Ecological implications of nanostructures and mechanical properties in marine phytoplankton

Abstract

The cell walls of phytoplankton often serve as a defense against predation in marine ecology, but there has been a lack of quantitative analysis of how their mechanical properties are affected by environmental changes and what their ecological implications are. This doctoral research thesis aims to use the advanced surface analysis technique, atomic force microscopy, to quantitatively analyze and study the mechanical properties of diatom cell walls under intracellular biogenic silica content, predator cues, silicon limitation, and coccolithophores under ocean acidification. Our results reveal that (1) The nanostructure and chemical composition of diatom frustules determine the mechanical strength of diatom frustules, not solely the biogenic silica content. Copepods prefer diatoms with low mechanical strength rather than low biogenic silica content. (2) Diatoms exposed to copepod cues have high growth rates and high mechanical performance, which may be related to the increase in condensed silicon content on the diatom frustule surface. (3) Silicon limitation alters the chemical composition of the diatom frustule surface and greatly reduces the mechanical properties of diatoms, leading to an increase in copepod predation. (4) The calcification ability of coccoliths on the coccolithophore surface is impaired under ocean acidification, and nanoscale defects appear on the surface, leading to a decrease in their mechanical properties and an increase in copepod predation. These findings enhance our understanding of the function of phytoplankton cell walls in ecosystems and provide guidance for further understanding the marine planktonic food web.

Date of Award	2023
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Hongbin LIU (Supervisor) & Ke Pan (Supervisor)