scholarly journals Ocean acidification reduces growth and grazing impact of Antarctic heterotrophic nanoflagellates

2020 ◽  
Vol 17 (16) ◽  
pp. 4153-4171
Author(s):  
Stacy Deppeler ◽  
Kai G. Schulz ◽  
Alyce Hancock ◽  
Penelope Pascoe ◽  
John McKinlay ◽  
...  
Keyword(s):  
Ocean Acidification ◽  
Food Web ◽  
Microbial Communities ◽  
Heterotrophic Bacteria ◽  
Trophic Levels ◽  
Heterotrophic Nanoflagellates ◽  
Grazing Impact ◽  
Antarctic Marine ◽  
Morphological Differences ◽  
Organic Matter Recycling

Abstract. High-latitude oceans have been identified as particularly vulnerable to ocean acidification if anthropogenic CO2 emissions continue. Marine microbes are an essential part of the marine food web and are a critical link in biogeochemical processes in the ocean, such as the cycling of nutrients and carbon. Despite this, the response of Antarctic marine microbial communities to ocean acidification is poorly understood. We investigated the effect of increasing fCO2 on the growth of heterotrophic nanoflagellates (HNFs), nano- and picophytoplankton, and prokaryotes (heterotrophic Bacteria and Archaea) in a natural coastal Antarctic marine microbial community from Prydz Bay, East Antarctica. At CO2 levels ≥634 µatm, HNF abundance was reduced, coinciding with increased abundance of picophytoplankton and prokaryotes. This increase in picophytoplankton and prokaryote abundance was likely due to a reduction in top-down control of grazing HNFs. Nanophytoplankton abundance was elevated in the 634 µatm treatment, suggesting that moderate increases in CO2 may stimulate growth. The taxonomic and morphological differences in CO2 tolerance we observed are likely to favour dominance of microbial communities by prokaryotes, nanophytoplankton, and picophytoplankton. Such changes in predator–prey interactions with ocean acidification could have a significant effect on the food web and biogeochemistry in the Southern Ocean, intensifying organic-matter recycling in surface waters; reducing vertical carbon flux; and reducing the quality, quantity, and availability of food for higher trophic levels.

scholarly journals Ocean acidification reduces growth and grazing of Antarctic heterotrophic nanoflagellates

2019 ◽  
Author(s):  
Stacy Deppeler ◽  
Kai G. Schulz ◽  
Alyce Hancock ◽  
Penelope Pascoe ◽  
John McKinlay ◽  
...  
Keyword(s):  
Ocean Acidification ◽  
Food Web ◽  
Heterotrophic Nanoflagellates ◽  
Marine Microbes ◽  
Predator Prey ◽  
Marine Food Web ◽  
Antarctic Marine ◽  
Growth Changes ◽  
Organic Matter Recycling ◽  
Marine Microbial Communities

Abstract. High-latitude oceans have been identified as particularly vulnerable to ocean acidification if anthropogenic CO2 emissions continue. Marine microbes are an essential part of the marine food web and are a critical link in biogeochemical processes in the ocean, such as the cycling of nutrients and carbon. Despite this, the response of Antarctic marine microbial communities to ocean acidification is poorly understood. We investigated the effect of increasing fCO2 on the growth of heterotrophic nanoflagellates (HNF), nano- and picophytoplankton, and prokaryotes in a natural coastal Antarctic marine microbial community from Prydz Bay, East Antarctica. At CO2 levels ≥ 634 μatm, HNF abundance was reduced, coinciding with significantly increased abundance of picophytoplankton and prokaryotes. This increase in picophytoplankton and prokaryote abundance was likely due to a reduction in top-down control of grazing HNF. Nanophytoplankton abundance was significantly elevated in the 634 and 953 μatm treatments, suggesting that moderate increases in CO2 may stimulate growth. Changes in predator-prey interactions with ocean acidification could have a significant effect on the food web and biogeochemistry in the Southern Ocean. Based on these results, it is likely that the phytoplankton community composition in these waters will shift to communities dominated by prokaryotes, nano- and picophytoplankton. This may intensify organic matter recycling in surface waters, leading to a decline in carbon flux, as well as a reducing the quality and quantity of food available to higher trophic organisms.

An Inverse Model Analysis of Planktonic Food Webs in Experimental Lakes

1994 ◽  
Vol 51 (9) ◽  
pp. 2034-2044 ◽  
Author(s):  
Alain F. Vézina ◽  
Michael L. Pace
Keyword(s):  
Food Web ◽  
Heterotrophic Bacteria ◽  
Grazing Pressure ◽  
Inverse Methods ◽  
Trophic Levels ◽  
Microbial Food Web ◽  
Food Web Structure ◽  
Planktonic Food ◽  
Size Groups ◽  
The Impact

We used inverse methods to reconstruct carbon flows in experimental lakes where the fish community had been purposely altered. These analyses were applied to three years of data from a reference lake and two experimental lakes located in Gogebic County, Michigan. We reconstructed seasonally averaged flows among two size groups of phytoplankton, heterotrophic bacteria, microzooplankton, cladocerans, and copepods. The inverse analysis produced significantly different flow networks for the different lakes that agreed qualitatively with known chemical and biological differences between lakes and with other analyses of the impact of fish manipulations on food web structure and dynamics. The results pointed to alterations in grazing pressure on the phytoplankton that parallel changes in the size and abundance of cladocerans and copepods among lakes. Estimated flows through the microbial food web indicated low bacterial production efficiencies and small carbon transfers from the microbial food web to the larger zooplankton. This study demonstrates the use of inverse methods to identify and compare flow patterns across ecosystems and suggests that microbial flows are relatively insensitive to changes at the upper trophic levels.

scholarly journals Transfer of diazotroph-derived nitrogen to the planktonic food web across gradients of N<sub>2</sub> fixation activity and diversity in the western tropical South Pacific Ocean

2018 ◽  
Vol 15 (12) ◽  
pp. 3795-3810 ◽  
Author(s):  
Mathieu Caffin ◽  
Hugo Berthelot ◽  
Véronique Cornet-Barthaux ◽  
Aude Barani ◽  
Sophie Bonnet
Keyword(s):  
Food Web ◽  
N2 Fixation ◽  
Secondary Ion Mass Spectrometry ◽  
Heterotrophic Bacteria ◽  
South Pacific ◽  
Open Ocean ◽  
Trophic Levels ◽  
Planktonic Food ◽  
South Pacific Ocean ◽  
Fixation Activity

Abstract. Biological dinitrogen (N2) fixation provides the major source of new nitrogen (N) to the open ocean, contributing more than atmospheric deposition and riverine inputs to the N supply. Yet the fate of the diazotroph-derived N (DDN) in the planktonic food web is poorly understood. The main goals of this study were (i) to quantify how much of DDN is released to the dissolved pool during N2 fixation and how much is transferred to bacteria, phytoplankton and zooplankton, and (ii) to compare the DDN release and transfer efficiencies under contrasting N2 fixation activity and diversity in the oligotrophic waters of the western tropical South Pacific (WTSP) Ocean. We used nanometre-scale secondary ion mass spectrometry (nanoSIMS) coupled with 15N2 isotopic labelling and flow cytometry cell sorting to track the DDN transfer to plankton, in regions where the diazotroph community was dominated by either Trichodesmium or by UCYN-B. After 48 h, ∼ 20–40 % of the N2 fixed during the experiment was released to the dissolved pool when Trichodesmium dominated, while the DDN release was not quantifiable when UCYN-B dominated; ∼ 7–15 % of the total fixed N (net N2 fixation + release) was transferred to non-diazotrophic plankton within 48 h, with higher transfer efficiencies (15 ± 3 %) when UCYN-B dominated as compared to when Trichodesmium dominated (9 ± 3 %). The pico-cyanobacteria Synechococcus and Prochlorococcus were the primary beneficiaries of the DDN transferred (∼ 65–70 %), followed by heterotrophic bacteria (∼ 23–34 %). The DDN transfer in bacteria was higher (34 ± 7 %) in the UCYN-B-dominating experiment compared to the Trichodesmium-dominating experiments (24 ± 5 %). Regarding higher trophic levels, the DDN transfer to the dominant zooplankton species was less efficient when the diazotroph community was dominated by Trichodesmium (∼ 5–9 % of the DDN transfer) than when it was dominated by UCYN-B (∼ 28 ± 13 % of the DDN transfer). To our knowledge, this study provides the first quantification of DDN release and transfer to phytoplankton, bacteria and zooplankton communities in open ocean waters. It reveals that despite UCYN-B fix N2 at lower rates compared to Trichodesmium in the WTSP, the DDN from UCYN-B is much more available and efficiently transferred to the planktonic food web than the DDN originating from Trichodesmium.

scholarly journals Plankton in the open Mediterranean Sea: a review

2009 ◽  
Vol 6 (6) ◽  
pp. 11187-11292 ◽  
Author(s):  
I. Siokou-Frangou ◽  
U. Christaki ◽  
M. G. Mazzocchi ◽  
M. Montresor ◽  
M. Ribera d'Alcalá ◽  
...  
Keyword(s):  
Food Web ◽  
Mediterranean Sea ◽  
Deep Convection ◽  
Trophic Levels ◽  
Grazing Impact ◽  
Late Winter ◽  
Amazon Forest ◽  
Chl A ◽  
Spatial And Temporal Scales ◽  
The Mediterranean

Abstract. We present an overview of the plankton studies conducted during the last 25 years in the epipelagic offshore waters of the Mediterranean Sea. This quasi-enclosed sea is characterized by a rich and complex physical dynamics that includes unique thermohaline features, particular multilayer circulation, topographic gyres, and meso- and sub-mesoscale activity. Recent investigations have basically confirmed the long-recognised oligotrophic character of this sea, which enhances along both the west-east, and the north-south directions. Nutrient availability is low, especially for phosphorous (N:P up to 60), although limitation may be relaxed by inputs from highly populated coasts and from the atmosphere. Phytoplankton biomass as chl-a, generally displays low values (less than 0.2 μg chl-a l-1) over large areas, with a modest late winter increase. A large bloom (up to 3 μg l-1) throughout the late winter and early spring is only observed in the NW area. Relatively high biomass peaks are also recorded in fronts and cyclonic gyres. A deep chlorophyll maximum is a~permanent feature for the whole basin (except during the late winter mixing). It progressively deepens from the Alboran Sea (30 m) to the easternmost Levantine basin (120 m). Primary production reveals a similar west-east decreasing trend and ranges from 59 to 150 g C m-2 y-1 (in situ measurements). Overall the basin is largely dominated by small-sized autotrophs, microheterotrophs and egg-carrying copepod species. The phytoplankton, the microbial (both autotrophic and heterotrophic) and the zooplankton components reveal a considerable diversity and variability over spatial and temporal scales, the latter less explored though. Examples are the wide diversity of dinoflagellates and coccolithophores, the multifarious role of diatoms or picoeukaryotes, and the distinct seasonal or spatial patterns of the species-reach copepod genera or families which dominate in the basin. Major dissimilarities between western and eastern basins have been highlighted in species composition of phytoplankton and mesozooplankton, but also in the microbial components and in their relationships. Superimposed to these longitudinal differences, a pronounced biological heterogeneity is also observed in areas hosting deep convection, fronts, cyclonic and anti-cyclonic gyres or eddies. There, the intermittent nutrient enrichment promotes switches from a small-sized microbial community to diatom-dominated populations. A classical food web is ready to substitute the microbial food web in these cases. These switches, likely occurring within a continuum of trophic pathways, may greatly enhance the flux towards high trophic levels, in spite of an apparent heterotrophy. Basically, the system seems to be top-down controlled and characterised by a ‘multivorous web’, as shown by the great variety of feeding modes and preferences and by the significant and simultaneous grazing impact on phytoplankton and ciliates by mesozooplankton. ‘La Mediterrània, o almenys la seva zona pelàgica, seria comparable a una Amazònia marina.’ (Margalef, 1995) (The Mediterranean, or at least its pelagic zone, would be like a marine version of the Amazon forest.)

scholarly journals Temporal variability of the microbial food web (viruses to ciliates) under the influence of the Black Sea Water inflow (N. Aegean, E. Mediterranean)

2014 ◽  
Vol 15 (4) ◽  
pp. 769 ◽  
Author(s):  
A. GIANNAKOUROU ◽  
A. TSIOLA ◽  
M. KANELLOPOULOU ◽  
I. MAGIOPOULOS ◽  
I. SIOKOU ◽  
...  
Keyword(s):  
Food Web ◽  
Black Sea ◽  
Bacterial Production ◽  
Heterotrophic Bacteria ◽  
Sea Water ◽  
Phytoplankton Bloom ◽  
Aegean Sea ◽  
Trophic Levels ◽  
Microbial Food Web ◽  
The Black Sea

Τhe entire pelagic microbial food web was studied during the winter-spring period in the frontal area of the North Aegean Sea. Abundance of viruses, heterotrophic bacteria, cyanobacteria, auto- and hetero-trophic flagellates, and ciliates, as well as bacterial production, were measured at three stations (MD1, MD2, MD3) situated along a N-S transect between the area directly influenced by the inflowing Black Sea water and the area covered by the Levantine water. Samples were collected in December 2009, and January, March, April, and May 2011. Station MD1 exhibited the highest values of abundance and integrated biomass of all microbial groups and bacterial production during all months, and MD3 the lowest. Bacteria dominated the total integrated biomass at all stations and months, followed by cyanobacteria, auto-, hetero-trophic flagellates and ciliates. On a temporal scale, the microbial food web was less important in March as all microbial parameters at all stations showed the lowest values. After the phytoplankton bloom in March, the heterotrophic part of the microbial food web (mainly) strongly increased, though the intensity of the phenomenon was diminished from North to South. Pico-sized plankton was found to be heterotrophic whereas nanoplankton was autotrophic. It seems that the influence of the Black Sea water on station MD1, permanent throughout the study period of early winter to late spring, was reflected in all microbial populations studied, and produced a more productive pelagic food web system, with potential consequences for the upper trophic levels.

scholarly journals Plankton in the open Mediterranean Sea: a review

2010 ◽  
Vol 7 (5) ◽  
pp. 1543-1586 ◽  
Author(s):  
I. Siokou-Frangou ◽  
U. Christaki ◽  
M. G. Mazzocchi ◽  
M. Montresor ◽  
M. Ribera d'Alcalá ◽  
...  
Keyword(s):  
Food Web ◽  
Mediterranean Sea ◽  
Thermohaline Circulation ◽  
Deep Convection ◽  
Trophic Levels ◽  
Grazing Impact ◽  
Late Winter ◽  
Chl A ◽  
Spatial And Temporal Scales ◽  
The North

Abstract. We present an overview of the plankton studies conducted during the last 25 years in the epipelagic offshore waters of the Mediterranean Sea. This quasi-enclosed sea is characterized by a rich and complex physical dynamics with distinctive traits, especially in regard to the thermohaline circulation. Recent investigations have basically confirmed the long-recognised oligotrophic nature of this sea, which increases along both the west-east and the north-south directions. Nutrient availability is low, especially for phosphorous (N:P up to 60), though this limitation may be buffered by inputs from highly populated coasts and from the atmosphere. Phytoplankton biomass, as chl a, generally displays low values (less than 0.2 μg chl a l−1) over large areas, with a modest late winter increase. A large bloom (up to 3 μg l−1) is observed throughout the late winter and spring exclusively in the NW area. Relatively high biomass values are recorded in fronts and cyclonic gyres. A deep chlorophyll maximum is a permanent feature for the whole basin, except during the late winter mixing. It is found at increasingly greater depths ranging from 30 m in the Alboran Sea to 120 m in the easternmost Levantine basin. Primary production reveals a west-east decreasing trend and ranges between 59 and 150 g C m−2 y−1 (in situ measurements). Overall, the basin is largely dominated by small autotrophs, microheterotrophs and egg-carrying copepod species. The microorganisms (phytoplankton, viruses, bacteria, flagellates and ciliates) and zooplankton components reveal a considerable diversity and variability over spatial and temporal scales, although the latter is poorly studied. Examples are the wide diversity of dinoflagellates and coccolithophores, the multifarious role of diatoms or picoeukaryotes, and the distinct seasonal or spatial patterns of the species-rich copepod genera or families which dominate the basin. Major dissimilarities between western and eastern basins have been highlighted in species composition of phytoplankton and mesozooplankton, but also in the heterotrophic microbial components and in their relationships. Superimposed to these longitudinal differences, a pronounced biological heterogeneity is also observed in areas hosting deep convection, fronts, cyclonic and anti-cyclonic gyres or eddies. In such areas, the intermittent nutrient enrichment promotes a switching between a small-sized microbial community and diatom-dominated populations. A classical food web readily substitutes the microbial food web in these cases. These switches, likely occurring within a continuum of trophic pathways, may greatly increase the flux towards higher trophic levels, in spite of the apparent heterotrophy. Basically, the microbial system seems to be both bottom-up and top-down controlled. A "multivorous web" is shown by the great variety of feeding modes and preferences and by the significant and simultaneous grazing impact on phytoplankton and ciliates by mesozooplankton.

scholarly journals Microbial food web dynamics during spring phytoplankton blooms in the naturally iron-fertilized Kerguelen area (Southern Ocean)

2014 ◽  
Vol 11 (23) ◽  
pp. 6739-6753 ◽  
Author(s):  
U. Christaki ◽  
D. Lefèvre ◽  
C. Georges ◽  
J. Colombet ◽  
P. Catala ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Food Web ◽  
Bacterial Production ◽  
Trophic Levels ◽  
Microbial Food Web ◽  
Heterotrophic Nanoflagellates ◽  
Viral Production ◽  
Phytoplankton Blooms ◽  
Food Web Dynamics ◽  
Heterotrophic Production

Abstract. Microbial food web dynamics were determined during the onset of several spring phytoplankton blooms induced by natural iron fertilization off Kerguelen Island in the Southern Ocean (KEOPS2). The abundances of heterotrophic bacteria and heterotrophic nanoflagellates, bacterial heterotrophic production, bacterial respiration, and bacterial growth efficiency, were consistently higher in surface waters of the iron-fertilized sites than at the reference site in HNLC (high nutrient low chlorophyll) waters. The abundance of virus-like particles remained unchanged, but viral production increased by a factor of 6 in iron-fertilized waters. Bacterial heterotrophic production was significantly related to heterotrophic nanoflagellate abundance and viral production across all sites, with bacterial production explaining about 70 and 85%, respectively, of the variance of each in the mixed layer (ML). Estimated rates of grazing and viral lysis, however, indicated that heterotrophic nanoflagellates accounted for a substantially higher loss of bacterial production (50%) than viruses (11%). Combining these results with rates of primary production and export determined for the study area, a budget for the flow of carbon through the microbial food web and higher trophic levels during the early (KEOPS2) and the late phase (KEOPS1) of the Kerguelen bloom is provided.

scholarly journals Macromolecular composition, productivity and dimethylsulfoniopropionate in Antarctic pelagic and sympagic microalgal communities

2020 ◽  
Vol 640 ◽  
pp. 45-61 ◽  
Author(s):  
CE Sheehan ◽  
DA Nielsen ◽  
K Petrou
Keyword(s):  
Food Web ◽  
Unsaturated Fatty Acids ◽  
High Energy ◽  
Photosynthetic Performance ◽  
Trophic Levels ◽  
Marine Food Web ◽  
Antarctic Marine ◽  
Lyase Activity ◽  
Near Shore ◽  
Macromolecular Composition

Microalgae form the base of the Antarctic marine food web and through their conversion of nutrients into biomass, are the principal source of energy for higher trophic levels. Environmental conditions strongly influence microalgal photophysiology, biochemistry and macromolecular composition, which has implications for the quality and quantity of energy available for transfer through the food web. Here we assessed the photosynthetic performance, biochemical (dimethylsulfoniopropionate; DMSP) and macromolecular composition (lipids, carbohydrates and proteins) of selected diatoms sampled from 2 distinct Antarctic marine environments, namely the late spring bottom sea ice (sympagic) and near-shore ice-free coastal waters (pelagic). The photosynthetic efficiency and photoprotective capacity of the communities differed significantly, and chlorophyll a-specific gross primary productivity was 4-fold greater in the pelagic community. At the community level, pelagic microalgae had the highest DMSP content (1.4 nmol [µg chl a]-1) and the highest potential rates of DMSP lyase activity (0.87 nmol [µg chl a]-1 h-1). Comparisons within each community showed taxon-specific differences in macromolecular composition, which were strongest amongst the sympagic diatoms. Comparing across communities, pelagic diatoms had lower lipid to protein ratios, whereas sympagic diatoms were lipid rich and had significantly higher content of unsaturated fatty acids. These findings show variability in the physiology and nutritional quality of the base of the food web depending on habitat and taxonomic group and emphasise the importance of the sympagic community for providing a concentrated source of high-energy compounds during the pulsed productivity events for key grazers such as krill to survive through long dark winters.

scholarly journals Contrasting effects of ocean acidification on the microbial food web under different trophic conditions

2015 ◽  
Vol 73 (3) ◽  
pp. 670-679 ◽  
Author(s):  
M. M. Sala ◽  
F. L. Aparicio ◽  
V. Balagué ◽  
J. A. Boras ◽  
E. Borrull ◽  
...  
Keyword(s):  
Ocean Acidification ◽  
Microbial Communities ◽  
Heterotrophic Bacteria ◽  
Phytoplankton Bloom ◽  
Extracellular Enzyme ◽  
Nutrient Concentrations ◽  
Leucine Incorporation ◽  
Negative Effects ◽  
Trophic Conditions ◽  
Positive Effects

AbstractWe investigated the effects of an increase in dissolved CO2 on the microbial communities of the Mediterranean Sea during two mesocosm experiments in two contrasting seasons: winter, at the peak of the annual phytoplankton bloom, and summer, under low nutrient conditions. The experiments included treatments with acidification and nutrient addition, and combinations of the two. We followed the effects of ocean acidification (OA) on the abundance of the main groups of microorganisms (diatoms, dinoflagellates, nanoeukaryotes, picoeukaryotes, cyanobacteria, and heterotrophic bacteria) and on bacterial activity, leucine incorporation, and extracellular enzyme activity. Our results showed a clear stimulation effect of OA on the abundance of small phytoplankton (pico- and nanoeukaryotes), independently of the season and nutrient availability. A large number of the measured variables showed significant positive effects of acidification in summer compared with winter, when the effects were sometimes negative. Effects of OA were more conspicuous when nutrient concentrations were low. Our results therefore suggest that microbial communities in oligotrophic waters are considerably affected by OA, whereas microbes in more productive waters are less affected. The overall enhancing effect of acidification on eukaryotic pico- and nanophytoplankton, in comparison with the non-significant or even negative response to nutrient-rich conditions of larger groups and autotrophic prokaryotes, suggests a shift towards medium-sized producers in a future acidified ocean.

scholarly journals Combining mesocosms with models to unravel the effects of global warming and ocean acidification on temperate marine ecosystems

2020 ◽  
Author(s):  
Hadayet Ullah ◽  
Ivan Nagelkerken ◽  
Silvan U. Goldenberg ◽  
Damien Fordham
Keyword(s):  
Climate Change ◽  
Global Change ◽  
Ocean Acidification ◽  
Food Web ◽  
Marine Ecosystems ◽  
Ocean Warming ◽  
Trophic Levels ◽  
Individual Species ◽  
Combined Effects ◽  
Biodiversity Change

Ocean warming and species exploitation have already caused large-scale reorganization of biological communities across the world. Accurate projections of future biodiversity change require a comprehensive understanding of how entire communities respond to global change. We combined a time-dynamic integrated food web modelling approach (Ecosim) with a community-level mesocosm experiment to determine the independent and combined effects of ocean warming and acidification, and fisheries exploitation, on a temperate coastal ecosystem. The mesocosm enabled important physiological and behavioural responses to climate stressors to be projected for trophic levels ranging from primary producers to top predators, including sharks. We show that under current-day rates of exploitation, warming and ocean acidification will benefit most species in higher trophic levels (e.g. mammals, birds, demersal finfish) in their current climate ranges, with the exception of small pelagic fish, but these benefits will be reduced or lost when these physical stressors co-occur. We show that increases in exploitation will, in most instances, suppress any positive effects of human-driven climate change, causing individual species biomass to decrease at high-trophic levels. Species diversity at the trailing edges of species distributions is likely to decline in the face of ocean warming, acidification and exploitation.We showcase how multi-level mesocosm food web experiments can be used to directly inform dynamic food web models, enabling the ecological processes that drive the responses of marine ecosystems to scenarios of global change to be captured in model projections and their individual and combined effects to be teased apart. Our approach for blending theoretical and empirical results from mesocosm experiments with computational models will provide resource managers and conservation biologists with improved tools for forecasting biodiversity change and altered ecosystem processes due to climate change.

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