Abstract
Vibrio is a cosmopolitan genus of marine bacteria, highly investigated in coastal and estuarine environments. Vibrio have also been isolated from pelagic waters, yet very little is known about the ecology of these oligotrophic species. In this study we examined the relative change in bacterial abundance and more specifically the dynamics of Vibrio in the tropical North Atlantic in response to the arrival of pulses of Saharan dust aerosols, a major source of biologically important nutrients for downwind marine surface waters. Aerosol and surface water samples were collected over one month coinciding with at least two distinct dust events. Total bacterial counts increased by 1.6-fold correlating with the arrival of Saharan dust (r=0.76; p=0.001). Virus-like particles also followed this trend and were correlated with bacterial counts (r=0.67; p=0.01). Vibrio specific qPCR targeting the 16S rRNA gene ranged from below detection limits to a high of 9,145 gene copies ml-1 with the arrival of dust. This increase equated to 6.5 x 10^2 – 1.5 x 10^3 individual genome equivalents ml-1 based on the known range of 16S rRNA copies among this genus. Vibrio exhibited bloom-bust cycles potentially attributed to selective viral lysis or bloom depletion of organic carbon. This work is one of the few studies to examine the open ocean ecology of Vibrio, a conditionally rare taxon, whose bloom-bust lifestyle likely is a contributing factor in the flow of nutrients and energy in pelagic ecosystems.
Highlights
The pelagic ocean is one of the largest habitats on earth
Aerosol particle counts were used as a proxy for the presence of Saharan dust particulate matter in the immediate vicinity of sampling when Navy Aerosol Analysis and Prediction System (NAAPS) modeled data indicated Saharan aerosols in the region
The high dust load during these dates was confirmed by NAAPS surface level modeling with a peak dust level in the region indicated on 14–15 October and 23 October (∼80 μg m−3) (Figure 3)
Summary
The pelagic ocean is one of the largest habitats on earth. Surface water microbes in the ocean drive the majority of biogeochemical cycling and are a critical linkage in the ocean-atmosphere exchange of gases that affect global climate (Falkowski et al, 2008). An opposing adaptive strategy is characterized by the rare opportunistic group, with greater genomic and metabolic diversity, able to survive in low Vibrio Populations in Mid-Atlantic Surface Waters numbers, but capable of rapidly exploiting spatially and temporally variable nutrient resources, occasionally becoming highly abundant in the community (Yooseph et al, 2010) This latter group of conditionally rare taxa can have a disproportionate effect on ecosystem functioning during periodic bloom conditions by providing important ecosystem services that are disproportionate to their initial low abundance (Shade et al, 2014). Because of their rarity in ocean surveys, little is known about conditionally rare taxa and what environmental drivers induce an increase in their abundance, especially in remote pelagic systems
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