Distribution of heterotrophic nanoflagellates and their importance as the bacterial consumer in a eutrophic coastal seawater

Fukami, Kimio; Murata, Noriyuki; Morio, Yuuki; Nishijima, Toshitaka

doi:10.1007/bf02239045

Cited by 34 publications

(19 citation statements)

References 21 publications

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“…We emphasize, however, that at present there is no standard method to estimate the activities in sediment. Researchers for instance have measured the fluxes of oxygen and carbon dioxide 14) , the rates of nucleic acid synthesis 35,47) , and the extracellular hydrolytic activities 28,40) , to evaluate the heterotrophic processes in the sediment. Therefore, any comparisons with results from studies using other methods or model substrates for instance should be made with caution.…”

Section: Discussionmentioning

confidence: 99%

“…A description of the study site can be found in earlier publications 14,15,37) . In brief, the site is a semi-enclosed shallow water (depth~16-17 m) coastal ecosystem which witnesses only limited water exchange 15) , and experiences pronounced density stratification 14,37) during an annual cycle. Furthermore, the inlet contains a large number of fish rearing cages from which a considerable amount of nutrients is discharged leading to eutrophication of the inlet.…”

Section: Study Site and Sample Collectionmentioning

confidence: 99%

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Extracellular Proteolytic Activity in the Surface Sediment of a Eutrophic Inlet.

2001

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The potential aminopeptidase activity (APA) in surface sediment (0-1 cm), and important ecological factors of a eutrophicated inlet were monitored for one and a half years on a weekly to biweekly basis to elucidate the fluctuations in extracellular hydrolysis of protein during an annual cycle, and main regulating factors on an annual and/or a seasonal basis. APA was estimated in sediment slurry prepared with unamended bottom water, as the V max of the rate of the enzymatic hydrolysis of a coumarine derivative fluorophore at in situ temperatures. APA varied 5-6 fold during the study period with highest values (225-275 nmole AMC h -1 g -1 dry weight) during September-October or early June when the temperature was 22-28°C and dissolved oxygen concentrations (DO) (2-4 mg L -1 ) in overlying bottom water were high, and much lower values (ca. 50 nmoles AMC h -1 g -1 dry weight) in July-August or December-February. On an annual basis, APA correlated only marginally (p < 0.05; r = 0.25) with the protein content of the surface sediment and not at all with any other variables. However, it showed highly significant correlations (p < 0.001) with temperature (r = 0.81), and protein content (0.65) in mid December-early June, when temperatures were relatively low (ca. 12-22°C) and DO was abundant (ca. 2-6 mg L -1 ) in overlying bottom water.

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Section: Discussionmentioning

confidence: 99%

Section: Study Site and Sample Collectionmentioning

confidence: 99%

Extracellular Proteolytic Activity in the Surface Sediment of a Eutrophic Inlet.

2001

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“…1). The description of the site can teristically use high protein diets (McCaig et al 1999), be found elsewhere (Fukami et al 1991b(Fukami et al , 1996. In Hence, it is important to quantify their extracellular hyshort, near and around the sampling station, intensive drolysis in the recipient ecosystems, and also to know cage culture of yellow tail and red sea bream is widely the main environmental factors which regulate their practiced.…”

Section: Methodsmentioning

confidence: 99%

“…In some cases, it has even directly affected the farming by causing mass mortalities of cultivated animals (Johnsen et al 1993). 'Corresponding author: E-mail: fukami@cc.kochi-u.ac.jp In order to ensure clean coastal environments and sus-0 Inter-Research 2000 tainable farming, these allochthonous organic materihave also been reported (Fukami et al 1996). In the als must be decomposed and utilized by the microflora present paper, we describe fluctuations in the APA in or recycled within the recipient ecosystems.…”

Section: Introductionmentioning

confidence: 99%

Regulation of seasonal variability of aminopeptidase activities in surface and bottom waters of Uranouchi Inlet, Japan

Patel¹,

Fukami²,

Nishijima³

2000

Aquat. Microb. Ecol.

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The potential aminopeptidase activity (APA) vis-a-vis important ecological parameters of surface and bottom waters of Uranouchi Inlet (Japan), a semi-enclosed eutrophic coastal ecosystem, were studied on a weekly to biweekly basis from mid-August 1996 to early November 1997. The aim of this study was to investigate the main factors regulating the annual and seasonal dynamics of APA in the inlet. APA was estimated in short-term incubations as the V, , of the rate of enzymatic hydrolysis of a fluorophore 7-L-leucyl-4-methyl couomarinylarnide under conditions close to those of in situ. The water column structure at the study site changed considerably during the study period as the ecological parameters such as temperature, dissolved oxygen (DO), nutrient contents, and bacterial abundance exhibited pronounced seasonal stratification (May to September). When the water column was mixed (October to March), surface and bottom waters possessed similar APA . But when the water column became stratified, pronounced differences became apparent, with surface water showing considerably higher APA. On extreme days, surface water possessed as much as -20 times higher APA than that of bottom water. Thus, APA of surface water demonstrated strong seasonality and varied by almost 40-fold compared to that of bottom water, which varied only about 12-fold during the study period. Notably, bacterial abundances of both waters showed limited seasonality and varied only -3-fold during the same period. These results imply that changes in APA are not merely a function of bacterial abundance but rather more of per-cell activity. On an annual basis, APA in both waters were positively correlated (p < 0.001) with temperature and bacterial abundance, and negatively correlated with s M i t y (p c 0.001 for surface and p < 0.01 for bottom water) but were not correlated (p > 0.05) with DO, chlorophyll a (p < 0.05; only for surface water), inorganic or organic forms of nitrogen (DIN, DON) or inorganic phosphorous (DIP) contents. Furthermore, when the water column was mixed, APA correlated strongly with temperature (p < 0.001; r = 0.87), and marginally (p < 0.05) with DIN (r = 0.43) and DIP (r = 0.40) content but not with DO (p > 0.05) content. In contrast, when the water column became stratified, APA correlated only marginally with temperature (0.01 c p < 0.05; r = 0.33) but strongly with DO (p c 0.001; r = 0.73), and negatively (p c 0.001) with DIN (r = -0.61) and DIP (r = -0.70) content. DON content did not show any correlation (p > 0.05) with APA regardless of whether the water column was mixed or stratified. These correlations suggest that temperature played a critical role in regulating the APA when the water column was mixed (October to March), and DO or inorganic nutrient contents (May to September) when the water colun~n was stratified.

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“…In addition, in the last two decades, a new carbon pathway termed the "microbial loop" has been proposed (Azam et al 1983) and many studies have shown its importance in material flow (e.g. Fukami et al 1996). It is supposed whether organic carbon produced by phytoplankton goes into the grazing food chain or microbial loop depends on the physiology and/or community structure of the phytoplankton (Roman et al 1988, Levasseur et al 1996.…”

Section: Introductionmentioning

confidence: 99%

Response of lower trophic organisms to nutrient input and effects on carbon budget: a mesocosm experiment

Tsuda

Fukami

Kiyosawa³

et al. 2010

Plankton Benthos Res

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Abstract:The roles of heterotrophic organisms (microzooplankton, mesozooplankton, bacteria and heterotrophic nanoflagellates) were examined during a nutrient enrichment experiment using a mesocosm in Saanich Inlet, British Columbia, Canada. Grazing rates of microzooplankton, copepods, and Noctiluca scintillans were respectively estimated by the dilution method, from the egg production, and the apparent growth rate. The primary production increased by about 11 times during the initial 3 days, and the grazing rate by zooplankton also increased by 7.4 times. The primary production exceeded the grazing rate during the initial 5 days, after that, almost balanced rates were observed. Biomass peaks of bacteria and HNFs (heterotrophic nanoflagellates) were observed after the decline of the phytoplankton bloom. Bacterial production and HNF bacterivory gradually increased from the beginning to the end of the experiment. Microzooplankton consistently removed about half of the primary production. The contribution of microzooplankton to grazing was largest during the initial 7 days. Heterotrophic dinoflagellates were the most dominant component of the microzooplankton, but oligotrich ciliates showed the fastest growth response to phytoplankton production. Noctiluca scintillans became an important grazer after the bloom. Overall, the contribution of microzooplankton grazing was the largest of the processes through which phytoplankton were lost. Cell sinking was a minor component contributing to loss of phytoplankton. Thus, oligotrich ciliates and heterotrophic dinoflagellates were the most plausible organisms contributing to the steady state of phytoplankton concentrations.

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Distribution of heterotrophic nanoflagellates and their importance as the bacterial consumer in a eutrophic coastal seawater

Cited by 34 publications

References 21 publications

Extracellular Proteolytic Activity in the Surface Sediment of a Eutrophic Inlet.

Extracellular Proteolytic Activity in the Surface Sediment of a Eutrophic Inlet.

Regulation of seasonal variability of aminopeptidase activities in surface and bottom waters of Uranouchi Inlet, Japan

Response of lower trophic organisms to nutrient input and effects on carbon budget: a mesocosm experiment

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