Abstract
Despite nutrient-depleted conditions, coral reef waters harbor abundant and diverse microbes; as major agents of microbial mortality, viruses are likely to influence microbial processes in these ecosystems. However, little is known about marine viruses in these rapidly changing ecosystems. Here we examined spatial and short-term temporal variability in marine viral abundance (VA) and viral lytic activity across various reef habitats surrounding Moorea Island (French Polynesia) in the South Pacific. Water samples were collected along four regional cross-reef transects and during a time-series in Opunohu Bay. Results revealed high VA (range: 5.6 × 106–3.6 × 107 viruses ml-1) and lytic viral production (range: 1.5 × 109–9.2 × 1010 viruses l-1 d-1). Flow cytometry revealed that viral assemblages were composed of three subsets that each displayed distinct spatiotemporal relationships with nutrient concentrations and autotrophic and heterotrophic microbial abundances. The results highlight dynamic shifts in viral community structure and imply that each of these three subsets is ecologically important and likely to infect distinct microbial hosts in reef waters. Based on viral-reduction approach, we estimate that lytic viruses were responsible for the removal of ca. 24–367% of bacterial standing stock d-1 and the release of ca. 1.0–62 μg of organic carbon l-1 d-1 in reef waters. Overall, this work demonstrates the highly dynamic distribution of viruses and their critical roles in controlling microbial mortality and nutrient cycling in coral reef water ecosystems.
Highlights
Viruses are increasingly recognized as the most abundant and dynamic biological entities in marine ecosystems
The results show high spatial heterogeneity and relatively low temporal changes in viral abundance (VA) and lytic activity, concomitant with shifts in microbial host population dynamics
No significant differences in nutrient concentrations were detected among reef habitats, dissolved inorganic nitrogen (DIN) concentrations were higher in the FRG (0.48 ± 0.14 μM) relative to the LAG (0.40 ± 0.13 μM) and back reef (BR) (0.38 ± 0.09 μM), CR (0.34 ± 0.09 μM), and fore reef (FOR) (0.41 ± 0.10 μM; KW, p > 0.05)
Summary
Viruses are increasingly recognized as the most abundant and dynamic biological entities in marine ecosystems (e.g., reviewed in Fuhrman, 1999; Wommack and Colwell, 2000; Weinbauer, 2004; Suttle, 2007). The release of organic cellular content and nutrients upon viral lysis can stimulate autotrophic and heterotrophic microbial activity (Gobler et al, 1997; Middelboe and Lyck, 2002; Weinbauer et al, 2011; Shelford et al, 2012) and increase diversity (Weinbauer and Rassoulzadegan, 2004; Motegi et al, 2013), with major effects on global biogeochemical cycles and flow of energy in the oceans (Fuhrman, 1999; Wilhelm and Suttle, 1999; Suttle, 2007). Despite their critical impact in the oceans, there is still a lack of data on the spatial and temporal dynamics of viruses and their ecological influence in marine microbial communities. In this setting of nutrient poor conditions and high microbial abundance, viruses may play a important ecological role in shaping microbial communities, with potential impacts on carbon cycling and energy transfer to higher trophic levels
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