Assessing the effects of microplastics on marine benthic communities

Project Rationale:

Continental shelf sediments are biogeochemical hotspots. Interactions between benthic invertebrates and bacteria drive the remineralization of organic matter, returning inorganic nutrients to the overlying waters and stimulating primary production. This ultimately sustains the production of harvestable fish and shellfish biomass.

Recent modelling studies suggest that shelf sediments will receive the majority of marine microplastics (MPs). There is growing concern that these non-degradable particulate contaminants have the potential to directly harm marine animals. Little is known about the direct effects of MPs and their constituent additives and adsorbed chemicals on the benthic microorganisms that drive the biogeochemistry of marine sediments. This hinders our ability to understand how marine ecosystems, and the many functions and services they provide, are likely to respond to the projected increase in MPs in the coming decades.

This PhD will investigate how MPs and their associated contaminants (e.g. the ubiquitous, lipophilic pesticide DDT) influence the composition of sediment microorganisms and their capacity to remineralise organic matter. Additional experiments will examine how the presence of benthic invertebrates, and their behavioral responses to MPs, influence sediment microbial communities and the rates at which they recycle nutrients.

Methodology:

Incubation experiments will be used to examine if the presence of MPs at the seafloor influences the composition of the resident microbial community and its metabolic potential. Additional experiments will determine if the effects of MPs increase when organic contaminants, such as DDT, are adsorbed to their surface. Bacterial phospholipid fatty acids (PLFAs) from the incubated sediments will be extracted, identified and quantified to assess changes in the bacterial community composition (Mayor et al., 2013, 2017). Changes in the stable isotope (12C/13C) signatures of individual PLFAs will be used to identify if/when the underlying metabolic pathways are being affected. Experiments will also assess how MPs influence the burrowing and irrigation behaviour of functionally important invertebrates, and the associated effects on benthic microbes and their capacity for nutrient cycling (Godbold & Solan 2013). We encourage the student to build on the proposed work and extend it into an area of their own innovation. Possible ideas include: i) combining the PLFA-based work with other molecular tools, e.g. genomics, transcriptomics, metabolomics, ii) using process-based models to explore the biogeochemical implications of the resulting data at a wider scale e.g. Western European Shelf.

Training:

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre. Specific training will include:

• Statistics-focused experimental design.
• Conducting multi-factorial benthic incubation experiments.
• Making biogeochemical process rate measurements, e.g. consumption of O2, production of CO2, NH4, NO3, PO4.
• Compound-specific stable isotope analysis using gas chromatography combustion isotope ratio mass spectrometry.
• Quantification of faunal burrowing behaviour using fluorescent sediment profile imaging.
• Multivariate statistical analysis in the R programming language.
• There is strong potential for the student to participate on one or more research cruise during their PhD.