Large plastic debris dumps: New biodiversity hot spots emerging on the deep-sea floor

Abstract

Macroplastic debris recorded in the Mariana Trench and accumulated on some deep-sea canyons worldwide has aroused great public concerns. Large plastic debris dumps found in canyons of the Xisha Trough, South China Sea have become hot spots for deep-sea pollution, with 1 order of magnitude higher abundance than in other investigated canyons. Here we adopted an integrative specimen-based approach to examine macroplastic items from large debris dumps in the Xisha Trough and comparative items from continental shelves with rare macroplastics. On the investigated items, we found an epibenthic ecosystem with relatively high species diversity, comprised of 49 mm-sized fungi and invertebrate species dominated by scyphozoan polyps and brachiopod juveniles according to inhabiting density. These large dumps are functioning as new biodiversity hot spots hosting endemic species like soft corals or aplacophoran molluscs, providing a spawning habitat for gastropods and even specialized parasitic flatworms, and can be inferred as potential scattered regional sources releasing deep-sea coronate jellyfish. We hypothesize that macroplastics can boost population extension of sessile and some free-living (Mollusca) invertebrates and affect the deep-sea benthic-pelagic coupling process. The baseline of associated organisms needs to be set up and monitored in more canyons, where debris is transported to and accumulated at the highest density.