The use of marine invertebrates in ecotoxicology is important for an integrated approach which takes into consideration physiological responses and chemical levels in environmental matrices. Standard protocols have been developed and organisms belonging to different trophic levels are needed as model organisms to evaluate toxicant bioavailability and assess their impact on marine biota. The calanoid copepod Acartia tonsa is commonly used in ecotoxicology due to its widespread distribution and well-studied biology. However, different strains coming from various geographical areas are available, and possible variations in physiological characteristics raise concerns about the comparability of ecotoxicological results. This study compares the life cycle assessment and sensitivity of Adriatic and Baltic strains of A. tonsa exposed to nickel (Ni²⁺) in standardized acute and semi-chronic tests. Life cycle assessments revealed differences in egg production, egg-hatching success, and naupliar viability between the strains. The acute toxicity test demonstrated the significantly higher sensitivity of Adriatic strain nauplii to Ni²⁺ compared to the Baltic strain, whereas the semi-chronic test showed no significant difference in sensitivity between the strains. These findings suggest that while strain-specific differences exist in different geographical populations, responses to toxicants are not significantly different. Particularly, the semi-chronic assessments with both A. tonsa strains emphasized the robustness of this species as a model organism in ecotoxicology.

Seagrasses are important components of coastal ecosystems and represent a source of chemically diverse natural products with potentially relevant biological activities. This study aimed to characterize the biochemical and metabolomic profiles of leaves and rhizomes of the Mediterranean seagrass Cymodocea nodosa and to compare the biological activity of extracts from the two tissues across different marine organisms. Hydroalcoholic extracts were characterized by biochemical assays and untargeted liquid chromatography–high-resolution mass spectrometry, while biological responses were assessed using Aliivibrio fischeri, Phaeodactylum tricornutum, Dunaliella tertiolecta, Acartia tonsa, and the fouling serpulid Ficopomatus enigmaticus. Leaves and rhizomes differed in their biochemical characteristics but shared most putatively annotated metabolites, including phenolic acids, flavonoids, lipid-derived metabolites, and amino acid derivatives. Semi-quantitative analysis revealed tissue-associated differences in relative LC-HRMS signal intensities. Biological responses were species- and endpoint-dependent, with F. enigmaticus showing the highest sensitivity, particularly to the rhizome extract (EC50 = 48.8 mg/L), whereas the other organisms generally responded at higher concentrations. Overall, these findings highlight tissue-associated chemical and biological differences in C. nodosa extracts and identify rhizomes as particularly interesting for further investigation into the relationships between seagrass metabolites and fouling-related biological responses.