Sponges as Sentinels of Coastal Water Quality and Microplastic Contamination in Mallorca, Western Mediterranean

Marine sponges (Phylum Porifera) are ecologically important, sessile filter feeders that play key roles in benthic ecosystems and are increasingly recognized as sensitive bioindicators of environmental change. Their ability to integrate localized conditions over time makes them particularly suited for detecting chronic stressors such as plastic pollution. The Mediterranean Sea, despite being a hotspot for sponge diversity, is heavily impacted by anthropogenic pressures and ranks among the most plastic-contaminated marine regions globally. However, the specific biological effects of plastic exposure on sponge populations in this region remain poorly understood. The ESQuAMa project aims to assess sponge diversity and evaluate their physiological responses to microplastic (MP) and nanoplastic (NP) contamination to establish their role as bioindicators of coastal water quality in Mallorca. Sponges were surveyed across sites along a defined gradient of human impact. Species composition, number of species, and habitat associations were documented. Selected species were analyzed for MP and NP content using spectroscopic and imaging techniques. Oxidative stress biomarkers, including antioxidant enzyme activities and indicators of lipid peroxidation, were quantified to assess sub-lethal physiological responses. By linking sponge distribution patterns and physiological stress responses to plastic contamination levels, this study provides new insights into the vulnerability and ecological function of Mediterranean sponges. The results contribute to the development of sponge-based bioindication frameworks and support the integration of benthic invertebrates into long-term coastal monitoring strategies, particularly in areas facing increasing anthropogenic pressure.