Effects of submerged marine debris on species composition and community characteristics of macrobenthos in the subtidal zone of Jeju Island, Korea

Abstract

Marine plastic debris, which does not readily decompose, remains present for a long time after sinking into the ocean. Increased levels of submerged marine debris can alter local species compositions and benthic community characteristics. However, most studies to date have focused on the physiology or mortality of specific species, while few have explored the composition and characteristics of species within the benthic community. Therefore, in this study, differences in species composition and distribution characteristics of macrobenthos were investigated in subtidal sediments and rocky areas covered with submerged marine debris to elucidate changes in the community characteristics of benthic ecosystems caused by debris. In July 2021, a survey was conducted via SCUBA diving in the subtidal zone of Jeju Island, which was divided into litter-present and litter-absent stations. Macrobenthos (> 1 mm in size) were collected in the subtidal sediment and rock areas using a can corer (0.025 m2) and quadrat (0.04 m2), respectively. In the subtidal sediment area, no significant difference was found in the particle size or organic content of sediment according to the presence or absence of litter (p > 0.05). The species number, diversity, and biomass of macrobenthos in the subtidal sediment area were higher in the presence of marine plastic debris, indicating that more species preferred adherent substrates such as litter over bare sediment. In the absence of plastic debris in the subtidal sediment area, the bivalve Solemya japonica was the most dominant (> 32% of total density). However, it decreased in density (2.7% of all macrobenthos) at the litter-present station of the subtidal sediment area, suggesting that submerged marine debris affects the species composition of macrobenthos. In addition, the opportunistic polychaete Nereis sp. was dominant at the litter-present station. In the subtidal rocky area, the species number, density, and diversity of macrobenthos showed no significant differences with the presence or absence of litter. However, the biomass of macrobenthos was high due to the presence of Magallana nippona at the litter-absent station (p < 0.05). We found that submerged marine debris affects the species composition of macrobenthos in subtidal areas with both sediment and rock substrates, suggesting that submerged marine debris can affect the structure of benthic ecosystems.