Importance of bacterivory by pigmented and heterotrophic nanoflagellates during the warm season in a subtropical western Pacific coastal ecosystem

Tsai, An‐Yi; Gong, Gwo‐Ching; Sanders, Robert W.; Chen, Wei‐Hung; Chao, Chien-Fu; Chiang, Kuo‐Ping

doi:10.3354/ame01470

Cited by 51 publications

(45 citation statements)

References 63 publications

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“…Through cell lysis, bacterial biomass is converted to dissolved organic carbon, hence forcing the food web towards a more regenerative pathway (Wilhelm and Suttle, 1999). Our results substantiate earlier studies suggesting that nanoflagellates play an important role in bacterial carbon transfer to higher levels of the food web at this study site during summer (Tsai et al, 2011). However, bacterial production was not balanced by nanoflagellate grazing and viral lysis between June and August (33-68 % of bacterial production) (Fig.…”

Section: Discussionsupporting

confidence: 82%

“…Previous estimates of clearance rates of bacteria have been on the order of 10 −3 µL cell −1 h −1 for < 5 µm nanoflagellates and 10 −2 µL cell −1 h −1 for ciliates (Sherr et al, 1989), However, ciliate numbers are so low (∼ 1 cell mL −1 ) (Chen, 2003), thus resulting in ciliate grazing much lower than nanoflagellate grazing throughout observation period. Furthermore, Tsai et al (2011) also reported that the grazing impact by PNF was 20 times higher than that of ciliates at our study site during summer. Thus, the potential effect of nanoflagellate predation on the removal of picoplankton in our study appears to be substantial.…”

Section: Discussionmentioning

confidence: 81%

“…Until now, studies in the coastal ecosystem of subtropical western Pacific environment have mainly focused on bacterial mortality due to nanoflagellate grazing (Tsai et al, 2005(Tsai et al, , 2008(Tsai et al, , 2011. The contribution of viruses to bacterial mortality is still poorly understood.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal variations of virus- and nanoflagellate-mediated mortality of heterotrophic bacteria in the coastal ecosystem of subtropical western Pacific

2013

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Since viral lysis and nanoflagellate grazing differ in their impact on the aquatic food web, it is important to assess the relative importance of both bacterial mortality factors. In this study, an adapted version of the modified dilution method was applied to simultaneously estimate the impact of both virus and nanoflagellate grazing on the mortality of heterotrophic bacteria. A series of experiments was conducted monthly from April to December 2011 and April to October 2012. The growth rates of bacteria we measured ranged from 0.078 h⁻¹ (April 2011) to 0.42 h⁻¹ (September 2011), indicating that temperature can be important in controlling the seasonal variations of bacterial growth. Furthermore, it appeared that seasonal changes in nanoflagellate grazing and viral lysis could account for 34% to 68% and 13% to 138% of the daily removal of bacterial production, respectively. We suggest that nanoflagellate grazing might play a key role in controlling bacterial biomass and might exceed the impact of viral lysis during the summer period (July to August) because of the higher abundance of nanoflagellates at that time. Viral lysis, on the other hand, was identified as the main cause of bacterial mortality between September and December. Based on these findings in this study, the seasonal variations in bacterial abundance we observed can be explained by a scenario in which both growth rates and loss rates (grazing + viral lysis) influence the dynamics of the bacteria community

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Section: Discussionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 81%

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Seasonal variations of virus- and nanoflagellate-mediated mortality of heterotrophic bacteria in the coastal ecosystem of subtropical western Pacific

2013

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“…At most, they were divided into different cell size categories (Zubkov et al, 2001;Chan et al, 2009;Tsai et al, 2011) while very few studies have attempted to discriminate them by taxonomic affiliation (but see Havskum and Riemann, 1996). This is essentially because of the difficulty of determining the taxonomic identity of tiny organisms and simultaneously estimate their in situ grazing rates.…”

Section: Introductionmentioning

confidence: 99%

Mixotrophic haptophytes are key bacterial grazers in oligotrophic coastal waters

et al. 2013

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Grazing rate estimates indicate that approximately half of the bacterivory in oligotrophic oceans is due to mixotrophic flagellates (MFs). However, most estimations have considered algae as a single group. Here we aimed at opening the black-box of the phytoflagellates (PFs) o20 lm. Haptophytes, chlorophytes, cryptophytes and pigmented dinoflagellates were identified using fluorescent in situ hybridization or by standard 4 0 ,6-diamidino-2-phenylindole staining. Their fluctuations in abundance, cell size, biomass and bacterivory rates were measured through an annual cycle in an oligotrophic coastal system. On average, we were able to assign to these groups: 37% of the total pico-PFs and 65% of the nano-PFs composition. Chlorophytes were mostly picoplanktonic and they never ingested fluorescently labeled bacteria. About 50% of the PF o20 lm biomass was represented by mixotrophic algae. Pigmented dinoflagellates were the least abundant group with little impact on bacterioplankton. Cryptophytes were quantitatively important during the coldest periods and explained about 4% of total bacterivory. Haptophytes were the most important mixotrophic group: (i) they were mostly represented by cells 3-5 lm in size present year-round; (ii) cell-specific grazing rates were comparable to those of other bacterivorous non-photosynthetic organisms, regardless of the in situ nutrient availability conditions; (iii) these organisms could acquire a significant portion of their carbon by ingesting bacteria; and (iv) haptophytes explained on average 40% of the bacterivory exerted by MFs and were responsible for 9-27% of total bacterivory at this site. Our results, when considered alongside the widespread distribution of haptophytes in the ocean, indicate that they have a key role as bacterivores in marine ecosystems.

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“…Previous studies have indicated a declining gradient in nutrient concentration from the coastal area to offshore (Zhang et al, 2007). The phytoplankton community structure and the interactions between phytoplankton and zooplankton in the ECS have been shown to vary across this nutrient gradient (Chan et al, 2003;Chang et al, 2009;Jiao et al, 2002;Tsai et al, 2011). These studies focused on pico-and nano-phytoplankton rather than microphytoplankton.…”

Section: Sites Descriptionsmentioning

confidence: 99%

Scaling of growth rate and mortality with size and its consequence on size spectra of natural microphytoplankton assemblages in the East China Sea

et al. 2013

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Allometric scaling of body size versus growth rate and mortality has been suggested to be a universal macroecological pattern, as described by the metabolic theory of ecology (MTE). However, whether such scaling generally holds in natural assemblages remains debated. Here, we test the hypothesis that the size-specific growth rate and grazing mortality scale with the body size with an exponent of −1/4 after temperature correction, as MTE predicts. To do so, we couple a dilution experiment with the FlowCAM imaging system to obtain size-specific growth rates and grazing mortality of natural microphytoplankton assemblages in the East China Sea. This novel approach allows us to achieve highly resolved size-specific measurements that would be very difficult to obtain in traditional size-fractionated measurements using filters. Our results do not support the MTE prediction. On average, the size-specific growth rates and grazing mortality scale almost isometrically with body size (with scaling exponent ∼0.1). However, this finding contains high uncertainty, as the size-scaling exponent varies substantially among assemblages. The fact that size-scaling exponent varies among assemblages prompts us to further investigate how the variation of size-specific growth rate and grazing mortality can interact to determine the microphytoplankton size structure, described by normalized biomass size spectrum (NBSS), among assemblages. We test whether the variation of microphytoplankton NBSS slopes is determined by (1) differential grazing mortality of small versus large individuals, (2) differential growth rate of small versus large individuals, or (3) combinations of these scenarios. Our results indicate that the ratio of the grazing mortality of the large size category to that of the small size category best explains the variation of NBSS slopes across environments, suggesting that higher grazing mortality of large microphytoplankton may release the small phytoplankton from grazing, which in turn leads to a steeper NBSS slope. This study contributes to understanding the relative importance of bottom-up versus top-down control in shaping microphytoplankton size structure

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Importance of bacterivory by pigmented and heterotrophic nanoflagellates during the warm season in a subtropical western Pacific coastal ecosystem

Cited by 51 publications

References 63 publications

Seasonal variations of virus- and nanoflagellate-mediated mortality of heterotrophic bacteria in the coastal ecosystem of subtropical western Pacific

Seasonal variations of virus- and nanoflagellate-mediated mortality of heterotrophic bacteria in the coastal ecosystem of subtropical western Pacific

Mixotrophic haptophytes are key bacterial grazers in oligotrophic coastal waters

Scaling of growth rate and mortality with size and its consequence on size spectra of natural microphytoplankton assemblages in the East China Sea

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