Viral lysis and microzooplankton grazing of phytoplankton throughout the Southern Ocean

Evans, Claire; Brussaard, Corina P. D.

doi:10.4319/lo.2012.57.6.1826

Cited by 34 publications

(34 citation statements)

References 37 publications

(89 reference statements)

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“…Although this observation might be a local or seasonal phenomenon, our findings are consistent with a smaller-scale study in the North Sea , which reported low viral lysis rates of picophytoplankton in offshore waters above 55°N. Furthermore, data from the Southern Ocean point at low viral lysis rates of phytoplankton over a relatively broad geographic range from at least 43°S to 70°S on the southern hemisphere (Evans and Brussaard, 2012). This suggests that low viral lysis rates at higher latitudes are not unique for our data set, but may represent a global pattern.…”

Section: Discussionsupporting

confidence: 80%

“…Estimates of viral lysis rates of natural phytoplankton populations remain scarce, and consequently the importance of viruses in comparison with other loss factors remains unclear. Rates of viral-mediated mortality for Synechococcus (that is, 0.03-0.49 per day), picoeukaryotic phytoplankton (that is, 0-0.81 per day) and nanoeukaryotic phytoplankton (that is, 0-1.05 per day) were comparable to the ranges reported in the literature (Baudoux et al, 2007Evans and Brussaard, 2012;Tsai et al, 2012). The viral lysis rates of Prochlorococcus (that is, 0.02-0.57 per day) presented here were higher than the maximal 0.06 per day reported thus far (Baudoux et al, 2007).…”

Section: Discussionsupporting

confidence: 73%

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Latitudinal variation in virus-induced mortality of phytoplankton across the North Atlantic Ocean

et al. 2015

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Viral lysis of phytoplankton constrains marine primary production, food web dynamics and biogeochemical cycles in the ocean. Yet, little is known about the biogeographical distribution of viral lysis rates across the global ocean. To address this, we investigated phytoplankton groupspecific viral lysis rates along a latitudinal gradient within the North Atlantic Ocean. The data show large-scale distribution patterns of different virus groups across the North Atlantic that are associated with the biogeographical distributions of their potential microbial hosts. Average virusmediated lysis rates of the picocyanobacteria Prochlorococcus and Synechococcus were lower than those of the picoeukaryotic and nanoeukaryotic phytoplankton (that is, 0.14 per day compared with 0.19 and 0.23 per day, respectively). Total phytoplankton mortality (virus plus grazer-mediated) was comparable to the gross growth rate, demonstrating high turnover rates of phytoplankton populations. Virus-induced mortality was an important loss process at low and mid latitudes, whereas phytoplankton mortality was dominated by microzooplankton grazing at higher latitudes (456°N). This shift from a viral-lysis-dominated to a grazing-dominated phytoplankton community was associated with a decrease in temperature and salinity, and the decrease in viral lysis rates was also associated with increased vertical mixing at higher latitudes. Ocean-climate models predict that surface warming will lead to an expansion of the stratified and oligotrophic regions of the world's oceans. Our findings suggest that these future shifts in the regional climate of the ocean surface layer are likely to increase the contribution of viral lysis to phytoplankton mortality in the higher-latitude waters of the North Atlantic, which may potentially reduce transfer of matter and energy up the food chain and thus affect the capacity of the northern North Atlantic to act as a long-term sink for CO 2 .

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Section: Discussionsupporting

confidence: 80%

Section: Discussionsupporting

confidence: 73%

Latitudinal variation in virus-induced mortality of phytoplankton across the North Atlantic Ocean

et al. 2015

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“…However, while mixed‐layer stocks of new iron appear more akin to a static inventory with little day‐to‐day change in their magnitude [ Croot et al , ], that from the recycled iron inventory is more dynamic as it is being “heavily trafficked” [ Morel and Price , ; Nuester et al , ] and hence shuttled around on timescales of hours [ Poorvin et al , ; Strzepek et al , ]. The timescales of iron recycling are inextricably linked to the turnover times of much of the microbial and planktonic populations, as the main modes of recycling involve grazing and viral lysis [ Boyd et al , ; Evans and Brussard , ; Matteson et al , ]. Based on the partitioning of biotic iron, much of this total biotic iron pool is associated with these small, rapidly turned over cells and/or their grazers (Figure B).…”

Section: Resultsmentioning

confidence: 99%

Why are biotic iron pools uniform across high‐ and low‐iron pelagic ecosystems?

Boyd

Strzepek

Ellwood

et al. 2015

Global Biogeochemical Cycles

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Dissolved iron supply is pivotal in setting global phytoplankton productivity and pelagic ecosystem structure. However, most studies of the role of iron have focussed on carbon biogeochemistry within pelagic ecosystems, with less effort to quantify the iron biogeochemical cycle. Here we compare mixed-layer biotic iron inventories from a low-iron (~0.06 nmol L À1 ) subantarctic (FeCycle study) and a seasonally high-iron (~0.6 nmol L À1 ) subtropical (FeCycle II study) site. Both studies were quasi-Lagrangian, and had multi-day occupation, common sampling protocols, and indirect estimates of biotic iron (from a limited range of available published biovolume/carbon/iron quotas). Biotic iron pools were comparable (~100 ± 30 pmol L À1) for low-and high-iron waters, despite a tenfold difference in dissolved iron concentrations. Consistency in biotic iron inventories (~80 ± 24 pmol L À1, largely estimated using a limited range of available quotas) was also conspicuous for three Southern Ocean polar sites. Insights into the extent to which uniformity in biotic iron inventories was driven by the need to apply common iron quotas obtained from laboratory cultures were provided from FeCycle II. The observed twofold to threefold range of iron quotas during the evolution of FeCycle II subtropical bloom was much less than reported from laboratory monocultures. Furthermore, the iron recycling efficiency varied by fourfold during FeCycle II, increasing as stocks of new iron were depleted, suggesting that quotas and iron recycling efficiencies together set biotic iron pools. Hence, site-specific differences in iron recycling efficiencies (which provide 20-50% and 90% of total iron supply in high-and low-iron waters, respectively) help offset the differences in new iron inputs between low-and high-iron sites. Future parameterization of iron in biogeochemical models must focus on the drivers of biotic iron inventories, including the differing iron requirements of the resident biota, and the subsequent fate (retention/export/recycling) of the biotic iron.

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“…Our present understanding of phytoplankton diversity and productivity in the WG, and Southern Ocean in general, is based upon bottom‐up rather than top‐down processes, in spite of the importance of grazing in the polar carbon cycle (le Quéré et al, ; Smetacek et al, ). Field experiments indicate that viral lysis of phytoplankton (both picoplankton and nanoplankton) can be relatively minor in the WG, while grazing by microzooplankton exerts significant control of phytoplankton growth (Agustí & Duarte, ; Evans & Brussaard, ; Froneman & Perissinotto, ; Henjes et al, ; Jacobsen et al, ). In contrast, larger zooplankton are of secondary relevance in controlling phytoplankton biomass (Garcia et al, ).…”

Section: Biology I: Phytoplankton Of the Wgmentioning

confidence: 99%

The Weddell Gyre, Southern Ocean: Present Knowledge and Future Challenges

Vernet

Geibert

Hoppema

et al. 2019

Reviews of Geophysics

154

147

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The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures, and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide, and global modeling efforts—thereby enhancing predictions of the WG in global ocean circulation and climate.

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Viral lysis and microzooplankton grazing of phytoplankton throughout the Southern Ocean

Abstract: We investigated microzooplankton grazing and viral lysis of the pico-and nanophytoplankton community in

Cited by 34 publications

References 37 publications

Latitudinal variation in virus-induced mortality of phytoplankton across the North Atlantic Ocean

Latitudinal variation in virus-induced mortality of phytoplankton across the North Atlantic Ocean

Why are biotic iron pools uniform across high‐ and low‐iron pelagic ecosystems?

The Weddell Gyre, Southern Ocean: Present Knowledge and Future Challenges

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