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Variability and interactions of phytoplankton and bacterioplankton in the Antarctic neritic area
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The distributions of phytoplankton biomass and bacterial populations were investigated at 37 stations on the continental shelf of Terre Adelie (Antarctica) during Austral summer 1989. Despite a potentially favourable environment, phytoplankton biomass was relatively low. Surface chlorophyll a values ranged from 1.2 mg m-3 in the coastal area, with a maximum of 2.5 mg m-3 in the vicinity of the penguin rookeries, to only 0.2 mg m-3 70 km offshore. In the Pointe Geologie Archipelago, diatoms larger than 10 mum were predominant and represented more than 80 % of the total biomass. In off shore waters, these large cells represented only 38 % of the total biomass with 59 % of the biomass in the 1 to 10 mum fraction. Total bacterial abundance ranged from 9.4 x 10(9) to 1.0 x 10(11) cells m-3 and heterotrophic bacteria ranged from 1.4 x 10(6) to 7.7 x 10(8) colony forming units m-3. Frequency of dividing cells ranged from 0.8 to 6.6 %. The highest numbers of heterotrophic bacteria were recorded in the immediate vicinity of penguin rookeries and the lowest in offshore waters. Bacterial biomass represents between 2 to 15 % of total microbial biomass in offshore waters and up to 30 % in the coastal area. There was no direct correlation between bacterial and phytoplanktonic standing stocks. This lack of relationship can be explained by considering the differences in scale. It is suggested that in the coastal area where large diatoms are dominant, the bacteria are mainly dependant on organic matter introduced by bird manuring. On the other hand, in offshore waters where the dominant phytoplankton fraction under 10 mum represents a large part of the microbial loop, an indirect relationship between algae and bacteria may be expected.
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... In Antarctic coastal environments, most phytoplankton studies have been undertaken during summer (December-February) for logistical reasons because this is a period of maximum change in planktonic algal assemblages (Dayton et al. 1986;Fiala and Delille 1992;Brandini and Rebello 1994;Kang et al. 1997Kang et al. , 2002. These previous studies have generally been based on short-term observations of only several years, and continuous year-round monitoring studies have rarely been conducted in Antarctic coastal stations (Clarke et al. 1988;Kopczyńska 2008;Montes-Hugo et al. 2009). ...
... Macro-nutrients were generally abundant throughout the season and were relatively higher than those reported previously in other Antarctic coastal regions (Nelson et al. 8 lM), and silicic acid (63.0 lM) normally occurred during the phytoplankton growth season from December to January (Fig. 3). Fiala and Delille (1992) reported that the concentration ranges in the vicinity of the coast of Terre Adélie were 20 to 25 lM, 2 to 2.5 lM, and 45 to 60 lM for nitrate, phosphate, and silicate, respectively. However, the range of the nutrient concentrations reported in this study (with the exception of particularly low nitrate concentrations; 12.1 lM in December 2003; data not shown) was more similar to those from two sampling sites in Borge Bay, Signy Island, from 1969 to 1982 (Clarke et al. 1988). ...
... The overall annual mean of the surface total chl-a concentration was 0.57 mg chl-a m -3 (SD = ±0.59 mg chl-a m -3 ) in this study, which coincides with the lower range of chl-a concentration reported in the vicinity of the coast of Terre Adélie by Fiala and Delille (1992). The annual mean of the total surface chl-a concentration in this study was lower than that of Kang et al. (2002) (1.38 mg chl-a m -3 ) from the same site based on data from 1996. ...
To detect and monitor coastal marine ecosystem responses to current environmental changes, the phytoplankton assemblage, salinity, and macro-nutrients were monitored daily at a fixed coastal site in Marian Cove, Antarctica, from 1996 to 2008. The monthly average water temperature at the site was highest (2.14 ± 0.36 °C) during the summer period (December–February) and lowest (−1.80 ± 0.22 °C) during the winter period (July–September). The salinity levels exhibited the opposite trend with the lowest values (30.9 ± 0.68 psu) during summer and the highest values (35.2 ± 1.15 psu) during winter. The concentrations of major nutrients were always high enough for phytoplankton growth, indicating the nutrients are not a main controlling factor for phytoplankton growth. Total chlorophyll-a generally started to increase from late November with a peak (1.14 ± 1.41 mg chl-a m−3) around January when the water temperature was the warmest during the year. Within the phytoplankton communities, the average contribution of small (nano- plus pico-) phytoplankton (<20 μm) to the total chl-a concentration was high (62.9 %) throughout the study period, which supports the observation that small phytoplankton contributed 85.7 % to the cell numbers and 56.4 % to the biovolume of the total phytoplankton. The high contribution of small phytoplankton is a general characteristic at Marian Cove and may be expected to increase under future warming conditions.
... Early work in Antarctic waters revealed that bacterial biomass might represent up to 30% of total microbial biomass in coastal areas (Fiala and Delille, 1992). In Antarctica, free-living marine microbial community composition can differ significantly between locations at relatively small spatial and temporal scales, responding to environmental variations of temperature, salinity, nutrients, or the presence of oceanic fronts (see for example, the Supplementary Material of Lozupone and Knight, 2007;Raes et al., 2018). ...
Primary productivity in the Ross Sea region is characterized by intense phytoplankton blooms whose temporal and spatial distribution are driven by changes in environmental conditions as well as interactions with the bacterioplankton community. However, the number of studies reporting the simultaneous diversity of the phytoplankton and bacterioplankton in Antarctic waters are limited. Here, we report data on the bacterial diversity in relation to phytoplankton community structure in the surface waters of the Ross Sea during the Austral summer 2017. Our results show partially overlapping bacterioplankton communities between the stations located in the Terra Nova Bay (TNB) coastal waters and the Ross Sea Open Waters (RSOWs), with a dominance of members belonging to the bacterial phyla Bacteroidetes and Proteobacteria. In the TNB coastal area, microbial communities were characterized by a higher abundance of sequences related to heterotrophic bacterial genera such as Polaribacter spp., together with higher phytoplankton biomass and higher relative abundance of diatoms. On the contrary, the phytoplankton biomass in the RSOW were lower, with relatively higher contribution of haptophytes and a higher abundance of sequences related to oligotrophic and mixothrophic bacterial groups like the Oligotrophic Marine Gammaproteobacteria (OMG) group and SAR11. We show that the rate of diversity change between the two locations is influenced by both abiotic (salinity and the nitrogen to phosphorus ratio) and biotic (phytoplankton community structure) factors. Our data provide new insight into the coexistence of the bacterioplankton and phytoplankton in Antarctic waters, suggesting that specific rather than random interaction contribute to the organic matter cycling in the Southern Ocean.
... Early work in Antarctic waters revealed that bacterial biomass might represent up to 30 % of total microbial biomass in coastal areas (Fiala and Delille, 1992). In Antarctica, free-living marine microbial community composition can differ significantly between locations at relatively small spatial and temporal scales, responding to environmental variations of temperature, salinity, nutrients, or the presence of oceanic fronts (Lozupone and Knight, 2007;Nemergut et al., 2011;Raes et al., 2018). ...
Primary productivity in the Ross Sea region is characterized by intense phytoplankton blooms whose temporal and spatial distribution are driven by changes in environmental conditions as well as interactions with the bacterioplankton community. Exchange of exudates, metabolism by-products and cofactors between the phytoplankton and the bacterioplankton communities drive a series of complex interactions affecting the micronutrient availability and co-limitation, as well as nutrient uptakes in Antarctic waters. Yet, the number of studies reporting the simultaneous diversity of the phytoplankton and bacterioplankton in Antarctic waters are limited. Here we report data on the bacterial diversity in relation to phytoplankton community in the surface waters of the Ross Sea during the austral summer 2017. Our results show partially overlapping bacterioplankton communities between the stations located in the Terra Nova Bay coastal waters and the Ross Sea open waters, suggesting that the two communities are subjected to different drivers. We show that the rate of diversity change between the two locations is influenced by both abiotic (salinity and the nitrogen to phosphorus ratio) and biotic (phytoplankton community structure) factors. Our data provides new insight into the coexistence of the bacterioplankton and phytoplankton in Antarctic waters.
... This influence is most likely mediated by variations in the quantity and/or bioavailability of organic matter generated by the primary producers, which is proposed to vary according to phytoplankton taxa (Moline and Prezelin, 1996), and may affect bacterioplankton biomass and composition (Tada et al., 2013). Indeed, the bioavailability of photosynthate to secondary producers has been proposed as an alternative explanation for the decoupling of primary and secondary producers in Antarctic waters (Fiala and Delille, 1992). Drawdown of macronutrients by phytoplankton requires iron to be available, and interannual variation in summer macronutrient minima could be indicative of variable iron supply from melting glaciers . ...
An eight year time-series in the Western Antarctic Peninsula (WAP) with an approximately weekly sampling frequency was used to elucidate changes in virioplankton abundance and their drivers in this climatically-sensitive region. Virioplankton abundances at the coastal WAP show a pronounced seasonal cycle with interannual variability in the timing and magnitude of the summer maxima. Bacterioplankton abundance is the most influential driving factor of the virioplankton, and exhibit closely coupled dynamics. Sea ice cover and duration predetermine levels of phytoplankton stock and thus, influence virioplankton by dictating the substrates available to the bacterioplankton. However, variations in the composition of the phytoplankton community and particularly the prominence of Diatoms inferred from silicate drawdown, drive inter-annual differences in the magnitude of the virioplankton bloom; likely again mediated through changes in the bacterioplankton. Our findings suggest that future warming within the WAP will cause changes in sea ice that will influence viruses and their microbial hosts through changes in the timing, magnitude and composition of the phytoplankton bloom. Thus the flow of matter and energy through the viral shunt may be decreased with consequences for the Antarctic food web and element cycling. This article is protected by copyright. All rights reserved.
... Oceanographic data for the coastal shelf of Adelie Land are scarce: some hydrological data are available from a summer cruise (Tchernia 195 1) and taxonomic investigations, mostly for pelagic diatoms, were conducted during the same cruise by Manguin (1960). The phytoplankton is characterized by low biomass (on an average 1.23 pg chl a 1.' in summer; Fiala & Delille 1992), and the ice pigment biomass, studied over one year at a neritic site sheltered between islands, is also low (maximum 40 kg chl a 1.' at spring; Delille eta/. 1995). ...
Land-fast ice in the vicinity of Adélie Land was sampled during spring 1995. The ice was annual, thin, with no consistent snow cover, and exposed to oceanic conditions. Temporal and spatial variations of the vertical pigment distribution were studied in relation to environmental factors, during the break up of the ice. Different levels were sampled in the congelation ice and the platelet ice-like layer (PLI). Under-ice water and open water masses were also sampled. The algal biomass was greater in the PLI (24 ±14 1 offshore and up to 9 mg chl a lg chl al2 near the coast and 0.8 mg m300 100 1. At very low biomass and cell densities 2 104 cells l2 near-shore) was transferred to the underlying water masses (on an average 15 t POC km−1 shoreline).
... Heterotrophic bacteria are the major consumers of oceanic dissolved organic matter; therefore, they are potential users of the mostly labile DPP (Amon et al. 2001). Several studies have documented this trophic link in Antarctic waters with divergent conclusions about the time scale and degree of bacterial dependence on DPP (Fiala and Delille 1992;Bird and Karl 1999;Morá n et al. 2002). Such differences are partly because of seasonal changes (Stewart and Fritsen 2004). ...
We examined the potential response of Southern Ocean pelagic ecosystems to warming through changes in total primary production (particulate plus dissolved = PPP + DPP) and bacterial production (BP), determined simultaneously at ambient temperature ( $-1.4 to 0.4\textdegree C$ ) and at $2\textdegree C$ in eight experiments performed near the Antarctic Peninsula in late spring 2002. Short (<6 h) time course experiments of radiocarbon uptake and photosynthesis-irradiance relationships consistently showed that a significant amount of photosynthate appeared as dissolved substances, with a mean 35% extracellular release (PER). Whereas PPP remained virtually unchanged ( $0.7 mg C m^{-3} h^{-1}$ ), DPP increased significantly at $2\textdegree C$ from $0.5 to 0.9 mg C m^{-3} h^{-1}$ . The corresponding increase in PER (54% on average) was significantly and positively correlated with the temperature difference among treatments, suggesting that an increase in DPP could be expected with a temperature rise in the Southern Ocean. BP, estimated via $[^3H] leucine$ incorporation, tended to increase at $2\textdegree C$ only at low absolute values, and this increment was inversely related to PPP. However, our results show that the estimated bacterial carbon demand (BCD) was generally well below concurrent DPP at both treatments (mean BCD:DPP ratios of 0.60 and 0.27 at ambient temperature and $2\textdegree C$ , respectively), indicating that temperature-related extra inputs of organic substrates were not fully and immediately processed by bacteria. To the extent that these results reflect general ecophysiological trends, warming of Southern Ocean surface waters could produce changes in plankton-mediated biogeochemical processes leading to a greater importance of dissolved organic matter fluxes.
... However, rich microalgal assemblages can develop at the surface of sea ice within areas of submerged ice that are infiltrated with seawater (Ackley et al. 1979). Indeed, microalgal biomass can reach levels considerably greater than those found in the underlying seawater (Fiala & Delille 1992, Delille et al. 1995. However, in this study the maximal autotrophic biomass (corresponding to 42 mg chl a m -3 in December) was low relative to relevant published data. ...
The coastal sea ice in the vicinity of Dumont d'Urville station, Antarctica (66degrees 40' S, 140degrees01'E) supports a diverse microbial community. To investigate seasonal changes in bacterial, microalgal and protozoan biomass during the ice-coverage period, a survey was conducted on fast ice in the continental shelf of Terre Adelie. A reference station was sampled twice a month from April to December 1997. In April and May, during sea ice formation, the autotrophic biomass reached relatively high levels ranging from 400 to 800 mgC m(-3) in the subsurface ice. A second increase reaching 1500 mgC m(-3) in mid-December occurred in early summer in the bottom ice layer. Bacterial biomass ranged from < 10 mg C m(-3) in August and September to > 200 Mg C m(-3) in May. Maximal levels of bacterial biomass were detected during ice formation and just before the summer thaw. Total protozoan biomass increased from May to July. Maximum protozoan biomass (31.8 mgC Mm(3)) occurred in the surface ice layer in July. Except for during a short period (late May to early June), ciliates were dominant, accounting for 50 to 77% of the total protozoan biomass. During the ice-covered period, phototrophic biomass was always dominant. Microalgal biomass contributed on average 80.6% of total biomass whereas bacterial and protozoan biomass accounted for only 16.4 and 3%, respectively. Despite their low biomass, protozoa seem to play a major role in bacterial regulation.
The Antarctic marine ecosystem is one of the largest ecosystems on the planet. It is bound by the Antarctic continent to the south and by the Polar Front to the north. Physical, chemical, and biological properties are distinct to this system both by their absolute value as well as by their scale of variability. For example, low and relatively constant temperatures are characteristic of surface marine waters (from —1.84° and 2.5°C) (Hofmann et al. 1996). In contrast, solar radiation presents a large seasonal variability that reaches an extreme of 24h of light in summer and 24h of darkness in winter, south of the Antarctic polar circle (66.5° S). Similarly, a strong seasonal variability in sea ice coverage reaches maximum values in winter (July and August) and minimum in the fall (March), sweeping approximately half the Antarctic marine ecosystem and effectively doubling the surface of the Antarctic continent. Atmospheric circulation, a driving force on air temperatures and sea ice distribution, includes several cyclonic pressure systems that surround the continent, introducing winds, cloudiness, moisture, and heat into the marine environment and coastal regions in a scale of days to weeks.
A set of eight large (20 m 3 ) mesocosms were moored in Johnson's Dock (62839.5769S, 60822.4089W, Livingston Island, Antarctica) to experimentally generate a gradient of phytoplankton biomass and production in order to test the extent of coupling between bacteria (heterotrophic Bacteria and Archaea) and phytoplankton, as well as the role of bacterial losses to protist grazers. This was achieved by imposing four light levels (100%, 50%, 25%, and 10%) in the presence or absence of nutrient additions (0.1 mol NH4Cl, 0.1 mol F6Na2Si, and 0.01 mol KH2PO4 per day per mesocosm). The experimental treatments resulted in a broad range of chlorophyll a (Chl a) (0.31-93.5 mg Chl a L 21 ) and average primary production rates, while bacteria responded in a much narrower range of biomass (3-447 m gCL 21 ) and production (0.21- 15.71 m gCL 21 d 21 ). Results confirm that bacteria-chlorophyll and bacterial production-primary production relationships in the Southern Ocean differ from the typical relationships applicable to aquatic ecosystems elsewhere. Bacteria respond to phytoplankton blooms, but they respond so weakly that bacterial production represents a small percentage of primary production (1-10%). Although other mechanisms might also contribute to the weak bacterial response to phytoplankton blooms, we demonstrate that the reason for it is likely the tight control of bacterial populations by their predators. Protist grazers are able to sustain faster growth rates in the cold waters of the Southern Ocean than are bacteria, thereby preventing bacteria from responding to phytoplankton blooms more forcibly.
Hydrobiological conditions (light penetration, temperature, salinity, chlorophyll biomass at six depths and bacterioplankton abundance at the surface) were measured weekly for six years (1992–1997) at a station located in a coastal area of the Gulf of Guinea (Abidjan, Côte d'Ivoire). Nutrient concentrations completed the data set from December 1994. This coastal area is strongly influenced by a major upwelling (July–September) and by a minor upwelling (short cold events during January–February). Continental inputs induced by local rainfalls (May–June and October) and river floods (September–November) have also pronounced hydrological effects. SST varied from 20.6°C (August) to 30.7°C (May), while surface salinity showed an obvious annual cycle with a minimum of 30.12 psu in June and a maximum of 35.87 psu in September. Bacterial abundance and phytoplankton biomass show seasonal cycles, with simultaneous peaks noted during the main upwelling (maximum: 1.9 106 cell ml−1 and 5.6 μg l−1 respectively). Interannual fluctuations of upwelling intensity and of continental inputs explain the hydrological variability. Freshwater inputs are associated with oligotrophy, while upwellings contribute to the enrichment of the euphotic layer. As a consequence of the drought in the Sahel and of the decreasing rainfall on the coastal area, freshwater inputs are now considerably reduced, and the related impoverishment is less pronounced. At the opposite, the increasing duration of upwellings (and the importance of the short cold events) allows a higher primary productivity (and therefore a more active bacterial compartment). Combined, these two factors would explain the marked outburst of small pelagic fishes in this part of the Gulf of Guinea.
Bacterial biomass ranged from 3.159 X 10¹³ to 6.234 X 10¹³ cells m⁻² sea surface whilst phytoplankton biomass ranged from 8.5-298 mg chlorophyll a m⁻² (both integrated to 200 m depth). Net phytoplankton species composition resembled that found previously in this area. The ratio of bacterial- to phytoplankton-carbon increased with depth with a mean value of 9.32% (range 0.19-53.03%) for samples in the top 50 m of the water column but usually representing at least half of the microplankton biomass at depths >100 m. Correlation between bacterial and phytoplankton biomass was negative but not significant. Variation in total chlorophyll a, dominated by large-celled diatoms, probably would not affect bacterial biomass which would be more closely linked to that of picophytoplankton.-from Authors
The relationships of vertical profiles of phytoplankton photosynthesis to under-water light were studied at 23 stations in the South Scotia Sea and Bransfield Strait. On 3 occasions diurnal photosynthetic patterns were monitored. Chlorophyll-a concentrations varied by a factor of 16.5. Eighty per cent of the variations in light extinction could be explained by variations in chl-a concentration. Accordingly, the euphotic zone (1% surface light level) varied from 15 to 70 m. Photosynthetic profiles were studied in order to assess the production potential of Antarctic phytoplankton. The photosynthetic capacity (photosynthesis per chl-a at optimum light) and maximum quantum yield of photosynthesis (moles carbon dioxide assimilated per mole light quanta absorbed) on the average were smaller by a factor of 7 and 4, respectively, than in phytoplankton at lower latitudes. Diminished low-light photosynthesis suggests that in Antarctic waters temperature-controlled processes take over as rate-limiting steps in otherwise light-limited situations. The utilization efficiency of incident irradiance by phytoplankton at any level of chlorophyll concentration is diminished by both reductions in the photosynthetic capacity and lower light-limited quantum yields. By the combination of both effects, phytoplankton in Antarctic waters can utilize incident light only inefficiently even in situations where biomass accumulation is high.
Examines relationships between pelagic phytoplankton growth and environmental variables in polar seas with reference to the geographical and seasonal distribution of standing stock. Comments are made on the physiological ecology of Arctic and Antarctic phytoplankton, with attention drawn towards the effects of the light regime (the most significant factor, which includes intensity, duration and the submarine light gradient), nutrients and temperature. Photosynthetic rate per unit phytoplankton biomass in Antarctic waters is severely limited by thermodynamic effects on cellular enzyme systems.-P.J.Jarvis