Tracking Anthropogenic Particles with Sea Urchins: Paracentrotus lividus as a Bioindicator in the Balearic Islands

Interactions between benthic invertebrates and anthropogenic particles, such as microplastics, are increasingly being reported worldwide, and especially in the Mediterranean Sea. In this study, we monitor the potential of the benthic sea urchin Paracentrotus lividus (Lamarck, 1816), as a bioindicator for microplastic pollution in coastal waters of Mallorca, Balearic Islands. Specimens were collected across three ecologically distinct sites, Port de Sóller (urban), Alconàsser (semiurban), and Cala Blava (marine reserve), throughout four seasons to evaluate spatial and temporal variation in anthropogenic particle ingestion ($\mathbf{n}=\mathbf{9 6}$). In addition to specimens of P. lividus, sediments ($\mathbf{n}=\mathbf{2 4}$) were also collected to evaluate the presence of anthropogenic particles. Results showed the occurrence of anthropogenic particles across all locations and seasons with $51 \%$ of P. lividus individuals surveyed containing anthropogenic particles. Cala Blava had the highest overall frequency ($59.4 \%$), followed by Pt. Soller ($50.0 \%$) and Alconàsser ($\mathbf{4 3. 8 \%}$). In terms of sediment analyses, an average anthropogenic particle concentration of $0.036 \pm 0.010$ items/g, within the Port de Sóller showed the highest levels ($0.05 \pm 0.02$ items/g), followed by Alconàsser ($0.04 \pm 0.02$ items $/ \mathrm{g}$) and Cala Blava ($0.01 \pm 0.005$ items $/ \mathrm{g}$). These findings highlight the potential of $\boldsymbol{P}$. lividus as a bioindicator species for monitoring localised microplastic pollution and contribute to understanding how anthropogenic pressures and seasonal dynamics influence plastic exposure in coastal benthic ecosystems.