Monitoring the evolution of deep-sea microplastic pollution in the Indo-Pacific using natural history collection holothurian specimens

While the production of plastic has been ever-increasing since the 1950s, little is known about the temporal dynamics of plastic pollution. Microplastics (less than 5 mm) represent the majority of total plastic pollution in terms of particle number. Microplastics stem mainly from the breakdown of larger plastic items, and can sink onto the ocean floor due to their own density or after biofilm formation. Consequently, microplastics accumulate on the ocean floor and particularly the deep-ocean floor, turning this poorly understood ecosystem into a major microplastic sink. Microplastics are easily ingested by a broad range of organisms, including benthic organisms. Holothurians (sea cucumbers) are benthic organisms found at all depths and latitudes. A vast majority of holothurian species are deposit-feeders, contributing significantly to bioturbation by ingesting between 9 and 82 kg per individual per year. Hence, we hypothesised that holothurians could be relevant organisms to monitor the evolution of benthic microplastic pollution. We developed a robust method to extract and quantify microplastics from holothurians by Pyrolysis-Gas Chromatography/Mass Spectrometry. Using an integrative taxonomy workflow, we identified time-series for two species of deep-sea holothurians from the Indo-Pacific (New Caledonia, Papua New-Guinea and Taiwan) Natural History Collection of the Paris Muséum National d’Histoire Naturelle, sampled between 1985 and today. Sixty specimens were analysed in order to model temporal trends for both species. Through this project, we aim to shed light on the evolution of microplastic pollution of the deep-ocean floor, an understudied ecosystem that harbours among the greatest biodiversity on Earth. This monitoring represents an essential step for informing policies aimed at preserving deep-ocean environments from anthropogenic impacts.