Insensitivity of diverse and temporally variable particle-associated microbial communities to bulk seawater environmental parameters

Abstract

There is a growing recognition of the roles of marine microenvironments as reservoirs of biodiversity and as sites of enhanced biological activity and in facilitating biological interactions. Here, we examine the bacterial community inhabiting free-living and particle-associated seawater microenvironments at the Pivers Island Coastal Observatory (PICO). 16S rRNA gene libraries from monthly samples (July 2013 to August 2014) were used to identify microbes in seawater in four size fractions: > 63 μm (zooplankton and large particles), 63 to 5 μm(particles), 5 to 1 μm(small particles/dividing cells), and < 1 μm(free-living prokaryotes). Analyses of microbial community composition highlight the importance of the microhabitat (e.g., particle-associated versus free-living lifestyle) as communities cluster by size fraction, and the microhabitat explains more of the community variability than measured environmental parameters, including pH, particle concentration, projected daily insolation, nutrients, and temperature. While temperature is statistically associated with community changes in the < 1-μmand 5- to 1-μmfractions, none of the measured bulk seawater environmental variables are statistically significant in the larger-particle-associated fractions. These results, combined with high particle-associated community variability, especially in the largest size fraction (i.e., > 63 μm), suggest that particle composition, including eukaryotes and their associated microbiomes, may be an important factor in selecting for specific particle-associated bacteria.