scholarly journals Viral lysis modifies seasonal phytoplankton dynamics and carbon flow in the Southern Ocean

2021 ◽  
Author(s):  
Tristan E. G. Biggs ◽  
Jef Huisman ◽  
Corina P. D. Brussaard
Keyword(s):  
Microbial Community ◽  
Southern Ocean ◽  
Temporal Dynamics ◽  
Ecological Impact ◽  
Carbon Flow ◽  
Trophic Levels ◽  
Viral Lysis ◽  
Carbon Export ◽  
Community Interactions ◽  
Phytoplankton Communities

AbstractPhytoplankton form the base of marine food webs and are a primary means for carbon export in the Southern Ocean, a key area for global pCO2 drawdown. Viral lysis and grazing have very different effects on microbial community dynamics and carbon export, yet, very little is known about the relative magnitude and ecological impact of viral lysis on natural phytoplankton communities, especially in Antarctic waters. Here, we report on the temporal dynamics and relative importance of viral lysis rates, in comparison to grazing, for Antarctic nano- and pico-sized phytoplankton of varied taxonomy and size over a full productive season. Our results show that viral lysis was a major loss factor throughout the season, responsible for roughly half (58%) of seasonal phytoplankton carbon losses. Viral lysis appeared critically important for explaining temporal dynamics and for obtaining a complete seasonal mass balance of Antarctic phytoplankton. Group-specific responses indicated a negative correlation between grazing and viral losses in Phaeocystis and picoeukaryotes, while for other phytoplankton groups losses were more evenly spread throughout the season. Cryptophyte mortality was dominated by viral lysis, whereas small diatoms were mostly grazed. Larger diatoms dominated algal carbon flow and a single ‘lysis event’ directed >100% of daily carbon production away from higher trophic levels. This study highlights the need to consider viral lysis of key Antarctic phytoplankton for a better understanding of microbial community interactions and more accurate predictions of organic matter flux in this climate-sensitive region.

scholarly journals Polar opposites; bacterioplankton susceptibility and mycoplankton resistance to ocean acidification

2020 ◽  
Author(s):  
Storme Zaviar de Scally ◽  
Samuel Chaffron ◽  
Thulani Peter Makhalanyane
Keyword(s):  
Community Structure ◽  
Microbial Community ◽  
Southern Ocean ◽  
Ocean Acidification ◽  
Microbial Communities ◽  
Enzyme Activities ◽  
Experimental Manipulation ◽  
Trophic Levels ◽  
Community Interactions ◽  
Nitrogen Acquisition

ABSTRACTMicroorganisms form the basis of ocean ecosystems yet the effects of perturbations such as decreasing pH on microbial community structure, interactions and functionality remain compared to multicellular organisms. Using an experimental manipulation of Southern Ocean seawater, we subjected bacterioplankton and mycoplankton to artificial pH decreases, which are predicted to occur in the future. We show that acidification led to substantial increases of bacterioplankton diversity, while in contrast it had no effect on mycoplankton diversity. Our analyses revealed a loss of putative keystone taxa and a decrease in predicted community interactions as a response to lower pH levels. Bacterioplankton shifted from generalist to specialist community members, suggesting a specific stress response to unfavourable conditions. In addition, enzyme activities involved in nitrogen acquisition were lower at reduced pH levels, suggesting altered organic matter cycling in a more acidic ocean. Our findings suggest that bacterioplankton and mycoplankton may respond differentially to future ocean acidification, with potentially negative impacts on community structure and biogeochemical cycling in the Southern Ocean.IMPORTANCEOceans absorb the majority of anthropogenically produced CO2, the consequence of which is ocean acidification, a phenomenon already negatively impacting key marine organisms. Marine microbial communities form the basis of ocean food webs by generating nutrients for higher trophic levels, yet the response of these key microbial drivers to acidification remains unclear. This knowledge deficit is particularly true for understudied marine ecosystems such as the Southern Ocean. Using a mesocosm approach, we found that acidification severely impacts microbial community stability, by altering bacterioplankton community structure, reducing network complexity, and augmenting enzyme activities associated with nitrogen acquisition. This study adds to our understanding of the effects of ocean acidification on microbial communities, particularly within an environment expected to be largely effected by future anthropogenically driven climate change.

scholarly journals Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

2015 ◽  
Vol 12 (13) ◽  
pp. 3953-3971 ◽  
Author(s):  
S. Z. Rosengard ◽  
P. J. Lam ◽  
W. M. Balch ◽  
M. E. Auro ◽  
S. Pike ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Deep Ocean ◽  
Euphotic Zone ◽  
Biological Pump ◽  
Carbon Export ◽  
Mesopelagic Zone ◽  
Poc Flux ◽  
Phytoplankton Communities ◽  
Poc Export ◽  
Particulate Inorganic Carbon

Abstract. Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize, and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of > 51 μm POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition, and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-rich communities produce large and labile POC aggregates, which not only generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

scholarly journals Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

2015 ◽  
Vol 12 (3) ◽  
pp. 2843-2896
Author(s):  
S. Z. Rosengard ◽  
P. J. Lam ◽  
W. M. Balch ◽  
M. E. Auro ◽  
S. Pike ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Deep Ocean ◽  
Euphotic Zone ◽  
Biological Pump ◽  
Carbon Export ◽  
Mesopelagic Zone ◽  
Poc Flux ◽  
Phytoplankton Communities ◽  
Poc Export ◽  
Particulate Inorganic Carbon

Abstract. Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of >51 μm POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-dominated communities produce large and labile POC aggregates, which generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

Bottom-up versus top-down control in phytoplankton of the Southern Ocean

2004 ◽  
Vol 16 (4) ◽  
pp. 531-539 ◽  
Author(s):  
WALKER O. SMITH ◽  
CHRISTIANE LANCELOT
Keyword(s):  
Southern Ocean ◽  
Functional Groups ◽  
Environmental Control ◽  
Trophic Levels ◽  
Top Down ◽  
Food Web Structure ◽  
Bottom Up ◽  
Physical Forcing ◽  
Phytoplankton Communities ◽  
The Antarctic

Oceanic phytoplankton communities are a mixture of various algal functional groups, all of which are of different sizes, have variable physiologies, and interact differently with disparate herbivores. We suggest that polar plankton communities, and specifically the larger phytoplankton of Southern Ocean HNLC (high nutrient, low chlorophyll) systems, are controlled primarily by bottom-up processes, but that smaller (pico- and nanoplankton) reach an equilibrium that is set simultaneously by light, iron and grazing by microzooplankton. Thus Southern Ocean phytoplankton conforms to the “ecumenical iron hypothesis”, albeit with the further addition of light as an environmental control. Examples of bottom-up controls include iron availability, irradiance regulation (either by the incident surface irradiance as controlled by season and sea ice cover, or by the effects of vertical turbulence and mixed layer depths), and macronutrient availability (silicic acid and nitrate). While the contribution of various phytoplankton taxa varies spatially and temporally within the Antarctic, we suggest that this is largely due to the specific responses of the important functional groups to the patterns of physical forcing and micronutrient inputs, rather than to changes in controls by small and large grazers. Examples of abiotic and biotic controls are examined from representative regions of the Antarctic, including continental shelf regions and open ocean HNLC systems. Results from models further support our contention that bottom-up control of large forms is paramount in the Southern Ocean, but top-down controls play an important part in regulating the equilibrium standing stocks of smaller taxa. If bottom-up control is indeed universal in the Antarctic, then it has profound implications for the understanding of interannual variability, food web structure, and population dynamics of higher trophic levels in both the present and past Southern Ocean.

scholarly journals The Southern Annular Mode (SAM) influences phytoplankton communities in the seasonal ice zone of the Southern Ocean

2020 ◽  
Vol 17 (14) ◽  
pp. 3815-3835
Author(s):  
Bruce L. Greaves ◽  
Andrew T. Davidson ◽  
Alexander D. Fraser ◽  
John P. McKinlay ◽  
Andrew Martin ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Community Composition ◽  
Relative Abundance ◽  
Southern Annular Mode ◽  
Trophic Levels ◽  
Individual Species ◽  
Annular Mode ◽  
Principal Coordinates ◽  
Phytoplankton Communities ◽  
Seasonal Ice Zone

Abstract. Ozone depletion and climate change are causing the Southern Annular Mode (SAM) to become increasingly positive, driving stronger winds southward in the Southern Ocean (SO), with likely effects on phytoplankton habitat due to possible changes in ocean mixing, nutrient upwelling, and sea ice characteristics. This study examined the effect of the SAM and 12 other environmental variables on the abundance of siliceous and calcareous phytoplankton in the seasonal ice zone (SIZ) of the SO. A total of 52 surface-water samples were collected during repeat resupply voyages between Hobart, Australia, and Dumont d'Urville, Antarctica, centred around longitude 142∘ E, over 11 consecutive austral spring–summer seasons (2002–2012), and spanning 131 d in the spring–summer from 20 October to 28 February. A total of 22 taxa groups, comprised of individual species, groups of species, genera, or higher taxonomic groups, were analysed using CAP analysis (constrained analysis of principal coordinates), cluster analysis, and correlation. Overall, satellite-derived estimates of total chlorophyll and measured depletion of macronutrients both indicated a more positive SAM was associated with greater productivity in the SIZ. The greatest effect of the SAM on phytoplankton communities was the average value of the SAM across 57 d in the previous austral autumn centred around 11 March, which explained 13.3 % of the variance in community composition in the following spring–summer. This autumn SAM index was significantly correlated pair-wise (p<0.05) with the relative abundance of 12 of the 22 taxa groups resolved. A more positive SAM favoured increases in the relative abundance of large Chaetoceros spp. that predominated later in the spring–summer and reductions in small diatom taxa and siliceous and calcareous flagellates that predominated earlier in the spring–summer. Individual species belonging to the abundant Fragilariopsis genera responded differently to the SAM, indicating the importance of species-level observation in detecting SAM-induced changes in phytoplankton communities. The day through the spring–summer on which a sample was collected explained a significant and larger proportion (15.4 %) of the variance in the phytoplankton community composition than the SAM, yet this covariate was a proxy for such environmental factors as ice cover and sea surface temperature, factors that are regarded as drivers of the extreme seasonal variability in phytoplankton communities in Antarctic waters. The impacts of SAM on phytoplankton, which are the pasture of the SO and principal energy source for Antarctic life, would have ramifications for both carbon export and food availability for higher trophic levels in the SIZ of the SO.

Extracellular enzymatic activities in the aquatic ecosystems of the Danube Delta. 2. Alkaline phosphatase activity

2021 ◽  
Vol 26 (1) ◽  
pp. 2269-2274
Author(s):  
IOAN PĂCEŞILĂ ◽  
EMILIA RADU
Keyword(s):  
Alkaline Phosphatase ◽  
Water Column ◽  
Aquatic Ecosystems ◽  
Temporal Dynamics ◽  
Extracellular Enzyme ◽  
Danube Delta ◽  
Phytoplankton Communities ◽  
Extracellular Enzymatic Activities ◽  
Adjacent Channels ◽  
Hydrolysis Of

Phosphorus is one of the most important inorganic nutrients in aquatic ecosystems, the development and functioning of the phytoplankton communities being often correlated with the degree of availability in assimilable forms of this element. Alkaline phosphatase (AP) is an extracellular enzyme with nonspecific activity that catalyses the hydrolysis of a large variety of organic phosphate esters and release orthophosphates. During 2011-2013, AP Activity (APA) was assessed in the water column and sediments of several aquatic ecosystems from Danube Delta: Roșu Lake, Mândra Lake and their adjacent channels – Roșu-Împuțita and Roșu-Puiu. The intensity of APA widely fluctuated, ranging between 230-2578 nmol p-nitrophenol L-1h-1 in the water column and 2104-15631 nmol p-nitrophenol g-1h-1 in sediment. Along the entire period of the study, APA was the most intense in Roșu-Împuțita channel, for both water and sediment samples. Temporal dynamics revealed its highest values in summer for the water column and in autumn for sediment. Statistical analysis showed significant seasonal diferences of the APA dynamics in spring vs. summer and autumn for the water column, and any relevant diferences for sediment.

Carbon export associated with free-drifting icebergs in the Southern Ocean

2011 ◽  
Vol 58 (11-12) ◽  
pp. 1485-1496 ◽  
Author(s):  
K.L. Smith ◽  
A.D. Sherman ◽  
T.J. Shaw ◽  
A.E. Murray ◽  
M. Vernet ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Carbon Export

scholarly journals Generalized receptor law governs phototaxis in the phytoplanktonEuglena gracilis

2015 ◽  
Vol 112 (22) ◽  
pp. 7045-7050 ◽  
Author(s):  
Andrea Giometto ◽  
Florian Altermatt ◽  
Amos Maritan ◽  
Roman Stocker ◽  
Andrea Rinaldo
Keyword(s):  
Algal Blooms ◽  
Nonlinear Response ◽  
Temporal Dynamics ◽  
Freshwater Ecosystems ◽  
Trophic Levels ◽  
Light Fields ◽  
Light Sources ◽  
Mathematical Framework ◽  
Heterogeneous Environments ◽  
Light Conditions

Phototaxis, the process through which motile organisms direct their swimming toward or away from light, is implicated in key ecological phenomena (including algal blooms and diel vertical migration) that shape the distribution, diversity, and productivity of phytoplankton and thus energy transfer to higher trophic levels in aquatic ecosystems. Phototaxis also finds important applications in biofuel reactors and microbiopropellers and is argued to serve as a benchmark for the study of biological invasions in heterogeneous environments owing to the ease of generating stochastic light fields. Despite its ecological and technological relevance, an experimentally tested, general theoretical model of phototaxis seems unavailable to date. Here, we present accurate measurements of the behavior of the algaEuglena graciliswhen exposed to controlled light fields. Analysis ofE. gracilis’ phototactic accumulation dynamics over a broad range of light intensities proves that the classic Keller–Segel mathematical framework for taxis provides an accurate description of both positive and negative phototaxis only when phototactic sensitivity is modeled by a generalized “receptor law,” a specific nonlinear response function to light intensity that drives algae toward beneficial light conditions and away from harmful ones. The proposed phototactic model captures the temporal dynamics of both cells’ accumulation toward light sources and their dispersion upon light cessation. The model could thus be of use in integrating models of vertical phytoplankton migrations in marine and freshwater ecosystems, and in the design of bioreactors.

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