Integrated behavioural and physiological responses of sand smelt larvae to the effects of warming and hypoxia as combined stressors.

Forecasts indicate that rising temperatures towards the future and the expansion of dead zones will change environmental suitability for fish early stages. Therefore, we assessed the chronic effects of warming (26 °C), hypoxia (<2-2.5 mg L-1) or their combination on mortality rate, growth, behaviour, energy metabolism and oxidative stress using Atherina presbyter larvae as a model species. There were no differences between the treatments in terms of mortality rate. The combination of warming and hypoxia induced faster loss of body mass (+22.7%). Warming, hypoxia or their combination enhanced boldness (+14.7-25.4%), but decreased exploration (-95%-121%), increased the time in frozen state (+60.6-80.5%) and depleted swimming speed (-45.6-50.5%). Moreover, routine metabolic rate was depleted under hypoxia or under the combination of warming and hypoxia (-56.6 and 57.2%, respectively). Under hypoxia, increased catalase activity (+56.3%) indicates some level of antioxidant defence capacity, although increased DNA damage (+25.2%) has also been observed. Larvae also exhibited a great capacity to maintain the anaerobic metabolism stable in all situations, but the aerobic metabolism is enhanced (+19.3%) when exposed to the combination of both stressors. The integrative approach showed that changes in most target responses can be explained physiologically by oxidative stress responses. Increased oxidative damages (lipid peroxidation and DNA damage) and increased interaction between antioxidant enzymes (superoxide dismutase and catalase) are associated to increased time in frozen state and decreased swimming activity, growth rates and boldness. Under all stressful situations, larvae reduced energy-consuming behaviours (e.g. depleted exploration and swimming activity) likely to stabilize or compensate for the aerobic and anaerobic metabolisms. Despite being an active small pelagic fish, we concluded that the sensitive larval phase exhibited complex coping strategies to physiologically acclimate under thermal and hypoxic stress via behavioural responses.

Impact of anthropogenic noise on the survival and development of meagre (Argyrosomus regius) early life stages.

The growth of human populations has been driving an unprecedent and widespread increase in marine traffic, posing a real threat to marine biodiversity. Even though we are now aware of the negative effects of shipping noise exposure on fish, information about the impact on their early life stages continues to lack. Meagre (Argyrosomus regius) is a vocal fish that uses estuaries with high levels of anthropogenic noise pollution as both breeding areas and nurseries. Here, the effects of boat noise exposure on the development and survival of meagre larvae were studied. Embryos and larvae were exposed to either noise (boat noise playback) or control treatments (coils producing a similar electric field to the speakers) and hatching rate, survival rate, morphometric traits and stress-related biomarkers, at hatching and at 2 days-post-hatching (dph) were analyzed. Results showed no conclusive effects of the impact of boat noise playback, even though there was an increased lipid droplet consumption and a decrease in body depth at 2dph larvae under this stressor. The assessment of oxidative stress and energy metabolism-related biomarkers at hatching showed a marginal decrease in superoxide dismutase (SOD) activity and no changes in DNA damage or electron transport system activity (ETS), although it cannot be disregarded that those effects could only be visible at later stages of larval development. Whether these morphological and developmental results have implications in later stages remains to be investigated. Further studies with longer exposure and wild meagre could help deepen this knowledge and provide a better understanding of how anthropogenic noise can impact meagre early stages.

Evidence of contamination-associated damage in blue sharks (Prionace glauca) from the Northeast Atlantic.

Top predators such as most shark species are extremely vulnerable to amassing high concentrations of contaminants, but not much is known about the effects that the contaminant body burden imparts on these animals. Species like the blue shark (Prionace glauca) are very relevant in this regard, as they have high ecological and socioeconomic value, and have the potential to act as bioindicators of pollution. This work aimed to assess if differences in contaminant body burden found in blue sharks from the Northeast Atlantic would translate into differences in stress responses. Biochemical responses related to detoxification and oxidative stress, and histological alterations were assessed in the liver and gills of 60 blue sharks previously found to have zone-related contamination differences. Similar zone-related differences were found in biomarker responses, with the sharks from the most contaminated zone exhibiting more pronounced responses. Additionally, strong positive correlations were found between contaminants (i.e., As, PCBs, and PBDEs) and relevant biomarkers (e.g., damaged DNA and protective histological alterations). The present results are indicative of the potential that this species and these tools have to be used to monitor pollution in different areas of the Atlantic.

Assessment of contaminants in blue sharks from the Northeast Atlantic: Profiles, accumulation dynamics, and risks for human consumers.

Chemical pollution is a major threat to marine ecosystems, and top predators such as most shark species are extremely vulnerable to being exposed and accumulating contaminants such as metals and persistent organic pollutants (POPs). This work aimed to study the degree, composition, and the sources of contamination in the blue shark (Prionace glauca) inhabiting the Northeast Atlantic, as well as the potential risk faced by human consumers. A total of 60 sharks were sampled in situ aboard fishing vessels, and the concentrations of a set of metals and POPs were analysed in various tissues and complemented with stable isotope analyses. High levels of contaminants were found in most sharks sampled. The concentrations of most metals were higher in the muscle when compared with the liver. Regarding the dangers to consumers posed by the concentrations of arsenic (As), mercury (Hg), and lead (Pb), over 75% of the sharks presented muscle concentrations of at least one contaminant above the legal limits for human consumption, and a risk assessment determined that consumption of meat of these sharks exceeding 0.07 Kg per week could potentially expose human consumers to dangerous amounts of methylmercury (MeHg). Additionally, the assessment of single contaminants may lead to an underestimation of the risk for the human health. Finally, the overall accumulation of contaminants seems to be mostly influenced by the sharks' geographical distribution, rather than sex, size, or trophic level of their prey.

Are tolerance processes limiting the responses of Hediste diversicolor to cadmium exposure? A multimarker approach.

Cadmium (Cd) is considered a priority hazardous substance under the European Community Directive 2013/39 due to its ecotoxicity. The ragworm Hediste diversicolor (O.F. Müller, 1776), a common species in estuaries and coastal lagoons, plays an important ecological role in these ecosystems and is a suitable bioindicator of environmental chemical contamination. In this study, H. diversicolor was chosen as an ecotoxicological model with the aim of evaluating the responses to Cd contamination, considering a multi-biomarker approach (mortality, biometry, behaviour, Cd bioaccumulation, oxidative stress and damage, and energy metabolism). Also, the hypothesis of different tolerances resulting in different responses was evaluated, by collecting worms from three systems distinctly impacted by metal contamination (Mondego estuary, Óbidos Lagoon and Sado estuary - Portugal). Animals were exposed under laboratory conditions to cadmium (10, 50 and 100 µg/L), for 10 days. Significant differences were observed in responses amongst worms originating from the different sites. Organisms from the less impacted systems revealed greater effects on mortality, biomass decrease and burrowing behaviour, as well as higher bioaccumulation potential, after exposure to Cd. Biochemical and behaviour impairments were observed as a consequence of Cd exposure, although not in a concentration-dependant manner. The results obtained in this study reinforce the importance of integrating endpoint responses, at the individual and sub-individual levels, to assess potential changes induced by pollutants in the physiological status and fitness of H. diversicolor and help to predict what their ecological consequences might be.

Effect Biomarkers of the Widespread Antimicrobial Triclosan in a Marine Model Diatom.

The present-day COVID-19 pandemic has led to the increasing daily use of antimicrobials worldwide. Triclosan is a manmade disinfectant chemical used in several consumer healthcare products, and thus frequently detected in surface waters. In the present work, we aimed to evaluate the effect of triclosan on diatom cell photophysiology, fatty acid profiles, and oxidative stress biomarkers, using the diatom Phaeodactylum tricornutum as a model organism. Several photochemical effects were observed, such as the lower ability of the photosystems to efficiently trap light energy. A severe depletion of fucoxanthin under triclosan application was also evident, pointing to potential use of carotenoid as reactive oxygen species scavengers. It was also observed an evident favouring of the peroxidase activity to detriment of the SOD activity, indicating that superoxide anion is not efficiently metabolized. High triclosan exposure induced high cellular energy allocation, directly linked with an increase in the energy assigned to vital functions, enabling cells to maintain the growth rates upon triclosan exposure. Oxidative stress traits were found to be the most efficient biomarkers as promising tools for triclosan ecotoxicological assessments. Overall, the increasing use of triclosan will lead to significant effects on the diatom photochemical and oxidative stress levels, compromising key roles of diatoms in the marine system.

Scyliorhinus canicula (Linnaeus, 1758) metal accumulation: A public health concern for Atlantic fish consumers?

One of the most landed sharks in Portuguese fisheries is the lesser-spotted dogfish (Scyliorhinus canicula), which is ever-present in Portuguese fish markets and consumed as cheap fish protein source. The focus of this study was to evaluate element contamination in consumed tissues of Atlantic S. canicula, with the intent of safeguarding possible public health issues. A total of 74 specimens were analysed for metals and metalloids in the deeper white muscle and skin. Arsenic, zinc, iron and aluminium were the elements with higher mean values. There was a tendency for higher levels in the skin, with differences between life-stage and gender. Many individuals surpassed stipulated guideline limits for mercury and arsenic, posing a risk for human consumption (according to the health risk assessment performed for the average Portuguese fish consumption) or even for use in feed production. Besides the public health concern, this study also evidences troubling signs on marine contamination status.