A model for short-term control of the bacterioplankton by substrate and grazing

Heterotrophic bacterioplankton abundance, production, and specific growth rate in a salt‐marsh tidal creek were measured weekly from April 1991 to September 1992. During the same period, tidal and diel sampling studies were performed in May, June, and October 1991 and May and August 1992. Seasonal variability of bacterial abundance, production, and specific growth rate was regulated by temperature during nonsummer seasons when temperature was <20°C. During summer, bacterial variables were not limited by temperature. Daily variability of bacterial abundance, production, and specific growth rate was regulated interactively by tidal mixing, substrate supply, and temperature over several tidal cycles. Higher bacterial abundance, production, and specific growth rate observed at low tide indicated that bacterial growth rate in the tidal creek was higher than in the adjacent river waters. This pattern might be due to larger nutrient fluxes originating in the tidal creek. Occasionally, the tidal effect was overridden by temperature during study periods when temperature changed dramatically over several tidal cycles. Bacterial diel patterns in production and specific growth rate in the tidal creek occurred only when day‐night temperature differences exceeded 10°C, with maximal values during daytime. Short‐term temperature manipulation experiments suggested that diel patterns in bacterial production and specific growth rate were probably caused by temperature, not light intensity. Thus, temperature regulated both seasonal and diel variations in bacterial production.

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 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.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 211:63-76 (2001) - doi:10.3354/meps211063 Pico- and nanoplankton biomass and production in the two largest atoll lagoons of French Polynesia Christine Ferrier-Pagès*, Paola Furla Observatoire Océanologique Européen, Centre Scientifique de Monaco, Av. Saint Martin, 98000 Monaco *E-mail: ferrier@unice.fr ABSTRACT: Pico- and nanoplankton concentrations were measured in the lagoonal waters of the 2 largest atolls of French Polynesia (Fakarava and Rangiroa). Growth, production and grazing rates were estimated using diffusion chambers near the reef flat spillways and near the main channels of the atolls. The overall microbial biomass was dominated by picoplankton, with very high abundances of bacteria and cyanobacteria, these 2 groups representing each 20 to 50% of the total carbon. Nanoplankton (auto- and heterotrophic flagellates) constituted only 10 to 15% of the total biomass. Microbial concentrations were 1.5 to 3-fold lower near the reef flat spillways than near the channels. This suggests an important biomass production inside the lagoon. At Rangiroa, growth rates varied from 0.02 to 0.06 h-1 for bacteria and from 0.01 to 0.04 h-1 for the other groups (cyanobacteria, auto- and heterotrophic flagellates). At Fakarava, growth rates were in the same range except for the heterotrophic flagellates (0.05 to 0.17 h-1). Growth rates were significantly higher near the reef flat spillways than near the channels. More than 50% of both bacterial and cyanobacterial production was grazed by the higher trophic levels in both atolls. Bacterial production was enhanced by a nitrogen enrichment whereas production of cyanobacteria and flagellates was enhanced by both a nitrogen and a phosphorus enrichment. KEY WORDS: Atoll lagoon · Picoplankton · Nanoplankton · Growth · Nutrient limitation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 211. Online publication date: February 14, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

The growth rate and losses of bacterioplankton in the epilimnion of an oligo-mesotrophic reservoir were simultaneously estimated using three different methods for each process. Bacterial production was determined by means of the tritiated thymidine incorporation method, the dialysis bag method and the dilution method, while bacterial mortality was assessed with the dilution method, the disappearance of thymidine-labeled natural cells and ingestion of fluorescent bacterial tracers by heterotrophic flagellates. The different methods used to estimate bacterial growth rates yielded similar results. On the other hand, the mortality rates obtained with the dilution method were significantly lower than those obtained with the use of thymidine-labeled natural cells. The bacterial ingestion rate by flagellates accounted on average for 39% of total bacterial mortality estimated by the dilution method, but this value fell to 5% when the total mortality was measured by the thymidine-labeling method. Bacterial abundance and production varied in opposite phase to flagellate abundance and the various bacterial mortality rates. All this points to the critical importance of methodological aspects in the elaboration of quantitative models of matter and energy flows over the time through microbial trophic networks in aquatic systems, and highlights the role of bacterioplankton as a source of carbon for higher trophic levels in the studied system.

Seasonal variations in abundance of heterotrophic bacteria, small (1-8 µm) heterotro- phic nanoflagellates (HNF), and ciliates, as well as bacterial production (BP) and bacterivory (PB) rates were investigated from May 1998 to May 1999 in the lower Urdaibai estuary (Bay of Biscay). Abundances ranged from 2.6 × 10 8 to 1.3 × 10 9 cells l -1 , 0.65 × 10 6 to 3.00 × 10 6 cells l -1 , and 12 to 436 cells l -1 for bacteria, HNF and ciliates, respectively. BP varied between 0.9 and 18.5 × 10 8 cells l -1 d -1 . Bacteria seemed to be more limited by food supply than by temperature. The major bacterivores were small HNF, but they could not satisfy their carbon demand only through bacterivory. Bacterivory rate per small HNF varied between 2.7 and 28.2 bacteria flagellate -1 h -1 . This rate showed seasonal vari- ations and was higher during late winter/early spring than during summer/early autumn. This pat- tern is probably due to the greater dependence of small HNF on bacteria during late winter/early spring, when the availability of food sources other than bacteria, e.g. autotrophic picoplankton, was low. This led to seasonal variations in the degree of grazing control on the bacterial standing stock, this control being tighter during late winter/early spring. Bacterivory rate was substantially higher than BP in many months, i.e. bacteria showed a negative growth, and this was paralleled by reduc- tion in bacterial abundance. The relationship between log bacterial abundance and log small HNF abundance suggested that small HNF were largely under a substrate supply (bottom-up) control.

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 25:31-42 (2001) - doi:10.3354/ame025031 Uncoupling of bacterial production and flagellate grazing in aquatic sediments: a case study from an intertidal flat Ilse Hamels*, Koenraad Muylaert, Griet Casteleyn, Wim Vyverman Protistology and Aquatic Ecology Section, Department of Biology, University of Gent, K.L. Ledeganckstraat 35, 9000 Gent, Belgium *E-mail: ilse.hamels@rug.ac.be ABSTRACT: In contrast to planktonic ecosystems, the fate of bacterial production in aquatic sediments is still largely unclear. In this study, we identified the factors regulating the impact of flagellate grazing on benthic bacterial production for a sandy and a silty intertidal sediment. Flagellate grazing rates were estimated using fluorescently labelled sediment to prevent disturbance of in situ bacterial density and community composition and to account for grazing on attached bacteria. Since flagellate cell size was quite diverse, the grazing rates were determined for 4 size classes. Bacterial production was measured simultaneously with grazing estimates. Bacterial density and production increased with decreasing median grain size of the sediment. Bacterial production was strongly related to the chlorophyll a content of the sediment, indicating resource control of bacterial production. In contrast to bacteria, flagellate biomass decreased with decreasing median grain size of the sediment. Pairwise comparison of grazing rates between the 2 sites showed that grazing rates were significantly higher at the sandy site. This suggests that the effect of sediment composition on flagellate biomass may be mediated by an influence of sediment characteristics on flagellate ingestion rates. The negative relation of bacterial production and the positive relation of flagellate biomass and grazing rates with median grain size resulted in a significant positive relation between the impact of flagellate grazing on bacterial production and the median grain size of the sediment. These results amount to an uncoupling of flagellate grazing and bacterial production in fine sediments. Our results as well as results from previous studies suggest that grazing by flagellates is not an important fate of bacterial production in aquatic sediments, except for sandy sediments during periods of low bacterial production. KEY WORDS: Bacterivory · Heterotrophic flagellates · Grazing rates · Bacterial production · Intertidal sediments Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 25, No. 1. Online publication date: August 10, 2001 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2001 Inter-Research.

Heterotrophic bacterial production rates in soils on inland nunataks (rocky outcrops in the glacial ice sheet) in western Dronning Maud Land, Antarctica, were investigated by field and laboratory experiments using 3H-thymidine (3H-TdR) and 3H-leucine (3H-Leu) incorporation. Bacterial densities and productivities, and nutrient and physical parameters of soils from four different habitats were compared: soil from beneath moss beds, soil from the nests of the snow petrel (Pagodroma nivea), exposed unvegetated soil (polygon soil) 5 m away from nests, and exposed polygon soil on nunataks without the nests of breeding birds. Organic content, and nitrogen and carbon concentrations were significantly higher (ANOVA, P 0.05) from polygon soils from nunataks with breeding birds. Exposed polygon soils reached the highest midsummer midday temperatures (>20°C), while moss and nest soils remained much cooler. However, nest and moss soils were relatively thermally stable, compared to widely fluctuating exposed polygon soils. Soils from nests exhibited significantly (P < 0.05) higher rates of bacterial production than did any other habitat (32.3 ± 42.2 and 18.8 ± 13.8 cells × 106 gDW−1 h−1, for 3H-thymidine and 3H-leucine incorporation, respectively), whereas productivity in moss soils (9.5 ± 5.6 and 7.9 ± 1.5 cells × 106 gDW−1 h−1, for 3H-thymidine and 3H-leucine incorporation, respectively) was more than twofold greater than in either polygon soil habitat. Soils in nests and moss beds thus represent bacterial ``hotspots'' in an extensive matrix of exposed polygon soils, supporting denser bacterial populations and enhanced bacterial productivity. Whereas increased bacterial productivity in nest soils may be attributed to enhanced soil nutrient levels, productivity in moss soils appears to be limited by nutrients, and in polygon soils is further dampened by desiccation and relatively large daily temperature fluctuations. Stepwise multiple regression analysis revealed no correlation between bacterial productivity and physical factors measured. Weak but significant correlations were obtained between bacterial productivity and nutrient availability. This suggests that during the most favorable conditions in midsummer, bacterial growth is limited primarily by resource availability. However, water availability and temperature are likely to play important but intermittent regulatory roles.

Rates of primary and bacterial secondary production in Lake Arlington, Texas, were determined. The lake is a warm (annual temperature range, 7 to 32 degrees C), shallow, monomictic reservoir with limited macrophyte development in the littoral zone. Samples were collected from six depths within the photic zone from a site located over the deepest portion of the lake. Primary production and bacterial production were calculated from NaHCO(3) and [methyl-H]thymidine incorporation, respectively. Peak instantaneous production ranged between 14.8 and 220.5 mug of C liter h. There were two distinct periods of high rates of production. From May through July, production near the metalimnion exceeded 100 mug of C liter h. During holomixis, production throughout the water column was in excess of 100 mug of C liter h and above 150 mug of C liter h near the surface. Annual areal primary production was 588 g of C m. Bacterial production was markedly seasonal. Growth rates during late fall through spring were typically around 0.002 h, and production rates were typically 5 mug of C liter h. Growth rates were higher during warmer parts of the year and reached 0.03 h by August. The maximum instantaneous rate of bacterial production was approximately 45 mug of C liter h. Annual areal bacterial production was 125 g of C m. Temporal and spatial distributions of bacterial numbers and activities coincided with temporal and spatial distributions of primary production. Areal primary and bacterial secondary production were highly correlated (r = 0.77, n = 15, P < 0.002).

Copper effects on bacterial activity of estuarine silty sediments

Vertical patterns of bacterial densities, productivity and specific growth rates in coastal muds, quartz sands and muddy sands of the central Great Barrier Reef lagoon were examined in summer (February) and autumn (May) 1988. Variations in these parameters with station location, sediment depth and season were complex, exhibiting significant main and interaction effects in most instances. Some trends were apparent despite the large and complex variations. Bacterial densities did not vary seasonally, ranging from 2.9 to 38.1×109 cells g-1 dry wt, averaged over sediment depth (0 to 20 cm) and seasons. Trend analysis revealed that densities decreased with increasing sediment depth. Bacterial production (tritiated thymidine incorporation into DNA) was high, ranging from 0.4 to 5.7 gCm-2 d-1 (integrated over 10 cm depth), as were specific growth rates (grand mean, μ=0.25 d-1; range=0.004 to 1.3 d-1). Both were generally higher in summer than in autumn. Vertical profiles of productivity and specific growth rates revealed actively growing bacterial assemblages down to 20 cm depth. Factors which may account for these very abundant and productive communities are: (1) subsurface accumulations of detritus exported from adjacent mangrove forests, and (2) physical disturbance from tidal scouring and severe climate (e.g. cyclones, wet-season floods). Disturbance events occur frequently enough to inhibit the development of highly sulphidic conditions, but stimulate production of bacterial types (aerobes, fermenters) capable of incorporating labelled thymidine into their DNA.

Seasonal Evolution of Microplanktonic Communities in the Estuarine Front Ecosystem of the Rhône River Plume (North-western Mediterranean Sea)

As leaves enter woodland streams, they are colonized by both fungi and bacteria. To determine the contribution of each of these microbial groups to the decomposition process, comparisons of fungal and bacterial production are needed. Recently, a new method for estimating fungal production based on rates of [(sup14)C]acetate incorporation into ergosterol was described. Bacterial production in environmental samples has been determined from rates of [(sup3)H]leucine incorporation into protein. In this study, we evaluated conditions necessary to use these methods for estimating fungal and bacterial production associated with leaves decomposing in a stream. During incubation of leaf disks with radiolabeled substrates, aeration increased rates of fungal incorporation but decreased bacterial production. Incorporation of both radiolabeled substrates by microorganisms associated with leaf litter was linear over the time periods examined (2 h for bacteria and 4 h for fungi). Incorporation of radiolabeled substrates present at different concentrations indicated that 400 nM leucine and 5 mM acetate maximized uptake for bacteria and fungi, respectively. Growth rates and rates of acetate incorporation into ergosterol followed similar patterns when fungi were grown on leaf disks in the laboratory. Three species of stream fungi exhibited similar ratios of rates of biomass increase to rates of acetate incorporation into ergosterol, with a mean of 19.3 (mu)g of biomass per nmol of acetate incorporated. Both bacterial and fungal production increased exponentially with increasing temperature. In the stream that we examined, fungal carbon production was 11 to 26 times greater than bacterial carbon production on leaves colonized for 21 days.

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 20:39-48 (1999) - doi:10.3354/ame020039 Consequences of solar radiation on bacterial secondary production and growth rates in subtropical coastal water (Atlantic Coral Reef off Belize, Central America) Ryszard J. Chróst1,*, Maria A. Faust2 1Microbial Ecology Department, University of Warsaw, Karowa 18, 00-324 Warsaw 64, Poland 2Department of Botany, National Museum of Natural History, Smithsonian Institution, Suitland, Maryland 20746, USA *E-mail: chrost@plearn.edu.pl ABSTRACT: This study reports the effects of natural solar radiation on production and growth rates of bacterial assemblages in coastal surface water of the Atlantic Barrier Coral Reef off Belize, Central America. Bacterial production rates measured in the late afternoon were significantly lower than rates measured in the morning. There were also significant differences in the specific growth rates of bacterial assemblages between water samples: bacteria grew faster, i.e. displayed shorter doubling times, in the early morning. Bioassay experiments showed a significant increase in rates of bacterial secondary production in water samples exposed in situ to ambient solar radiation at the water surface. There was also a pronounced increase in the growth rates and cell volumes of bacteria grown in sunlight-irradiated water samples. We suggest that enhanced metabolism of bacteria grown in water samples that were previously exposed to solar radiation was due mainly to photodegradation of dissolved organic matter and subsequent enrichment of water with easily utilizable substrates. The results of these studies indicate that solar radiation can directly alter bacterial production and growth over diel cycles in subtropical waters. These physico-chemical and biological interactions between solar radiation and heterotrophic bacteria in subtropical coastal water may have important biogeochemical implications at both the ecosystem and global levels. KEY WORDS: Bacterial production · Bacterial growth rates · Solar radiation · Subtropical coastal waters Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 20, No. 1. Publication date: November 30, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

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