Nanoscale Insights into the Impacts of Microplastics on Marine Phytoplankton

Abstract

Marine phytoplankton, vital to ocean food webs and global nutrient cycles, are increasingly threatened by microplastic (MP) pollution. However, the precise ways these tiny particles harm phytoplankton at the cellular level remain unclear. This thesis deciphers the nanoscale interactions between MPs and algal cells, combining cutting-edge microscopy, physiological measurement, and chemical characterization to reveal how MPs reshape phytoplankton health.

Primarily, we uncovered how different algal species respond uniquely to MP exposure. Algae with smooth cell walls developed deep dents, wrinkles, and even internalized MPs, which led to diverse surface deformities. In contrast, diatoms with porous silica shells trapped MPs within their intricate frustule structures, thus minimizing morphological damage. Atomic force microscopy (AFM) further confirmed that these algae lost nanostructural regularity and mechanical strength with species-specific disparities.

This thesis then explored how nutrient imbalance influences MP tolerance in phytoplankton via inducing nanoscale modifications to their cell surfaces. Under Si limitation, diatoms produced mechanically weaker, more adhesive, and more porous frustules. These cells showed inhibited growth, greater membrane damage, and were attached with more MPs. Surface potential and chemical composition analysis further linked this vulnerability to altered frustule properties, including reduced silicification and enhanced electrical attraction that facilitated MP adsorption.

Finally, this thesis investigated how emerging plastic pollutants like mask-released debris (MD) affect marine phytoplankton. MD not only inhibited diatom growth but also impaired their ecological functions. Under MD exposure, diatoms sank slower and less of them were consumed by copepods, which could disrupt carbon transfer within marine food chains. Nanoscale imaging tied these changes to rougher cell surfaces, reduced adhesion, higher modulus, and shifts in surface chemistry of the diatoms cultured with MD.

By connecting nanoscale damage to single-cell and population-level consequences, this work has revealed the multifaceted threats MPs pose to marine phytoplankton. The findings can help evaluate the adverse effects of plastic input on marine ecosystems and raise awareness of the nanoscale mechanisms involved.

Date of Award	2025
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Hongbin LIU (Supervisor) & Ke Pan (Supervisor)