Bacterial biomass and production in pack ice of Antarctic marginal ice edge zones

The temporal variation of ice primary and bacterial production along with ice algal, bacterial and heterotrophic flagellate biomass were studied at a coastal station in the northern Baltic Sea throughout the ice-covered period of 1996 (January to April). Ice core samples were taken every week and analyzed for abundance and production of different microorganisms. In addition, physical and chemical parameters were measured. The ice algae were Limited by light during the first 3 mo of the study. The algal production showed a peak in the middle of April, which coincided with a marked increase in light availability. Shortly after that, the system became phosphorus depleted and primary production decreased rapidly. Bacterial biomass and production rates were relatively low and stable before the ice algal bloom. After the ice algal bloom, bacterial production increased rapidly, while the biomass remained low. The growth rate of small heterotrophic flagellates (<l0 pm), calculated from increase in biomass, was more than 1 order of magnitude higher than the bacterial production rate following the ice algal bloom. Thus, small heterotrophic flagellates were using food sources other than bacteria for growth after the ice algal bloom. On an annual basis, the ice algal and bacterial production accounted for < l % and <0.1% respectively of the total production (ice + pelagic) due to a short ice-covered season. During the ice-covered season, however, the ice algae accounted tor 10% of the total algal production, whlle ice bacterial production was 0.2 % of the total bacterial produckon.

Bacterial response to the rare event of solid ice cover in the western Baltic Sea (Kiel Bight) was investigated from February to March 1996. Samples (ice cores, brine and water) were taken at a shallow, near-shore station at irregular time intervals. Bacterial abundance, biomass and production were measured in brine and the underlying water as were the concentrations of NO3, NO2, NH4, PO4 and SiO4. Vertical distributions of bacterial abundance, biomass, morphotypes and size classes and chlorophyll a and nutrients were investigated within sea ice. A bacterial growth experiment with brine bacteria was carried out to measure bacterial carbon production via total incorporation of [3H]thymidine (TTI) and [3H]leucine (TLI). During February the abundance, biomass and production of bacteria within brine exceeded values from under-ice water, whereas the opposite was observed in March. High NO3 and NH4 concentrations in ice and under-ice water of up to 112 µM and 55 µM, respectively, resulted in N:P ratios of 18 to 330. Algae and bacteria were considered to benefit from that nutrient supply. For bacteria this was supported by TTI and particularly high TLI rates during the ice situation, with TLI:TTI ratios of 25 to 213. The high TLI rates were due to a large degree of unspecific labeling by leucine and characterised the bacteria during winter 1996 as extremely active. Bacterial production (based on TTI) rose in water from 0.021 µg Cl-1 h-1 at the beginning to 0.909 µg Cl-1 h-1 at the end of the investigation, and in brine from 0.122 to 0.235 µg Cl-1 h-1. Abundance of bacteria in brine increased from 1.7 x 106 cells ml-1 initially to 2.8 x 106 cells ml-1 in March. The average cell volume of these bacteria was 0.2 µm3 whereas the bacteria in water reached only 0.08 µm3. The bacterial assemblage in the ice was dominated by large rods and in the water by small rods and cocci. Bacterivorous activity within sea ice was assumed to be reduced due to the specific vertical distribution of the different bacterial size classes. This was further supported by a good correlation between the development of the bacterial standing stock and the potential biomass, in sea ice as well as in the underlying water, calculated from generation times towards the end of the investigation. Low grazing pressure, high standing stocks of algae and sufficient substrate supply accounted for bacterial biomass within the ice and the underlying water that exceeded that from former winters by far. A comparison with Arctic and Antarctic sites demonstrated that the bacterial community within the sea ice showed many similarities to those found in sea ice of polar regions.

The seasonal dynamics and distribution of bacteria and bacterial activity on eelgrass leaves were followed at a shallow-water site in the Roskilde Fjord, Denmark. Eelgrass leaves were sites of highly active bacterial communities exhibiting distinct distribution patterns with increasing bacterial abundance and production with increasing leaf age and from base to tip of individual leaves. High bacterial production and very high specific growth rates (seasonal mean 0.30 h -1 ) suggest a strong coupling between attached bacterial communities and plant primary production. Incorporation rates of 14 C-leucine and 3 H-thymidine were significantly correlated but the ratio between bacterial production based on leucine and thymidine increased with increasing leaf age and from leaf base to leaf tip, indicating a higher protein synthesis compared to DNA synthesis with increasing biofilm age. Bacterial biomass production was very high compared to the standing stock of bacteria and it was concluded that close to 100% of the bacterial biomass produced on the leaves was lost on a daily basis. Moreover, bacterial specific growth rates corresponded to turnover times of 1 to a few hours on most occasions and did not differ between leaves of different ages or at different locations on the leaves. Such high growth rates can only occur in a very rich environment, where the standing stock of biomass is kept low and thus prevents resource competition.

Seasonal and spatial patterns of heterotrophic bacterial production, respiration, and biomass in the subarctic NE Pacific

Heterotrophic bacteria influence the carbon export and consequently the efficiency of the biological carbon pump through the remineralization of organic matter. Bacterial remineralization was investigated during the SAZ-Sense cruise (January–February 2007) in the Subantarctic (SAZ) and Polar Front Zones (PFZ) of the Southern Ocean south of Tasmania, by combining bacterial biomass (BB) and bacterial production (BP) measurements in the epipelagic (0–100 m) and mesopelagic (100–700 m) water column. Bacterial carbon demand (BCD) was assessed using different conversion factors and growth efficiencies and was confronted to primary production and carbon export flux estimates. Surface layer bacterial biomass and production were higher in SAZ waters east of Tasmania (SAZ-East) compared to SAZ waters west of Tasmania (SAZ-West), while values at the PF were similar to those for the SAZ-West. At the PF, subsurface maximum values of bacterial production were observed. Bacterial parameters followed chl a and dissolved organic carbon distributions. Bacterial abundance, biomass and production drastically decreased below 100–200 m. However, depth-integrated biomass and activity rates revealed that the mesopelagic zone contributed significantly to the upper 700 m water column stocks (41–68% for BB) and rates (10–74% for BP). Highest and lowest contributions of mesopelagic BP to epi-plus mesopelagic water column BP were observed at the PF and in the SAZ-East, respectively. Results show that the SAZ-East region had a poor carbon sequestration efficiency compared to the SAZ-West and the PFZ. Despite some uncertainties in carbon flux estimations and discrepancies between methods the present study highlights the importance of studying bacterial dynamics in the twilight zone because of their significant role in shaping the carbon fluxes through the water column.

Bacterial abundance, biomass and production during spring blooms in the northern Barents Sea

Bacterial carbon demand, an important component of ecosystem dynamics in polar waters and sea ice, is a function of both bacterial production (BP) and respiration (BR). BP has been found to be generally higher in sea ice than underlying waters, but rates of BR and bacterial growth efficiency (BGE) are poorly characterized in sea ice. Using melted ice core incubations, community respiration (CR), BP, and bacterial abundance (BA) were studied in sea ice and at the ice–water interface (IWI) in the Western Canadian Arctic during the spring and summer 2008. CR was converted to BR empirically. BP increased over the season and was on average 22 times higher in sea ice as compared with the IWI. Rates in ice samples were highly variable ranging from 0.2 to 18.3 μg C l−1 d−1. BR was also higher in ice and on average ~10 times higher than BP but was less variable ranging from 2.39 to 22.5 μg C l−1 d−1. Given the high variability in BP and the relatively more stable rates of BR, BP was the main driver of estimated BGE (r 2 = 0.97, P < 0.0001). We conclude that microbial respiration can consume a significant proportion of primary production in sea ice and may play an important role in biogenic CO2 fluxes between the sea ice and atmosphere.

We investigated the dynamics of heterotrophic bacteria in the coastal western Antarctic Peninsula (WAP), using decadal (2002-2014) time series of two bacterial variables, bacterial production (BP) via 3H-leucine incorporation rates and bacterial biomass (BB) via bacterial abundance, collected at Palmer Antarctica Long Term Ecological Research (LTER) Station B (64.8°S, 64.1°W) over a full austral growing season (October-March). Strong seasonal and interannual variability in the degree of bacterial coupling with phytoplankton processes were observed with varying lags. On average, BP was only 4% of primary production (PP), consistent with low BP:PP ratios observed in polar waters. BP was more strongly correlated with chlorophyll (Chl), than with PP, implying that bacteria feed on DOC produced from a variety of trophic levels (e.g. zooplankton sloppy feeding and excretion) as well as directly on phytoplankton-derived DOC. The degree of bottom-up control on bacterial abundance was moderate and relatively consistent across entire growing seasons, suggesting that bacteria in the coastal WAP are under consistent DOC limitation. Temperature also influenced BP rates, though its effect was weaker than DOC. We established generalized linear models (GLMs) for monthly composites of BP and BB via stepwise regression to explore a set of physical and biogeochemical predictors. Physically, high BP and large BB were shaped by a stratified water-column, similar to forcing mechanisms favoring phytoplankton blooms, but high sea surface temperature (SST) also significantly promoted bacterial processes. High BP and large BB were influenced by high PP and bulk DOC concentrations. Based on these findings, we suggest an increasingly important role of marine heterotrophic bacteria in the coastal WAP food-web as climate change introduces a more favorable environmental setting for promoting BP, with increased DOC from retreating glaciers, a more stabilized upper water-column from ice-melt, and a baseline shift of water temperature due to more frequent delivery of warming Upper Circumpolar Deep Water (UCDW) onto the WAP shelf.

Antarctic sea-ice bacterial community composition and dynamics in various developmental stages were investigated during the austral winter in 2013. Thick snow cover likely insulated the ice, leading to high (<4 μg l-1) chlorophyll-a (chl-a) concentrations and consequent bacterial production. Typical sea-ice bacterial genera, for example, Octadecabacter, Polaribacter and Glaciecola, often abundant in spring and summer during the sea-ice algal bloom, predominated in the communities. The variability in bacterial community composition in the different ice types was mainly explained by the chl-a concentrations, suggesting that as in spring and summer sea ice, the sea-ice bacteria and algae may also be coupled during the Antarctic winter. Coupling between the bacterial community and sea-ice algae was further supported by significant correlations between bacterial abundance and production with chl-a. In addition, sulphate-reducing bacteria (for example, Desulforhopalus) together with odour of H2S were observed in thick, apparently anoxic ice, suggesting that the development of the anaerobic bacterial community may occur in sea ice under suitable conditions. In all, the results show that bacterial community in Antarctic sea ice can stay active throughout the winter period and thus possible future warming of sea ice and consequent increase in bacterial production may lead to changes in bacteria-mediated processes in the Antarctic sea-ice zone.

Bacterial abundance, biomass and production rates were determined at 3 depths (5, 10 & 15 m) in the water column above a Mediterranean seagrass bed in the Gulf of Calvi (west coast of Corsica, France) from 1988 to 1990. We used dialysis bags for in s ~ t u incubation of 2 pm prefiltered seawater sampled from the respective depths to determine bactenal growth parameters and conducted lightand dark-bottle incubations to estimate planktonic primary production by O2 measurements. Bacterial density and biomass was subject to marked seasonal changes. Bacterial density varied clearly over the seasons and between the 3 depths, with maximum values being recorded in Aug and Oct 1988 at the 10 and 15 m depths. Differences in bacterial biomass and density patterns were mainly attributed to changes of abundance and biovolume of rod-shaped bacteria. Highest carbon values were recorded during the summer months in 1989 and 1990 at the 3 depths and ranged from 32 to 65 pg C I-' Bacterial growth rates were closely correlated to temperature, with highest specific growth rates (0.075 to 0.125 h-') found in summer, when chlorophyll a concentrations were at a minimum during this season. Dur~ng Jan and Feb 1989 and 1990, when chl a concentrations were at a maximum, bacterial growth rates were below 0.001 h-' Doubling times (g) ranged from 5.2 to 23 h in summer, being lowest at the 5 m depth. Highest g values were recorded in Jan 1989 at 10 m (259 h). Dunng this period we observed an increase bacterial numbers within the dialysis bags, but a decrease in biovolume of the 4 morphotypes. We hypothesize that the observed growth strategy is necessary for bacteria to resist starvation and to obtain a competitive advantage for nutrient scavanging under oligotrophic conditions. In Jan, bacterial production corresponded to 7.6 % of gross primary production. In summer, bacterial production ranged from 18.5 to 48.4 % of gross primary production. Carbon requirements of the bacterial population in the water column were discussed in view of various carbon conversion efficiencies. The range of our bacterial production values is compared with values from other systems and seen in the context of the n~ethodological approaches.

The Southern Ocean is believed to be unproductive during winter due pnncipally to low irradiance.On the 1985 Wintercruise of the R N Polar Duke, considerable microbial blomass and rates of primary produchon and bactenal production were found in sea ice up to 1.79 m thick.Microbial activity associated with sea ice was equal to that found in several meters of underlying seawater.Downwelling irradiance was adequate for net production near the surface of ice-free water and in sea ice.Approximately 40 % of the newly fixed carbon incorporated by ice microalgae was assimilated into protein, suggesting that net growth was taking place without nutrient limitation.We propose that annual estimates of primary production should be revised upward by as much as 25 % to account for this unexpected productivity during late winter in the Southern Ocean.In addition, sea ice should be viewed as a concentrated source of microalgal carbon for grazers such as krill during late winter when phytoplankton in the water column are scarce.In situ observations by divers suggest that sea ice may also serve as an important nursery ground for larval knll during this time of year.We conclude that both the quantity of sea ice associated production and seasonal timing of this production are important factors in Antarctic trophodynamics.

Benthic bacterial production and biomass were measured at 16 stations in the North Sea covering a wide range of sediment types from the Southern Bight and the English coast to the Skagerrak. Stations were sampled in August 1991 and February 1992. The best predictor for summer/winter and spatial variations in benthic bacterial production in North Sea sediments was temperature. In winter the ranges in temperature were too small to account for the spatial variations in benthic bacterial production. The direct effect of temperature alone on bacterial production could not explain the variations. The apparent Q10-values derived from the relations between bacterial growth and temperature exceeded the range in Q10-values generally accepted for bacterial growth (between 2 and 3). Temperature was assumed to covary closely with substrate availability for bacteria. Due to its significant seasonality phytopigment content of the sediment (chlorophyll a and pheopigment) was found to be a better indicator of substrate availability than sediment organic matter, which did not demonstrate seasonality. Temperature and phytopigment accounted for up to 88% of the seasonal and spatial variations in bacterial production. The significant relations between bacterial production and biomass in summer coinciding with significant relations between bacterial biomass and phytopigments suggest that variations in phytopigments in the sediment may be indicators of the variability of labile components regulating bacterial production in sediments.

Seasonal and spatial variations in bacterial abundance, biomass and production in a recently flooded reservoir were followed for 2 consecutive years, in conjunction with phytoplankton biomass (chlorophyll a) and activity (primary production). Between the 2 years of the study, the mean value of primary production remained constant, while those of the chlorophyll a concentration, bacterial abundance (BA), bacterial biomass (BB) and bacterial production (BP) decreased. The observed trends of the bacterial variables were linked to changes in the relative importance of allochthonous dissolved organic matter. Moreover, this factor would explain discrepancies observed between the slope of the model II regression equations established from results of the present study and those of the predictive models from the literature, relating to bacterial and phytoplankton variables. An estimate of the carbon budget indicated that 22 and 5% of the ambient primary production in the Sep Reservoir might be channeled through the microbial loop via BP during the 1st and 2nd year of the study, respectively. We conclude that heterotrophic BP in the Sep Reservoir may, on occasion, represent a significant source of carbon for higher order consumers.

We report on investigations of bacterioplankton growth dynamics and carbon utilization in the full water column of the Ross Sea, Antarctica carried out on six cruises in 1994–1997, using epifluorescence microscopy, thymidine and leucine incorporation to estimate bacterial abundance and production, respectively. The Ross Sea experienced a bacterial bloom with an amplitude equaling similar blooms observed in the North Atlantic and North Pacific, reaching 3 � 10 9 cells l � 1 or 35 mmol C m � 2 in late January. Increases in bacterial biomass were driven both by increases in abundance and in cell volume. Cell volumes ranged from 0.03mm 3 cell � 1 in early spring to over 0.15mm 3 cell � 1 in midsummer. Larger cells were associated with faster division rates. Bacterial growth rates ranged 0.02–0.3 divisions d � 1 , equal to rates at lower latitudes. Bacterial biomass accumulated steadily in the upper water column at a net rate of 0.03 d � 1 . While there is clear evidence of a bacterial bloom in the Ross Sea, equal to bacterioplankton blooms observed in other oceanic systems, the magnitude of bacterial response relative to the phytoplankton bloom was modest. For example, euphotic zone bacterial production (BP) rates were equivalent to 1–10% of particulate primary production (PP) except in April 1997 when PP was very low and BP : PP was sometimes >1. BP integrated over the upper 300 m was a more substantial fraction of the overlying PP than BP in the euphotic zone alone, with bacterial carbon demand in the upper 300 m about 30% of the seasonal PP. There was significant seasonal variation of bacterial biomass below the euphotic zone, indicating dynamic bacterial growth in the lower layer, and a supply of labile organic matter for bacteria. Bacterial metabolism is apparently limited by DOC flux in the upper layer. There is little evidence of temperature limitation, independent of substrate concentration. The relatively small diagenesis of phytoplankton biomass in the

Seasonal and interannual trends in heterotrophic bacterial processes between 1995 and 1999 in the subarctic NE Pacific