Silver nanoparticles represent a threat to biota and have been shown to cause harm through a number of mechanisms, using a wide range of bioassay endpoints. While nanoparticle concentration has been primarily considered, comparison of studies that have used differently sized nanoparticles indicate that nanoparticle diameter may be an important factor that impacts negative outcomes. In considering this, the aim of the present study was to determine if different sizes of silver nanoparticles (AgNPs; 10, 20, 40, 60 and 100 nm) give rise to similar effects during embryogenesis of Mediterranean sea urchins Arbacia lixula and Paracentrotus lividus, or if nanoparticle size is a parameter that can modulate embryotoxicity and spermiotoxicity in these species. Fertilised embryos were exposed to a range of AgNP concentrations (1–1000 µg L⁻¹) and after 48 h larvae were scored. Embryos exposed to 1 and 10 µg L⁻¹ AgNPs (for all tested sizes) showed no negative effect in both sea urchins. The smaller AgNPs (size 10 and 20 nm) caused a decrease in the percentage of normally developed A. lixula larvae at concentrations ≥50 µg L⁻¹ (EC₅₀: 49 and 75 μg L⁻¹, respectively) and at ≥100 µg L⁻¹ (EC₅₀: 67 and 91 μg L⁻¹, respectively) for P. lividus. AgNPs of 40 nm diameter was less harmful in both species ((EC₅₀: 322 and 486 μg L⁻¹, for P. lividus and A. lixula, respectively)). The largest AgNPs (60 and 100 nm) showed a dose-dependent response, with little effect at lower concentrations, while more than 50% of larvae were developmentally delayed at the highest tested concentrations of 500 and 1000 µg L⁻¹ (EC₅₀(100 nm); 662 and 529 μg L⁻¹, for P. lividus and A. lixula, respectively. While AgNPs showed no effect on the fertilisation success of treated sperm, an increase in offspring developmental defects and arrested development was observed in A. lixula larvae for 10 nm AgNPs at concentrations ≥50 μg L⁻¹, and for 20 and 40 nm AgNPs at concentrations >100 μg L⁻¹. Overall, toxicity was mostly ascribed to more rapid oxidative dissolution of smaller nanoparticles, although, in cases, Ag⁺ ion concentrations alone could not explain high toxicity, indicating a nanoparticle-size effect.

Copper-based nanoparticles (as Cu₂O) are a key component in marine antifouling paints and, as coatings degrade, release nanoparticles that can affect a wide range of non-target organisms. This study investigates the impact of Cu₂O nanoparticles on the early development of urchins Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis, and benchmarks their toxicity against similarly sized Cu and CuO nanoparticles and ionic copper. Concentration-dependent toxicity was noted for all forms of copper at concentrations in the 1 to 5000 µg L⁻¹ range. EC₅₀ values after Cu₂O exposure indicated that A. lixula (99 µg L⁻¹) was generally more sensitive than the other two species, with EC₅₀ values of 371 µg L⁻¹ and 606 µg L⁻¹ noted for S. granularis and P. lividus, respectively. The same trend across species was noted for both Cu and CuO, although these nanoparticles generally showed higher EC₅₀ values, indicating lower toxicity compared to Cu₂O. LC₅₀ values qualitatively parallel the corresponding EC₅₀ values, with Cu₂O consistently the most toxic, while Cu was less harmful, and CuO did not reach LC₅₀ at any concentration. Again, greatest lethality was noted in A. lixula. While copper ion release from Cu was much greater than from CuO and Cu₂O, the latter showed similar or greater toxicity to developing embryos compared to Cu. This indicates that copper ions are not the sole driver of toxicity of Cu₂O, but there may also be a contribution derived from Cu₂O redox activity within cells or at membranes that negatively impact oxidative stress defence mechanisms and metabolic pathways.

Clavelina oblonga is an invasive tropical tunicate recently introduced into the Adriatic Sea as a consequence of globalization and climate change. Mussel aquaculture sites provide an ideal environment for this colonial ascidian, where it has recently become the dominant fouling species. This study represents the first investigation of its biological and physical characteristics, as well as its proximal, fatty acid, macroelement, trace element, and toxic metal composition. The entire-tissue chemical composition of C. oblonga resulted in 95.44% moisture. Its composite structure revealed several strong peaks, attributed to O-H, C-H, C-N, and C=O stretching, along with cellulose components overlapping with proteins and carbohydrates. The major fatty acids were palmitic, stearic, and docosahexaenoic acid, followed by docosanoic, elaidic, linoleic, and myristic acid. The saturated fatty acids, polyunsaturated fatty acids, and monounsaturated fatty acids comprised 51.37, 26.96, and 15.41% of the total fatty acids, respectively. Among the analysed trace and macroelements, aluminium and sodium were predominant. C. oblonga exhibited different concentrations of toxic metals, such as arsenic and lead, compared to fouled mussels in the Istria region. It appears that the tunicate has adapted to the environmental conditions of the Adriatic, reaching its maximum spread and biomass in mid-autumn. There is a strong possibility that C. oblonga could colonize and establish itself permanently in the Adriatic. This would have a strong negative impact on shellfish farming, the structure of the ecosystem, plankton biomass, and the distribution of other marine species. However, it also represents a biomass resource with high potential of utilization in different industries.

To evaluate the effects of mussel meal, as a sustainable ingredient for fish feed, on the growth, health status, proximate composition, and fatty acid profile of gilthead seabream, mussel meal was included in commercial feed formulations. Sunflower oil (2%) was used as a binding agent. Four groups of gilthead seabream were fed either with control feed (commercial feed, commercial feed and sunflower oil) or mussel-meal-supplemented formulations (commercial feed, sunflower oil, and 2.5 or 5% mussel meal) for six weeks. In this experiment, a total of 180 specimens of gilthead seabream juveniles were included. The initial weight and length of the gilthead seabream specimens were, on average, 13.04 g and 9.57 cm, respectively. The average temperature of the seawater ranged between 25 and 26 °C during the experiment. The results of this study indicated a higher relative weight gain and a slightly lower feed conversion ratio in the control group fed with commercial feed, probably because of macronutrient imbalances introduced by the addition of mussel meal and sunflower oil. The groups fed with mussel-supplemented diets had a slightly lower crude protein content compared to the group fed with a commercial diet. The addition of sunflower oil and mussel meal decreased the saturated fatty acid content while increasing the monounsaturated and polyunsaturated fatty acid content compared to the control group. However, the high content of DHA and EPA in the mussel meal resulted in a proportional increase of these fatty acids in the muscle tissue of gilthead seabream, although the overall effect was not statistically significant. The findings of this study suggest that mussel meal is a promising source of protein and lipids for sustainable fish feed production, but under the experimental setup, mussel meal did not act as an attractant for increasing fish feed intake during the summer conditions.