Predicting microplastic dynamics in coral reefs: presence, distribution, and bioavailability through field data and numerical simulation analysis

Understanding distribution and bioavailability of microplastics is vital for conducting ecological risk assessments (ERA) and developing mitigation strategies in marine environments. This study couples in situ data from Lizard Island (Great Barrier Reef) and numerical modelling and simulations to determine microplastic abundances in abiotic (water and sediment) and biotic (planktivorous fish, sea squirts, sponges, corals, and sea cucumbers) compartments and predict their trajectories within this ecosystem. Results show microplastics predominantly (75%) originate from beached plastics from nearby islands and coastal areas, dispersing northward without local entrapment and settlement likely occurring on northern beaches (> 50%), including Papua New Guinea. Concentrations increased by three orders of magnitude with depth, with distinct profiles: surface waters contained more fragments and low-density polymers at concentrations of < 1 microplastics m^-3, and deeper layers more fibres and high-density polymers, with concentrations peaking at the seafloor at > 100 microplastics m^-3. Reflecting ecological and physiological traits of each taxon, fish exhibited microplastic contamination levels nearly twice that observed in invertebrates, and while polymers and colours had no stronger evidences on influencing bioavailability, shape and size did, with fish more susceptible to contamination by microplastic fibres and all taxa to smaller-sized microplastic particles.