The present study investigated the spatial and temporal distribution, as well as the composition of coastal debris, with a particular focus on the effects of macroplastics on nematode communities in the sediments of the southern Caspian Sea. Samples were collected on ten sampling site during two season summer and winter of 2023. A total of 7283 and 7766 pieces of coastal debris were collected from the studied areas in summer and winter, respectively. Debris density ranged from 0.18 to 0.84 items/m2 and 0.17 to 1.04 items/m2 in summer and winter, respectively. Generally, the results showed the highest concentration at the central stations and the lowest at the eastern stations. Plastic items, especially plastic bags, predominated the debris, constituting 60.35 % and 60.82 % of the total debris collected in summer and winter, respectively. Based on Clean Coast Index (CCI), sampling sites ranged clean to dirty and clean to extremely dirty in summer and winter, respectively. In the laboratory, the impact of single-use plastic bags on nematode community characteristics was investigated experimentally in a microcosm study over 5, 10, 20, 30, and 40 days in five separate aquariums. The results showed that macroplastics on sediment significantly (p < 0.05) reduced sediment oxygen reduction potential (ORP) among the various times and treatments and altered the total nematode community. Additionally, total nematode density and diversity indices significantly decreased under macroplastics treatments each time (p < 0.05). These findings highlight the detrimental effects of marine debris on ecosystem health.
Keywords: Caspian Sea; Community structure; Free living nematode; Macroplastic; Marine debris.
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