Plastic pollution and invasive species are recognised as pervasive threats to marine biodiversity. However, despite the extensive on-going research on microplastics’ effects in the biota, knowledge on their combination with additional stressors is still limited. This study investigates the effects of polyamide microplastics (PA-MPs, 1 mg/L), alone and in combination with the toxic exudate from the invasive red seaweed Asparagopsis armata (2%), after a 96 h exposure, in the mussel Mytilus galloprovincialis. Biochemical responses associated with oxidative stress and damage, neurotoxicity, and energy metabolism were evaluated in different tissues (gills, digestive gland, and muscle). Byssus production and PA-MP accumulation were also assessed. Results demonstrated that PA-MPs accumulated the most in the digestive gland of mussels under PA-MP and exudate co-exposure. Furthermore, the combination of stressors also resulted in oxidative damage at the protein level in the gills as well as in a significant reduction in byssus production. Metabolic capacity increased in both PA-MP treatments, consequently affecting the energy balance in mussels under combined stress. Overall, results show a potential increase of PA-MPs toxicity in the presence of A. armata exudate, highlighting the importance of assessing the impact of microplastics in realistic scenarios, specifically in combination with co-occurring stressors, such as invasive species.

Microbiological contamination of bivalve molluscs is one of the major concerns inherent to food safety, thus depuration is frequently needed to assure food safety levels associated with their consumption. Salinity plays an important role in the metabolic activity of bivalves and as such can influence their depuration capacity. This study aimed to evaluate the effect of salinity (25, 30, 35 and 40) on the efficiency of the depuration process, along with the quality and shelf-life of Crassostrea gigas. For this, a 24-h depuration was carried out, followed by a storage period at 5 ± 1 °C for six days. Microbiological analyses and biochemical parameters related to oxidative stress response were analysed. Escherichia coli load was reduced in only 24 h, disregarding the salinity of the system. After the shelf-life period, the activity of the antioxidant defences at salinities 35 and 40 is higher but is still not sufficient to avoid lipid peroxidation. Over time, there is a decrease in oyster metabolism probably due to being chilled and to the action of exposure to air. In sum, this study suggests salinities between 25 and 30 as preferential for the depuration process of C. gigas and subsequent quality during shelf-life.

Microplastic pollution, global warming, and invasive species are known threats to marine biota, but the impact of their simultaneous exposure is still not well understood. This study investigated whether the toxic effects posed by the invasive red seaweed Asparagopsis armata exudate (2%) to the mussel Mytilus galloprovincialis are amplified by a 96 h exposure to increased temperature (24 °C) and polyethylene microplastics (PE-MPs, 1 mg/L). Biochemical (neurotoxicity, energy metabolism, oxidative stress, and damage) and physiological (byssal thread production) responses were evaluated. The number of produced byssus greatly decreased under concomitant exposure to all stressors. The antioxidant defences were depleted in the gills of mussels exposed to temperature rises and PE-MPs, regardless of exudate exposure, preventing oxidative damage. Moreover, the heat shock protein content tended to decrease in all treatments relative to the control. The increased total glutathione in the mussels’ digestive gland exposed to 24 °C, exudate, and PE-MPs avoided oxidative damage. Neurotoxicity was observed in the same treatment. In contrast, the energy metabolism remained unaltered. In conclusion, depending on the endpoint, simultaneous exposure to A. armata exudate, PE-MPs, and warming does not necessarily mean an amplification of their single effects. Studies focusing on the impact of multiple stressors are imperative to better understand the underlying mechanisms of this chronic exposure.

Ocean warming and biological invasions are among the most pervasive factors threatening coastal ecosystems with a potential to interact. Ongoing temperature rise may affect physiological and cellular mechanisms in marine organisms. Moreover, non-indigenous species spread has been a major challenge to biodiversity and ecosystem functions and services. The invasive red seaweed Asparagopsis armata has become successfully established in Europe. Its exudate has been considered deleterious to surrounding native species, but no information exists on its effect under forecasted temperature increase. This study evaluated the combined effects of temperature rise and A. armata exudate exposure on the native mussel Mytilus galloprovincialis. Oxidative stress, neurophysiological and metabolism related biomarkers were evaluated after a 96 h-exposure to exudate (0% and 2%) under present (20 °C) and warming (24 °C) temperature scenarios. Short-term exposure to A. armata exudate affected the oxidative stress status and neurophysiology of the mussels, with a tendency to an increasing toxic action under warming. Significant oxidative damage at protein level was observed in the digestive gland and muscle of individuals exposed simultaneously to the exudate and temperature rise. Thus, under a climate change scenario, it may be expected that prolonged exposure to the combined action of both stressors may compromise M. galloprovincialis fitness and survival.

Bivalve mollusks represent a nutritious source with a low environmental impact; as a result, they are one of the most attractive aquaculture options. Advances in microencapsulation technology offer great potential to face key bivalve nutrition problems, and an alga-based microencapsulated diet can turn enriched bivalves into potential functional foods. The central goal of this study was the evaluation of food intake as a function of particle size and microalga content following the supply of four microencapsulated diets, incorporating as core material Nannochloropsis sp. or Tetraselmis sp. in 20 or 40 µm diameter pellets (diets N20, T20, N40, and T40, respectively) in five bivalve species (Magallana gigas, Solen marginatus, Ruditapes decussatus, Ruditapes philippinarum, and Cerastoderma edule). Overall, all tested diets were easily ingested, although food intake was higher for N20 (except for the S. marginatus, which showed a higher rate for the diet T40). Concerning a size-related analysis, C. edule and S. marginatus favored, respectively, smaller and bigger pellet-sized diets, with no signs of selectivity for microalga species. The diet T20 was the lesser ingested, except for C. edule. This knowledge enables a better selection of feed with appropriate and species-adjusted profiles, contributing to the optimization of microencapsulated diets for bivalve rearing and a better final product.