Abstract
The Gulf of Mexico (GoM) is a dynamic marine ecosystem influenced by multiple natural and anthropogenic processes and inputs, such as the intrusion of warm oligotrophic water via the Loop Current, freshwater and nutrient input by the Mississippi River, and hydrocarbon inputs via natural seeps and industrial spills. Microbial plankton communities are important to pelagic food webs including in the GoM but understanding the drivers of the natural dynamics of these passively distributed microorganisms can be challenging in such a large and heterogeneous system. As part of the DEEPEND consortium, we applied high throughput 16S rRNA sequencing to investigate the spatial and temporal dynamics of pelagic microbial plankton related to several environmental conditions during two offshore cruises in 2015. Our results show dramatic community shifts across depths, especially between photic and aphotic zones. Though we only have two time points within a single year, observed temporal shifts in microbial plankton communities were restricted to the seasonally influenced epipelagic zone (0–200 m), and appear mainly driven by changes in temperature. Environmental selection in microbial plankton communities was depth-specific, with variables such as turbidity, salinity, and abundance of photosynthetic taxa strongly correlating with community structure in the epipelagic zone, while variables such as oxygen and specific nutrient concentrations were correlated with community structure at deeper depths.
Highlights
Understanding the ecology, taxonomy and distribution of diverse marine microorganisms remains a challenging yet important task
By applying high throughput 16S rRNA gene sequencing technologies and modern analytical methods we provide a profile of the “natural variability” envelope in microbial plankton communities of the offshore pelagic ecosystem
The pelagic environment in cruise DP02 (August 2015) was characterized by a strong Loop Current that protruded northward into the northern Gulf of Mexico (GoM) during the cruise, and a high outflow of the MS River (Figure 1 and Supplementary Figure S1). These two features collided during the DP02 cruise resulting in the transport of low salinity river water into the oceanic pelagic environment (Supplementary Table S1 and Supplementary Figure S1)
Summary
Understanding the ecology, taxonomy and distribution of diverse marine microorganisms (bacteria, fungi, protozoans, and viruses) remains a challenging yet important task. Variable mesoscale features powered by the Loop Current dominate upper level (0–1200 m) seawater dynamics in the GoM (Sturges et al, 1993; Welsh and Inoue, 2000; Hamilton and LugoFernandez, 2001) This feature can lead to the formation of persistent (weeks to months), anti-cyclonic, down-welling eddies composed of warm oligotrophic Caribbean water, leads to a high-degree of vertical mixing causing a well-oxygenated oxygen minimum zone, and may be an important driver of plankton and nekton dispersal as well as providing distinct pelagic habitat (Olson, 1991; Rabalais and Turner, 2001; Rivas et al, 2005; Paulmier and Ruiz-Pino, 2008; Sturges and Kenyon, 2008; Chang et al, 2011; Lindo-Atichati et al, 2012; Wells et al, 2017). Riverine input from the Mississippi River introduces massive amounts of fresh water laden with agricultural nutrient runoff and terrigenous sediment from the central United States (Rabalais and Turner, 2001; Mason et al, 2016)
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