Microplastic ingestion in wild zoanthids: first evidence and a global meta-analysis on cnidarian

Nowadays, microplastics (MPs) are widespread across the planet and are recognized as a major threat to life on Earth. This study investigates the prevalence of microplastics in three species of zoanthids (Palythoa mutuki, Palythoa tuberculosa, and Zoanthus sansibaricus), sediment, and surface water samples collected from four rocky shores of Gujarat state, India. The extraction of MPs was carried out using a standard method. A total of 886, 389, and 128 MP particles were recorded, with an average abundance of 9.99 ± 6.29 MPs/g, 11.36 ± 4.03 MPs/kg, and 0.93 ± 0.52 MPs/L in zoanthids, sediment, and surface water, respectively. The highest MP contamination was found in Z. sansibaricus, followed by P. mutuki and P. tuberculosa. Contamination varied significantly between study sites and species of zoanthids (H (χ²) = 9.45, p < 0.05, df = 59), with the highest MP abundance recorded in Dwarka. Sediment and surface water samples showed highest levels of MPs in Sutrapada. Physical characterization revealed that fibers were the most common shape of MPs, and particles were predominantly < 1 mm in size. Blue, black, and red colored MPs were found dominantly. The dominant polymer types identified were polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), and polyurethane (PU). PCA results show that pH, sediment, and water quality are the main environmental drivers influencing zoanthid ecology and MP contamination, while temperature and salinity have weaker or negative effects. Pollution indices revealed medium contamination in study site Dhamlej (H = 125.71, PRI = 217.79) and very high contamination in study sites Veraval, Dwarka, and Sutrapada. A meta-analysis reviewed MP contamination in different faunal groups of cnidarians; jellyfish Pelagia noctiluca showed the highest contamination, while sea anemone Edwardsia meridionalis had the lowest. Fibers were the most common MP shape, with 0.5-3 mm sizes and red, black, and blue colors dominating. Polyethylene (PE) was the most abundant polymer, with variations in polymer dominance among cnidarian groups. Therefore, understanding the impacts of microplastic pollution on zoanthids is critical, as their decline could have cascading effects on reef ecosystem health and resilience.