Detection of Microplastic contamination in shallow marine habitats using solitary ascidians: Influence of morphology and habitat in a tropical bay, SW Atlantic

The ubiquity of microplastics (MP) in marine ecosystems and their biological uptake has become a major global concern. Many papers indicate MP ingestion by marine organisms, but few studies address the role of morphological characteristics of species on MP ingestion and retention in filter-feeding species. This study investigates the presence of MP in four ascidians species as models: Styela plicata, Phallusia nigra, Microcosmus exasperatus and Herdmania pallida. They are compared in relation to the shape (simple or branched) and number of oral tentacles, and the presence of branchial folds (from none to 18). Morphology, here, were used as a proxy for mechanisms that may prevent MP ingestion. Furthermore, we compared the concentration of MP among species from sites with and without harbor, and during summer and winter seasons. Specimens were collected in the Ilha Grande Bay, where they are widely distributed in natural and artificial substrates. Microplastics were extracted by density separation, quantified, and categorized by granules, fibers and fragments. The morphological structure present in S. plicata, with simple tentacles and branchial folds retained significantly more MP particles than all other species. This suggests that tentacles morphology and the presence of branchial folds may influence MP capture. Specimens near harbor areas and sampled during winter showed higher abundance of MP, reflecting association of plastic pollution with shipping and unsustainable tourism activities. This is the first assessment of MP contamination in ascidians from tropical bays and from natural environments. Its association with morphology, opens new perspectives for studies dealing with mechanics of filtering activity of marine invertebrates.