Canopy Accumulation: Are Seagrass Meadows a Sink of Microplastics?

Abstract

A growing body of research is documenting the accumulation of microplastics within marine sediments around the world. The hydrodynamic influences of seagrasses in coastal environments are shown to increase sedimentation of finer particles and as a result there has been speculation that this attribute will lead to seagrass meadows acting as a site of elevated microplastic contamination. To date a range of localised studies have provided conflicting answers to this hypothesis. Seagrass meadows provide multiple ecosystem services including vital support roles for a range of fisheries; therefore, there are considerable human health implications for understanding their role as sinks of microplastics. This research investigated the abundance and diversity of microplastics present in temperate North Atlantic seagrass meadow sediments relative to unvegetated sediments and examined how they correlate with the meadow structure and the sediment type. We also placed this data in the context of the current knowledge of microplastics in seagrass sediments through a global meta-analysis of published data. Eight seagrass meadows and adjacent unvegetated sites around the UK were sampled to test for the abundance of microplastic particles in the sediment. Microplastics were found in 98% of the samples, with fibres making up 91.8% of all microplastics identified. Abundance was recorded to overall be 215 ± 163 microplastic particles (MP) kg−1 Dry Weight (DW) of sediment in seagrass and 221 ± 236 MP kg−1 DW of sediment in unvegetated habitats. There were no significant differences found between the number of MP with respect to vegetation. We report evidence of the almost ubiquitous contamination of seagrass sediments with microplastics both in the UK and globally but find that the contamination reflects a general build-up of microplastics in the wider environment rather than becoming concentrated within seagrass as an enhanced sink. Microplastic build up in sediments is hypothesised to be the result of local hydrodynamics and plastic sources rather than the result of elevated habitat level concentration. Although not of a higher abundance in seagrass, such contamination in seagrass is of cause for concern given the high dependency of many species of fish on these habitat types and the potential for plastics to move up the food chain.

A review of plastic and microplastic pollution towards the Malaysian marine environment

“…A study found out that low-density MPs (PE, PP and PVC) ranging from 0.55 -287.00 mm in seagrasses (Posidonia oceanica) are capable of forming aggregates by using lignocellulosic fibers and carried to shore by wave action while high-density MPs will instantly sink to seagrass beds [96]. Additionally, [97] reported that lighter MP is less likely to be trapped in seagrass meadows compared to heavier ones because of the lower sinking rate in the water column, which allows it to not be easily trapped to seagrass blades by using biofilms. Gradual MP accumulation at seagrass meadows has also been reported to change sediment composition which may affect seagrass growth [95] and threaten the health of marine organisms living near the meadows with increasing MP exposures [94].…”

Microplastics in mangroves and coral reef ecosystems: a review

“…Marine canopies are formed underwater in this ecosystem by plants such as seagrass meadows, and they inhabit and provide shelter for a wide range of fishes and invertebrates (Unsworth et al 2021). The particle trapping ability of these canopies are dependent on the tidal patterns, and so, contamination in these areas may deposit particles within this megafauna.…”

An Assessment of Microplastics (MPs) Sedimentary Accumulation in Seagrass Meadows of Mare Island Conservation Area, North Maluku, Indonesia

“…These microplastic particles can be found ubiquitously throughout the world both in urban (Dehghani et al, 2017), salt marsh habitat (Weinstein et al, 2016;Li et al, 2020) and in the ocean environment such as coastal sediments (Claessens et a.,l 2011 ;Coppock et al, 2017;Bissen and Chawchai 2020;Bakir et al, 2020;Hosseini et al, 2020), seawater (Loughlin et a., 2021, Bakir et al, 2020Qi et al, 2020;Hosseini et al, 2020), as well as marine biota such as fish (James et al, 2020), clams (Piarulli and Airoldi 2020), echinodermata (Plee and Pomory 2020), crustracea (Bakir et a.,l 2020), and even in deep sea sediments (Van Cauwenberghe et al, 2013;Zhang et al, 2020 ;Barrett et al, 2020). In addition, these microplastics have also been identified in various important ecosystems in the coastal and sea environments such as mangroves (Mohamed Nor et al, 2014;Deng et al, 2020;Zuo et al, 2020), seagrass meadows (Dahl et al, 2021;Goss et al, 2018;Jones et al, 2020;Unsworth et al, 2021), and coral reefs (Jeyasanta et al, 2020). The extensive distribution in various important ecosystems is feared to have a negative impact both in terms of ecology and human health.…”

“…The small size allows it to be consumed by low-level fauna which subsequently through trophic transfer in the food web system can result in microplastic biomagnification from preycontaminated to the predators (Browne et al, 2010;Goss et al, 2018;Jones et al, 2020). Given the high dependence of many species of habitats, especially commercial important species is a special concern because of the risk of microplastics contamination for human as the highest trophic levels (Bonello et al, 2018;Jones et al, 2020;Unsworth et al, 2021).…”

“…Seagrass meadows are able to reduce current and waves so that it can reduce water flow and increase sedimentation of fine particles. In addition, the accumulation of microplastics in sediment is also influenced by the height of the seagrass canopy in trapping the microplastics on the larger leaves and when these seagrass leaves will die, they will be degraded with the remaining microplastics into sediments (Unsworth et al, 2021;Goss et al, 2018;Jones et al, 2020). This can indicate that seagrass meadows are able to act as a place for hoarding microplastic contamination (Jones et al, 2020).…”