The diversity and functioning of coastal microbial communities

Microbial communities are notably complex and underpin many important global biogeochemical processes. However, there is still much that we do not know regarding the structuring dynamics of microbial communities and their biodiversity-ecosystem functioning (BEF) relationships. Therefore, there is great importance in researching these aspects in greater detail. In order to do this kind of analysis, large datasets are needed to properly capture the nuances of microbial communities. The CBESS (Coastal Biodiversity and Ecosystem Service Sustainability) dataset used here is one such dataset. Random forest analysis, a type of machine learning, was applied here to an expansive dataset of microbial metabarcode reads and environmental measures across multiple spatial scales. Two different coastal habitats were used to create further distinctions. Random forest models were created with and without environmental measures and it was found that notable differences across domain, spatial scale, and habitat were only observed when environmental measures were included. The relative importance of environmental factors increased both when scale increased and when specific habitat models were constructed, emphasizing the role that scale and context play in the interpretation of this type of analysis. Across domains, the relative importance of taxonomic factors was much higher in bacteria, indicating a possible increased role of dispersal limitations for that domain. Co-occurrence networks were then constructed using the same dataset to investigate if there were any relationships between microbial network structure and process profiles across spatial scales. Significant relationships were only found at the smallest spatial scale with bacteria and archaea exhibiting nearly all the relationships. In those two domains, clear ecological patterns were linked with specific ecological processes for both network size and network interconnectedness. Across taxonomic levels, bacteria had stronger links at higher taxonomic levels and archaea had the strongest links at the genus level. Overall, this study reveals both the complex spatial dynamics of microbial community structuring and BEF relationships that exist between microbial communities and globally important processes.