Cuttlefish color change as an emerging proxy for ecotoxicology.

Lately, behavioral ecotoxicology has flourished because of increasing standardization of analyses of endpoints like movement. However, research tends to focus on a few model species, which limits possibilities of extrapolating and predicting toxicological effects and adverse outcomes at the population and ecosystem level. In this regard, it is recommended to assess critical species-specific behavioral responses in taxa playing key roles in trophic food webs, such as cephalopods. These latter, known as masters of camouflage, display rapid physiological color changes to conceal themselves and adapt to their surrounding environments. The efficiency of this process depends on visual abilities and acuity, information processing, and control of chromatophores dynamics through nervous and hormonal regulation with which many contaminants can interfere. Therefore, the quantitative measurement of color change in cephalopod species could be developed as a powerful endpoint for toxicological risk assessment. Based on a wide body of research having assessed the effect of various environmental stressors (pharmaceutical residues, metals, carbon dioxide, anti-fouling agents) on the camouflage abilities of juvenile common cuttlefish, we discuss the relevance of this species as a toxicological model and address the challenge of color change quantification and standardization through a comparative review of the available measurement techniques.

In Vivo Mercury (De)Methylation Metabolism in Cephalopods under Different pCO2 Scenarios.

This work quantified the accumulation efficiencies of Hg in cuttlefish, depending on both organic (MeHg) and inorganic (Hg(II)) forms, under increased pCO2 (1600 µatm). Cuttlefish were fed with live shrimps injected with two Hg stable isotopic tracers (Me202Hg and 199Hg(II)), which allowed for the simultaneous quantification of internal Hg accumulation, Hg(II) methylation, and MeHg demethylation rates in different organs. Results showed that pCO2 had no impact on Hg bioaccumulation and organotropism, and both Hg and pCO2 did not influence the microbiota diversity of gut and digestive gland. However, the results also demonstrated that the digestive gland is a key organ for in vivo MeHg demethylation. Consequently, cuttlefish exposed to environmental levels of MeHg could exhibit in vivo MeHg demethylation. We hypothesize that in vivo MeHg demethylation could be due to biologically induced reactions or to abiotic reactions. This has important implications as to how some marine organisms may respond to future ocean change and global mercury contamination.

Bioaccumulation of inorganic and organic mercury in the cuttlefish Sepia officinalis: Influence of ocean acidification and food type.

The bioaccumulation of mercury (Hg) in marine organisms through various pathways has not yet been fully explored, particularly in cephalopods. This study utilises radiotracer techniques using the isotope 203Hg to investigate the toxicokinetics and the organotropism of waterborne inorganic Hg (iHg) and dietary inorganic and organic Hg (methylHg, MeHg) in juvenile common cuttlefish Sepia officinalis. The effect of two contrasting CO2 partial pressures in seawater (400 and 1600 µatm, equivalent to pH 8.08 and 7.54, respectively) and two types of prey (fish and shrimp) were tested as potential driving factors of Hg bioaccumulation. After 14 days of waterborne exposure, juvenile cuttlefish showed a stable concentration factor of 709 ± 54 and 893 ± 117 at pH 8.08 and 7.54, respectively. The accumulated dissolved i203Hg was depurated relatively rapidly with a radiotracer biological half-life (Tb1/2) of 44 ± 12 and 55 ± 16 days at pH 8.08 and 7.54, respectively. During the whole exposure period, approximately half of the i203Hg was found in the gills, but i203Hg also increased in the digestive gland. When fed with 203Hg-radiolabelled prey, cuttlefish assimilated almost all the Hg provided (>95%) independently of the prey type. Nevertheless, the prey type played a major role on the depuration kinetics with Hg Tb1/2 approaching infinity in fish fed cuttlefish vs. 25 days in shrimp fed cuttlefish. Such a difference is explained by the different proportion of Hg species in the prey, with fish prey containing more than 80% of MeHg vs. only 30% in shrimp. Four days after ingestion of radiolabelled food, iHg was primarily found in the digestive organs while MeHg was transferred towards the muscular tissues. No significant effect of pH/pCO2 variation was observed during both the waterborne and dietary exposures on the bioaccumulation kinetics and tissue distribution of i203Hg and Me203Hg. Dietary exposure is the predominant pathway of Hg bioaccumulation in juvenile cuttlefish.

Ecotoxicity of Heteroaggregates of Polystyrene Nanospheres in Chironomidae and Amphibian.

Due to their various properties as polymeric materials, plastics have been produced, used and ultimately discharged into the environment. Although some studies have shown their negative impacts on the marine environment, the effects of plastics on freshwater organisms are still poorly studied, while they could be widely in contact with this pollution. The current work aimed to better elucidate the impact and the toxicity mechanisms of two kinds of commercial functionalized nanoplastics, i.e., carboxylated polystyrene microspheres of, respectively, 350 and 50 nm (PS350 and PS50), and heteroaggregated PS50 with humic acid with an apparent size of 350 nm (PSHA), all used at environmental concentrations (0.1 to 100 µg L-1). For this purpose, two relevant biological and aquatic models-amphibian larvae, Xenopus laevis, and dipters, Chironomus riparius-were used under normalized exposure conditions. The acute, chronic, and genetic toxicity parameters were examined and discussed with regard to the fundamental characterization in media exposures and, especially, the aggregation state of the nanoplastics. The size of PS350 and PSHA remained similar in the Xenopus and Chironomus exposure media. Inversely, PS50 aggregated in both exposition media and finally appeared to be micrometric during the exposition tests. Interestingly, this work highlighted that PS350 has no significant effect on the tested species, while PS50 is the most prone to alter the growth of Xenopus but not of Chironomus. Finally, PSHA induced a significant genotoxicity in Xenopus.

Heteroaggregates of Polystyrene Nanospheres and Organic Matter: Preparation, Characterization and Evaluation of Their Toxicity to Algae in Environmentally Relevant Conditions.

The environmental fate and behavior of nanoplastics (NPs) and their toxicity against aquatic organisms are under current investigation. In this work, relevant physicochemical characterizations were provided to analyze the ecotoxicological risk of NPs in the aquatic compartment. For this purpose, heteroaggregates of 50 nm polystyrene nanospheres and natural organic matter were prepared and characterized. The kinetic of aggregation was assimilated to a reaction-limited colloid aggregation mode and led to the formation of heteroaggregates in the range of 100-500 nm. Toxicities of these heteroaggregates and polystyrene nanospheres (50 and 350 nm) were assessed for a large range of concentrations using four benthic and one planktonic algal species, in regards to particle states in the media. Heteroaggregates and nanospheres were shown to be stable in the exposure media during the ecotoxity tests. The algal species exhibited very low sensitivity (growth and photosynthetic activity), with the noteworthy exception of the planktonic alga, whose growth increased by more than 150% with the heteroaggregates at 1 µg L-1. Despite the lack of a strong direct effect of the NPs, they may still impair the functioning of aquatic ecosystems by destabilizing the competitive interactions between species. Moreover, further work should assess the toxicity of NPs associated with other substances (adsorbed pollutants or additives) that could enhance the NP effects.

Mercury in the tissues of five cephalopods species: First data on the nervous system.

Mercury (Hg), one of the elements most toxic to biota, accumulates within organisms throughout their lifespan and biomagnifies along trophic chain. Due to their key role in marine systems, cephalopods constitute a major vector of Hg in predators. Further, they grow rapidly and display complex behaviours, which can be altered by neurotoxic Hg. This study investigated Hg concentrations within 81 cephalopod specimens sampled in the Bay of Biscay, which belonged to five species: Eledone cirrhosa, Sepia officinalis, Loligo vulgaris, Todaropsis eblanae and Illex coindetii. Hg concentrations were measured in the digestive gland, the mantle muscle and the optic lobes of the brain. The digestive gland and the mantle were tissues with the most concentrated Hg among all species considered (up to 1.50 µg.g-1 dw), except E. cirrhosa. This benthic cephalopod had 1.3-fold higher Hg concentrations in the brain (up to 1.89 µg.g-1 dw) than in the mantle, while other species had 2-fold lower concentrations of Hg in the brain than in the mantle. Brain-Hg concentrations can be predicted from muscle-Hg concentrations for a given species, which facilitates the assessment of Hg toxicokinetics in cephalopods. In the most contaminated E. cirrhosa individual, the chemical form of Hg in its digestive gland, mantle muscle and optic lobes, was determined using High energy-Resolution X-ray Absorption Near Edge Structure (HR XANES) spectroscopy. In the digestive gland, 33 ± 11% of total Hg was inorganic Hg speciated as a dicysteinate complex (Hg(Cys)2), which suggested that the demethylation of dietary MeHg occurs in this organ. All Hg found in the mantle muscle and the optic lobes is methylated and bound to one cysteinyl group (MeHgCys complex), which implies that dietary MeHg is distributed to these tissues via the bloodstream. These results raised the questions regarding interspecific differences observed regarding Hg brain concentrations and the possible effect of Hg on cephalopod functional brain plasticity and behaviour.

Leaf mineral content govern microbial community structure in the phyllosphere of spinach (Spinacia oleracea) and rocket (Diplotaxis tenuifolia).

The plant microbiome is an important factor for plant health and productivity. While the impact of nitrogen (N) availability for plant growth and development is well established, its influence on the microbial phyllosphere community structure is unknown. We hypothesize that nitrogen impacts the growth and abundance of several microorganisms on the leaf surface. The bacterial and fungal communities of baby leaf spinach (Spinacia oleracea), and rocket (Diplotaxis tenuifolia) were investigated in a field trial for two years in a commercial setting. Nitrogen fertilizer was tested in four doses (basic nitrogen, basic + suboptimal, basic + commercial, basic + excess) with six replicates in each. Culture-independent (Illumina sequencing) and culture-dependent (viable count and identification of bacterial isolates) community studies were combined with monitoring of plant physiology and site weather conditions. This study found that alpha diversity of bacterial communities decreased in response to increasing nitrogen fertilizer dose, whereas viable counts showed no differences. Correspondingly, fungal communities of the spinach phyllosphere showed a decreasing pattern, whereas the decreasing diversity of fungal communities of rocket was not significant. Plant species and effects of annual variations on microbiome structure were observed for bacterial and fungal communities on both spinach and rocket. This study provides novel insights on the impact of nitrogen fertilizer regime on a nutrient scarce habitat, the phyllosphere.