Abstract
Marine biofilms are found in association with suspended particles, surfaces of the marine benthos, and on manmade structures. Biofilms support bacterial diversity and interactions including cooperative and antagonistic processes between community members but have negative impacts via biofouling and microbially influenced corrosion. We sought to identify major microbial contributors to the nascent biofilm community in Spring, Summer, and Fall in the temperate, coastal Northwestern Atlantic, to elucidate environmental factors contributing to any differences, and to quantify influences of deterministic and stochastic processes to community assembly. Alpha diversity in biofilms generally increased over the week-long deployment with a significant effect of surface type seen in the Spring and Summer. Beta diversity showed strong seasonality and the communities were most distinct at the earliest colonization stage but began to converge as the biofilms aged, demonstrating a core biofilm community forms regardless of season. Alpha- and Gammaproteobacteria and Bacteroidia were consistently among the most abundant phyla, but finer taxonomic resolution revealed significant community turnover between seasons, correlating with shifting environmental conditions. All biofilms experienced deterministic community assembly with mean nearest taxon index (NTI) values >2 or < -2, but only Fall had higher than expected phylogenetic turnover between sampling dates (mean βNTI > 2), characteristic of variable selection. Spring and Summer demonstrated phylogenetic clustering as a result of primarily deterministic factors regulating community assembly. Conversely, Fall biofilms showed highly deterministic phylogenetic overdispersal governed by changes in the environment including declining temperature and concentrations of ammonium, nitrate, silica, chlorophyll a suggesting consistent selective pressure. These results provide fundamental information about microbial community dynamics in the marine environment and reveal processes and taxa that could serve in future efforts to combat biofouling and microbially influenced corrosion in marine industries.