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- Wikner, Johan, 1961-, et al.
(författare)
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Annual Study of Bacterioplankton Community Dynamics.
- 1991
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 36:7, s. 1313-1324
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial growth, abundance, and grazing were measured simultaneously during a full seasonal cycle in a temperate brackish water estuary, covering diel and seasonal variability. Growth of bacteria was balanced by bacterivory on an annual basis, and observed net change in bacterial numbers matched the net change calculated by a simple Lotka-Volterra equation lacking immigration or emigration terms. Bacterial growth was dependent on water temperature below 6-degrees-C, but other factors dominated at higher temperatures. The community clearance rate of the bacterivores was stringently regulated at 0.6 d-1, showing a linear functional response within the range of natural bacterial abundances recorded. Furthermore, bacterivores showed a threshold at 7 x 10(5) bacteria ml-1 when grazing ceased, suggesting that pelagic bacteria have a numerical refuge promoting coexistence with bacterivores in aquatic environments. The observed lack of timing between bacterial growth and grazing in spring allowed accumulation of bacterial cells, but grazing exceeded growth in winter. We inferred that the specific growth rate of the bacterial community and the community clearance rate of bacterivores together determined change in and abundance of bacterioplankton in the waters examined.
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- Wikner, Johan, 1961-, et al.
(författare)
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Periodic bacterivore activity balances bacterial-growth in the marine-environment
- 1990
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 35:2, s. 313-324
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Tidskriftsartikel (refereegranskat)abstract
- The grazing rate of pelagic bacteria was repeatedly determined during 36-h time-course experiments with the minicell recapture technique. Die1 variation in the rate of grazing occurred in all water masses investigated. Maximal rates reached 2 x lo5 cells ml-’ h-r, whereas minimal values were 20 times lower. Highest grazing rates were found during the day in most cases, but grazing could also dominate at night as found in one study. Die1 periodicity was mainly due to variation in the per-cell feeding rate of bacterivorous flagellates. Accumulation of the bacterial biomass into the l-3-pm size fraction was positively correlated with changes in bacterial grazing. The transfer efficiency to organisms z 10 pm was low. On average, the daily grazing rate equaled 60% of the bacterial standing stock, exceeding bacterial growth by a factor of 2.6, as estimated from [3H]thymidine incorporation.
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- Zweifel, Ulla-Li, et al.
(författare)
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DYNAMICS OF DISSOLVED ORGANIC-CARBON IN A COASTAL ECOSYSTEM
- 1995
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 40:2, s. 299-305
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Tidskriftsartikel (refereegranskat)abstract
- In the Bothnian Sea, there was a marked seasonal variation of dissolved organic C (DOC) in 1990-1992, with a large increase in DOC concentrations in summer at two stations. The accumulation of DOC at the coastal station persisted for 5 months, reaching peak values 24-31% above the mean winter value (288 mu M). At the offshore station DOC concentrations were elevated throughout the water column in July, reaching 14% above the mean winter value (291 mu M). The DOC concentration at the Coastal station was significantly correlated to water flow in an adjacent river, suggesting that the source of the summer DOC increase was largely explained by riverine input. Bioassays indicated that a large portion (22-99%) of the introduced DOC was degradable by bacteria after inorganic nutrients were added. A negative correlation between DOC and phosphate concentration was also found, suggesting that the system was P deficient in summer. The accumulation of DOC in summer was thus possibly caused by slow bacterial degradation due td phosphate deficiency and transient accumulation of refractory DOG. An annual C balance at the coastal station indicated an insufficient supply of C from phytoplankton production to support the C demand of the system; at the offshore station the budget was close to balanced. The results suggest that riverine DOC had a major impact on coastal DOC dynamics and that it was partly used in the microbial food web in the bay.
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