Spatial variability overwhelms seasonal patterns in bacterioplankton communities across a river to ocean gradient

Abstract

Few studies of microbial biogeography address variability across both multiple habitats and multiple seasons. Here we examine the spatial and temporal variability of bacterioplankton community composition of the Columbia River coastal margin using 16S amplicon pyrosequencing of 300 water samples collected in 2007 and 2008. Communities separated into seven groups (ANOSIM, Po0.001): river, estuary, plume, epipelagic, mesopelagic, shelf bottom (deptho350 m) and slope bottom (depth4850 m). The ordination of these samples was correlated with salinity (q ¼ À0.83) and depth (q ¼ À0.62). Temporal patterns were obscured by spatial variability among the coastal environments, and could only be detected within individual groups. Thus, structuring environmental factors (for example, salinity, depth) dominate over seasonal changes in determining community composition. Seasonal variability was detected across an annual cycle in the river, estuary and plume where communities separated into two groups, early year (April-July) and late year (August-Nov), demonstrating annual reassembly of communities over time. Determining both the spatial and temporal variability of bacterioplankton communities provides a framework for modeling these communities across environmental gradients from river to deep ocean.

Deciphering associations between dissolved organic molecules and bacterial communities in a pelagic marine system

“…Hence, even if DNA-based BC composition is individually not significantly correlated with salinity (Supplementary Table S5), the canonical correlation to DOM molecular composition identifies the connection to terrestrial influence as an important driver of the North Sea. The presence of a general salinity gradient mirrored in the BC composition has been reported previously, for example, by Bouvier and del Giorgio (2002) and Fortunato et al (2012), who established salinity as the main driver of BC structure along a pronounced salinity gradient from river to ocean. In accordance to their findings, we hypothesize that the DOM compounds and the total BC that reach the North Sea undergo mixing and transformation processes from the coast toward the Atlantic on similar timescales of several months and thus retain the intermediate history of the water masses, the 'riverine legacy'.…”

Determining indicator taxa across spatial and seasonal gradients in the Columbia River coastal margin

“…DNA samples (1-6 l per sample) were collected from 10 l Niskin bottles, preserved and extracted as described previously (Fortunato and Crump, 2011), and PCR-amplified for amplicon pyrosequencing using primers targeting bacterial 16S rRNA genes (Hamady et al, 2008) as described previously (Fortunato et al, 2012). Pyrosequencing was completed in two runs at Engencore at the University of South Carolina (http:// engencore.sc.edu/).…”

“…An earlier study of 300 water samples collected in 2007 and 2008 showed bacterioplankton communities of the Columbia River coastal margin separated into seven environments: river, estuary, plume, epipelagic, mesopelagic, shelf bottom and slope bottom (Fortunato et al, 2012). Here we expand on this work and focus on population-level analyses to determine the key taxa in each environment and describe how the relative abundance of these taxa shifts with changing environmental conditions.…”

“…Biogeography of aquatic microbial communities has been well described across spatial and seasonal scales (Gilbert et al, 2009;Galand et al, 2010;Kirchman et al, 2010;Crump et al, 2012;Fortunato et al, 2012), and although most studies discuss changes in community composition and structure, little is known about the specific taxa that distinguish one community from another. In one long-term study of the English Channel, Gilbert et al (2012) showed strong repeatable seasonal patterns in the general bacterioplankton community and in specific taxonomic groups, and found that seasonal variability was influenced by length of day, temperature, nutrients, and photosynthetically active radiation, rather than biomass of zooplankton species.…”

“…Figure S1). Samples were collected using an instrumented 12-or 24-bottle rosette equipped with a Seabird 911 þ conductivity-temperature-depth sensor or a highvolume low-pressure pump as described previously (Fortunato et al, 2012).…”