Abstract
Temperate coastal marine environments are replete with complex biotic and abiotic interactions that are amplified during spring and summer phytoplankton blooms. During these events, heterotrophic bacterioplankton respond to successional releases of dissolved organic matter as algal cells are lysed. Annual seasonal shifts in the community composition of free-living bacterioplankton follow broadly predictable patterns, but whether similar communities respond each year to bloom disturbance events remains unknown owing to a lack of data sets, employing high-frequency sampling over multiple years. We capture the fine-scale microdiversity of these events with weekly sampling using a high-resolution method to discriminate 16S ribosomal RNA gene amplicons that are >99% identical. Furthermore, we used 2 complete years of data to facilitate identification of recurrent sub-networks of co-varying microbes. We demonstrate that despite inter-annual variation in phytoplankton blooms and despite the dynamism of a coastal–oceanic transition zone, patterns of microdiversity are recurrent during both bloom and non-bloom conditions. Sub-networks of co-occurring microbes identified reveal that correlation structures between community members appear quite stable in a seasonally driven response to oligotrophic and eutrophic conditions.
Highlights
Microbes in coastal marine environments are influenced by multiple biotic and abiotic elements that mediate relationships between community members
Overall diatoms tend to dominate the climax of spring and summer blooms, with the exception of marine raphidophyte Chattonella, which conspicuously replaces diatoms in the Detection of seasonally structured modules
Using each of the module eigengenes (MEs) from 2011 and 2012, we performed a redundancy analysis (RDA) to extract variation in the MEs that could be explained by the measured physicochemical variables
Summary
Microbes in coastal marine environments are influenced by multiple biotic and abiotic elements that mediate relationships between community members. Shifts in community structure can be modulated by changes in bottom-up substrate availability induced by seasonal forcing such as solar angle and upwelling and by top–down predator–prey interactions (reviewed in Fuhrman et al, 2015) These dynamics are amplified in temperate coastal marine zones when phytoplankton form massive blooms each spring and summer. Algae release a complex array of dissolved organic matter These organic substrates are almost exclusively accessible by Biodiversity studies at long-term sampling stations have revealed broadly recurrent patterns within marine planktonic communities (Steinberg et al, 2001; Gilbert et al, 2012; Chow et al, 2013; Fuhrman et al, 2015).
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