Biomarker responses in gills of Holothuria tubulosa from coastal waters of Eivissa Island (Western Mediterranean, Spain) to anthropogenic impact

Marine pollution from microplastics (MPs) and polycyclic aromatic hydrocarbons (PAHs) can affect benthic consumers. The aim was to quantify MPs and seven >3-ringed PAHs, identify polymer types by μ-ATR-FTIR, and assess antioxidant and detoxification biomarkers in gills of Holothuria tubulosa at three Eivissa Island sites: Sant Antoni (highly anthropogenic impacted site, SA), Santa Eulària (moderately impacted site, SE) and Pou des Lleó (minimally impacted site, PL). A total of 95 MPs were found in gills (SA: 44; SE: 32; PL: 19), averaging 4.4 ± 0.72, 3.20 ± 0.51 and 1.90 ± 0.43 MPs per individual at SA, SE and PL. Higher MP amounts occurred in sediment and seawater at the highly impacted site as compared to the moderately and minimally impacted sites. μ-ATR-FTIR identified polyester, polypropylene and HDPE as the dominant polymers in gill items. Among seven PAHs, indeno[1,2,3-c,d]pyrene (InP), chrysene (Chr) and benzo[a]anthracene (BaA) were quantified in sediments (InP: 1.18 ± 0.01 μg/kg at SA and 1.04 ± 0.06 μg/kg at PL; Chr: 2.90 ± 0.90 μg/kg at SA; BaA: 3.70 ± 0.70 μg/kg at SA and 2.98 ± 0.08 μg/kg at SE). Antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GRd) and reduced glutathione (GSH) increased at the highly impacted site (CAT p = 0.003; SOD p = 0.045; GRd p = 0.023; GSH p < 0.001). The activity of glutathione S-transferase (p = 0.006) and ethoxyresorufin-O-deethylase (p < 0.001) also increased, while that of glutathione peroxidase and malondialdehyde did not differ. Results indicate site-dependent MP and PAH increases that are correlated with enhanced oxidative stress and detoxification responses in H. tubulosa, supporting its use as a coastal bioindicator.