Nearshore biogenic habitats are known to trap sediments, and may therefore also accumulate biofouled, non-buoyant microplastics. Using a current-generating field flume (TiDyFLOW), we experimentally assessed the mechanisms of microplastic trapping of two size classes, 0.5 mm and 2.5 mm particle size, by three contrasting types of biogenic habitats: 1) seagrasses, 2) macroalgae, and 3) scleractinian corals. Results showed that benthic organisms with a complex architecture and rough surface – such as hard corals – trap the highest number of microplastics in their aboveground structure. Sediment was however the major microplastic sink, accumulating 1 to 2 orders of magnitude more microplastics than the benthic structure. Microplastic accumulation in the sediment could be explained by near-bed turbulent kinetic energy (TKE), indicating that this is governed by the same hydrodynamic processes leading tosediment trapping. Thus, the most valuable biogenic habitats in terms of nursery and coastal protection services also have the highest capacity of accumulating microplastics in their sediments. A significantly larger fraction of 0.5 mm particles was trapped in the sediment compared to 2.5 mm particles, because especially the smaller microplastics are entrained into the sediment. Present observations contribute to explaining why especially microplastics smaller than 1 mm are missing in surface waters.
Bibliographical noteKAUST Repository Item: Exported on 2021-02-11
Acknowledged KAUST grant number(s): OSR-2019-CPF-4107.1
Acknowledgements: This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR-2019-CPF-4107.1. We thank Ramzi Aljahdali from the Coastal and Marine Resources Core Lab (CMOR) for logistical assistance, and Amr Gusti, Walid Aljahdali and Hassan Niazi for their assistance with the field flume experiments. Hanan Almahasheer, Vincent Saderne, Michael Cusack and Oscar Serrano are thanked for their assistance with collecting the sediment cores in seagrass meadows. Three anonymous reviewers are thanked for their constructive criticism which substantially improved the manuscript. Symbols of organisms used in the graphical abstract and Figure 1 and 5 are courtesy of the Integration and Application Network, University of Maryland Center for Environmental Science (ian.umces.edu/symbols/). The data and analyses of this study are available at dx.doi.org/10.4121/13469190.