MAPPING THE ‘PARTICLESCAPE’: DIVERSITY AND ACTIVITY OF MICROBIAL COMMUNITIES ASSOCIATED WITH PARTICLES IN THE MARINE ENVIRONMENT.

Particles are hotspots for marine microbial communities and impact ecosystem functioning, including the biological carbon pump. Although particle microbiomes differ across particle composition, type, size, source, and life history, this heterogeneity is often overlooked by using bulk-scale sampling approaches. In addition, knowledge of microbial eukaryotes in particle microbiomes is limited. I broadly set out to investigate how particle associated communities are structured at the macro and micro-scale which may have implications for wider food web interactions and biogeochemical cycling. In independent research chapters, I examined the diversity of bacteria (chapter 1) and activity of microbial eukaryotes associated with organic material (chapter 2 and 3) which play a role in marine carbon cycling and explored potential mechanisms structuring diversity dynamics observed. Here I discuss work done using both model and natural particles, including at the single particle level, combined with DNA and RNA amplicon sequencing of particle microbiomes in the North East Atlantic, Southern Ocean and Western English Channel. I show how particle source, life history and heterogeneity influences particle microbiomes across the whole water column (chapter 1) and reveal the diversity and activity of microbial eukaryotes (chapter 2) including fungi (chapter 3) associated with particles, the biological carbon pump and wider carbon cycling in the marine environment. This includes describing the identity and activity of microbial communities on particles across varying scales of complexity and incorporation of variability. I also add to the growing pool of knowledge of marine microbial communities in the understudied mesopelagic and bathypelagic. By exploring the particlescape, this work adds to the developing paradigm that particle microbiomes including microbial eukaryotes and particle-scale processes shaped by heterogeneity should be considered when understanding large-scale biogeochemical processes