Beyond sea urchins: sea stars and brittle stars as welfare-friendly models in marine ecotoxicology.

The field of marine ecotoxicology is based on a limited range of model organisms that incompletely represent sea and ocean biodiversity and ecological function. Although echinoderms have been recognised as valuable test organisms, ecotoxicological research predominantly focuses on sea urchins, with comparatively limited attention given to other classes. This review synthesises ecotoxicological studies published over the past two decades on sea stars (Asteroidea) and brittle stars (Ophiuroidea) taking into consideration contaminants investigated, the biological endpoints applied and their suitability as model organisms. An analysis of 74 studies reveals a bias towards trace elements and bioaccumulation analysis, while organic pollutants, emerging contaminants and mixture toxicity remain underrepresented. Immune and cellular biomarkers are frequently employed, whereas behavioural, developmental, reproductive and other functional endpoints are used less often. Heatmap analyses highlight disparities in contaminant/endpoint combinations and taxonomic coverage, with brittle stars particularly underrepresented in studies. It is important to note that some of the endpoints reported for asteroid and ophiuroid are compatible with non-lethal or minimally invasive methodologies. On this basis, behavioural assays are identified as a promising welfare-oriented approach for repeated measures toxicity testing. Overall, the integration of asteroids and ophiuroids into ecotoxicological bioassay batteries could enhance ecological relevance, phylogenetic breadth and ethical alignment in marine pollution assessment.