Pollution in the seas and oceans is a global problem, which highlights emerging pollutants and plastics, specifically microplastics (MPs), which are tiny (1 μm to 5 mm) ubiquitous plastic particles present in marine environments that can be ingested by a wide range of organisms. Holothurians are benthic organisms that feed on sediment; therefore, they can be exposed to contaminants present in the particles they ingest. The objective was to evaluate the effects of human activity on Holothuria tubulosa through the study of biomarkers. Specimens were collected in three different areas throughout the island of Eivissa, Spain: (1) a highly urbanized area, with tourist uses and a marina; (2) an urbanized area close to the mouth of a torrent; (3) an area devoid of human activity and considered clean. The results showed a higher presence of microplastics (MPs) in the sediments from the highly urbanized area in relation to the other two areas studied. Similarly, a higher number of MPs were observed in the digestive tract of H. tubulosa from the most affected area, decreasing with the degree of anthropic influence. Both in the sediment and in the holothurians, fibers predominated with more than 75% of the items. In the three areas, mesoplastics were analyzed by means of FTIR, showing that the main polymer was polypropylene (27%) followed by low-density polyethylene (17%) and polystyrene (16%). Regarding the biomarkers of oxidative stress, the intestine of H. tubulosa from the most impacted areas showed higher catalase, superoxide dismutase (SOD), glutathione reductase (GRd), and glutathione S-transferase (GST) activities and reduced glutathione (GSH) levels compared to the control area. The intermediate area only presented significant differences in GRd and GST with respect to the clean area. The activities of acetylcholinesterase and the levels and malondialdehyde presented similar values in all areas. In conclusion, human activity evaluated with the presence of MPs induced an antioxidant response in H. tubulosa, although without evidence of oxidative damage or neurotoxicity. H. tubulosa, due to its benthic animal characteristics and easy handling, can be a useful species for monitoring purposes.

Human activities increasingly threaten marine ecosystems through rising waste and temperatures. This study investigated the role of plastics as vectors for Vibrio bacteria and the effects of temperature on the marine sponge Sarcotragus spinosulus. Samples of plastics and sponges were collected during July, August (high-temperature period), and November (lower-temperature period). Bacterial growth and sponge responses were analysed using biochemical biomarkers. The results revealed a peak in colony-forming units (CFU), particularly of Vibrio alginolyticus, on plastics and sponges in August, followed by a decrease in November. In August, CFU counts of Vibrio spp. were significantly higher in sponges with poor external appearance (characterized by dull coloration and heavy epiphytic growth) but returned to levels observed in healthy sponges by November. Microplastics were detected in the tissues of both sponge groups, with higher concentrations found in affected specimens. Biomarker analyses revealed increased lysozyme, glutathione S-transferase, catalase, and superoxide dismutase activities in healthy sponges during August, while malondialdehyde levels, indicating oxidative damage, were higher in affected sponges. In conclusion, affected sponges exhibited elevated CFU counts of Vibrio spp. and reduced antioxidant and detoxification responses under elevated temperatures. These findings suggest that combined impacts of plastics and warming may pose significant risks to S. spinosulus in the context of global climate change.

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.

Bothus podas (wide-eyed flounder) is a benthic flatfish likely exposed to microplastic (MP) pollution. We investigated MP ingestion and associated physiological effects in wild B. podas collected from Mallorca (Balearic Islands), Spain. Markers of oxidative stress, detoxification, and immunity were quantified in intestinal, hepatic, and splenic tissues. MPs were observed in the gastrointestinal tracts of 87.5% of the 24 specimens analyzed, with an average of 3.8 ± 0.6 items per fish. Fiber-type MPs predominated in both the gastrointestinal tract (69.6%) and sediment samples (97%). Additionally, micro-Fourier transform infrared spectroscopy analysis confirmed that the majority of ingested MPs were composed of polyethylene, polypropylene, and polyester. Fish were categorized into low (<3 items) and high (≥3 items) MP groups based on the median number of plastic items found in the gastrointestinal tract to assess sublethal impacts. In the gut, high-MP fish exhibited significantly elevated activities of detoxification enzymes: ethoxyresorufin-O-deethylase (phase I) and glutathione s-transferase (phase II), along with increased antioxidant enzyme superoxide dismutase and inflammatory myeloperoxidase. Gut catalase and malondialdehyde (MDA) were not significantly different between groups. In liver tissues, no biomarkers differed significantly with MP exposure. In the spleen, lysozyme and alkaline phosphatase activities were significantly higher in high-MP fish, while splenic MDA remained unchanged. These results indicate that gastrointestinal MP exposure triggers local oxidative stress responses and systemic immune activation in B. podas. Overall, ingestion of environmentally relevant MP levels elicited detoxification and inflammatory responses without significant increases in MDA, an indicator of oxidative damage, highlighting the physiological stress imposed by plastic pollution on benthic fish.