Are Biofilm and Dimethyl Sulfide Facilitators for Microplastic Ingestion in Filter Feeders?
- Siu Gin CHEUNG (Principal Investigator / Project Coordinator)Department of Chemistry
- Jill Man Ying CHIU (Co-Investigator)
- Chun Yuen Alex WONG (Co-Investigator)Department of Chemistry
DescriptionOur society is addicted to plastic. We generate around 300 million tons of plastic waste every year, with more than 8 million tons dumped into the oceans. It is estimated that 5 trillion pieces of plastic waste occur in the world’s oceans and affect more than 800 marine animal species. Microplastics (MPs), plastic pieces with a diameter of < 5 mm, can be produced for specific purposes or generated from the degradation of larger plastic pieces. Owing to the small size of MPs, they are ingested by various marine organisms and exert harmful effects such as inflammation and reduction in energy intake. Considering their hydrophobicity and large surface area to volume ratio, MPs provide an excellent platform for the adsorption of persistent organic pollutants in the ocean, such as polychlorinated biphenyls and polycyclic aromatic hydrocarbons, as well as pathogenic bacteria and viruses. These pollutants and microorganisms may threaten the health of marine organisms through MP ingestion. MPs released in the ocean are attached by organic materials, which facilitate the colonization and development of microbial communities. The secretion of extracellular polymeric substances (EPS) by the microbes modifies the surface properties of MPs and provides a stable environment for the microbial community. The biofilm on MPs undergoes successional changes, with bacteria and viruses as pioneers and followed by phytoplankton (e.g., diatoms and dinoflagellates) in the latter part of the biofilm development. Dimethylsulfoniopropionate (DMSP) is produced by marine phytoplankton for osmoregulation, defense, and cryoprotection. Through bacterial degradation or zooplankton grazing, DMSP is converted into dimethyl sulfide (DMS). Foragers, such as seabirds and fish rely on DMSP/DMS as cues in localizing prey. Since phytoplankton occurs on the biofilm of MPs, the release of DMSP/DMS from MPs will confuse marine foragers, which mistakenly consider MPs as food. Nevertheless, MPs coated with biofilm can be a source of energy as biofilm consists of living cells and organic substances such as polysaccharides, proteins, and lipids. Filter feeders (e.g., mussels, barnacles, and sea squirts) collect suspended particles in water as food. They play a significant role in the cycling of nutrients in the ecosystem. Barnacles and mussels also enhance habitat complexity by creating 3-dimensional structures. In benthic habitats where these filter-feeders thrive, sediment resuspension reduces food quality as inorganic matter mixes with organic particles. To enhance energy intake, mussels and sea squirts can select nutritious particles for ingestion. Particles are sorted based on properties such as size, wettability, hydrophobicity, and texture. In contrast, barnacles are non-selective feeders without particle sorting capability. This study will clarify the role of biofilm and DMS in facilitating particle selection in selective feeding mussels and sea squirts compared to non-selective feeding barnacles. MPs incubated with biofilm at different stages of development or infused with varying concentrations of DMS will be used in the experiments. The experiment will be repeated for two forms (microsphere, microfiber) and sizes of MPs, as these characteristics are known to affect particle selectivity in filter feeders. Many laboratory studies on the effects of MPs in marine organisms have used virgin MPs without biofilm. If biofilm can enhance MP ingestion, studies using virgin MPs will underestimate the biological impact of MPs on selective filter feeders. Furthermore, an understanding of the energy value of the biofilm can provide a more realistic assessment of the impact of microplastics on the nutrition of filter feeders. Determining the temporal and spatial variations in the microplastics and their associated biofilm in the local marine environment will further enhance our understanding of the ecological impact of microplastics.
|Effective start/end date||1/01/23 → …|