Where does the plastic go? Microplastic loading in seagrass vs mangroves

Description

Plastic pollution from anthropogenic activities on land and sea is a ubiquitous global issue, contributing >80% of marine litter. Over time, plastic disintegrates into increasingly smaller pieces (microplastics <5 mm) by physical abrasion from wave action, photodegradation or biological processes. These less conspicuous microplastics are transported through pelagic and benthic zones, dependent upon their density and biofouling. They consist of fibres, fragments and particles, which sorb multiple toxic contaminants posing a risk to incidental consumers. Microplastics have now been found in every aquatic ecosystem, including mangroves and seagrass habitats. These ecologically and economically important ecosystems act as filters helping to keep coastal zones healthy and play important roles in blue carbon storage. Mangroves, also important habitats for fish and shellfish, link land to sea and are susceptible to accumulating plastic litter from both urban sources and oceanic deposition.

Impact

Microplastics have been identified in all aquatic ecosystems, including mangrove and seagrass habitats, which are often called the kidneys of the Great Barrier Reef because they act as land-to-sea buffers by filtering out particulate matter and contaminants. As such, they could play a beneficial role in trapping microplastics and reducing the flux to offshore habitats like the Great Barrier Reef. This would be the first known study to investigate the role of mangroves and seagrass beds as a protective barrier to further limit the dispersal of microplastics to the GBR. However, these benefits likely incur a presently unknown cost to mangroves and seagrasses, and the animals that depend on them.

Mangroves act as a natural repository for litter from both land and oceanic sources however, they may also play a role in plastic biodegradation. To date, no studies have determined whether fragmented plastics are retained in mangrove soils or redispersed to adjacent habitats (such as seagrass) with tidal flushing. This will be the first study to identify the mechanisms involved in this process and to examine flushing rates based on simulated tidal regimes, turbulence and storm water fluxes and transportation likelihood to seagrass beds. Adhesion of microplastics to seagrass blades and roots could impact productivity (impacts in freshwater plants include photosynthetic inhibition, reduced growth and chlorophyll concentrations). This study will investigate the physiological impacts of microplastic contamination in seagrass beds.

Acknowledgement of funding:

This project has received funding support from CQUniversity New Staff Grants scheme