methodologies: adding hydrochloric acid (HCl) and injecting carbon dioxide (CO₂). The fertilization test did not show significant differences (p ≤ 0.05) compared with control sample at pH values 8.5; 8.0 and 7.5. Results of embryo-larval assays showed a half maximal effective concentration (EC50) of crack-cocaine at pH values tested (8.5, 8.0, 7.5) as 58.83, 10.67 and 11.58 mg/L^-1 for HCl acidification and 58.83, 23.28 and 12.57 mg/L^-1 for CO₂ enrichment. At pH 7.0 the effects observed in fertilization rate and embryo development were associated with the acidification. This study is the first ecotoxicological assessment of illicit drug toxicity in aquatic ecosystems at different ocean acidification scenarios.

Synergistic Effects of Climate Change and Marine Pollution: An Overlooked Interaction in Coastal and Estuarine Areas

Coastal areas have been increasingly affected by human activities, marine pollution and climate change are among the most important pressures affecting these environments. Human-induced pressures occur in a cumulative way and generate additive, antagonistic or synergistic effects. Knowledge on synergistic effects is crucial to coastal zone management, since they may imply a change in human uses of these systems, as well as dedicated action plans in order to reduce hazards and environmental risks. In this work, we provide an overview of the available literature on synergistic effects between climate change and chemical pollution, and discuss current knowledge, methodological approaches, and research gaps and needs. Interactions between these two pressures may be climate change dominant (climate change leads to an increase in contaminant exposure or toxicity) or contaminant-dominant (chemical exposure leads to an increase in climate change susceptibility), but the mechanistic drivers of such processes are not well known. Results from a few meta-analyses studies and reviews showed that synergistic interactions tend to be more frequent compared to additive and antagonistic ones. However, most of the studies are individual-based and assess the cumulative effects of a few contaminants individually in laboratory settings together with few climate variables, particularly temperature and pH. Nevertheless, a wide diversity of contaminants have already been individually tested, spanning from metals, persistent organic pollutants and, more recently, emergent pollutants. Population and community based approaches are less frequent but have generated very interesting and more holistic perspectives. Methodological approaches are quite diverse, from laboratory studies to mesocosm and field studies, or based on statistical or modelling tools, each with their own potential and limitations. More holistic comparisons integrating several pressures and their combinations and a multitude of habitats, taxa, life-stages, among others, are needed, as well as insights from meta-analyses and systematic reviews.

Ocean acidification buffers the physiological responses of the king ragworm Alitta virens to the common pollutant copper

Ocean acidification (OA) has the potential to alter the bioavailability of pH sensitive metals contaminating coastal sediments, particularly copper, by changing their speciation in seawater. Hence OA may drive increased toxicity of these metals to coastal biota. Here, we demonstrate complex interactions between OA and copper on the physiology and toxicity responses of the sediment dwelling polychaete Alitta virens. Worm coelomic fluid pCO₂ was not increased by exposure to OA conditions (pH_NBS 7.77, pCO₂ 530 μatm) for 14 days, suggesting either physiological or behavioural responses to control coelomic fluid pCO₂. Exposure to 0.25 μM nominal copper caused a decrease in coelomic fluid pCO₂ by 43.3% and bicarbonate ions by 44.6% but paradoxically this copper-induced effect was reduced under near-future OA conditions. Hence OA appeared to 'buffer' the copper-induced acid-base disturbance. DNA damage was significantly increased in worms exposed to copper under ambient pCO₂ conditions, rising by 11.1% compared to the worms in the no copper control, but there was no effect of OA conditions on the level of DNA damage induced by copper when exposed in combination. These interactions differ from the increased copper toxicity under OA conditions reported for several other invertebrate species. Hence this new evidence adds to the developing paradigm that species' physiology is key in determining the interactions of these two stressors rather than it purely being driven by the changes in metal chemistry under lower seawater pH.

Assessment of individual and mixed toxicity of bromoform, tribromoacetic-acid and 2,4,6 tribromophenol, on the embryo-larval development of Paracentrotus lividus sea urchin

Water chlorination is the most widely used technique to avoid microbial contamination and biofouling. Adding chlorine to bromide-rich waters leads to the rapid oxidation of bromide ions and leads to the formation of brominated disinfection by-products (bromo-DBPs) that exert adverse effects on various biological models. Bromo-DBPs are regularly encountered within industrialized embayments, potentially impacting marine organisms. Of these, bromoform, tribromoacetic acid and tribromophenol are among the most prevalent. In the present study, we tested the potential toxicity and genotoxicity of these disinfection by-products, using sea urchin, Paracentrotus lividus, embryos. We highlighted that tribromophenol showed higher toxicity compared to bromoform and tribromoacetic acid. Furthermore, a synergistic effect was detected when tested in combination. Pluteus cells exposed for 1 h to mixtures of DBPs at several concentrations demonstrated significant DNA damage. Finally, when compared to a non-exposed population, sea urchins living in a bromo-DPB-polluted area produced more resistant progenies, as if they were locally adapted. This hypothesis remains to be tested in order to better understand the obvious impact of complex bromo-DBPs environments on marine wildlife.

Seawater acidification increases copper toxicity: A multi-biomarker approach with a key marine invertebrate, the Pacific Oyster Crassostrea gigas

Ocean acidification (OA) has been found to increase the release of free Cu²⁺ in seawater. However, only a handful of studies have investigated the influence of OA on Cu accumulation and cellular toxicity in bivalve species. In this study, Pacific oysters, Crassostrea gigas, were exposed to 25 μg/L Cu²⁺ at three pH levels (8.1, 7.8 and 7.6) for 14 and 28 days. Physiological and histopathological parameters [(clearance rate (CR), respiration rate (RR), histopathological damage and condition index (CI)), oxidative stress and neurotoxicity biomarkers [superoxide dismutase (SOD) and glutathione transferase (GST) activities, lipid peroxidation (LPO) and acetylcholinesterase (AChE) activity], combined with glycolytic enzyme activities [pyruvate kinase (PK) and hexokinase (HK)] were investigated in C. gigas. The bioconcentration of Cu was increased in soft tissues of Cu-exposed oysters under OA. Our results suggest that both OA and Cu could lead to physiological disturbance, oxidative stress, cellular damage, disturbance in energy metabolism and neurotoxicity in oysters. The inhibited CR, increased glycolytic enzymes activities and decreased CI suggested that the energy metabolism strategy adopted by oysters was not sustainable in the long term. Furthermore, integrated biomarker response (IBR) results found that OA and Cu exposure lead to severe stress to oysters, and co-exposure was the most stressful condition. Results from this study highlight the need to include OA in future environmental assessments of pollutants and hazardous materials to better elucidate the risks of those environmental perturbations.