Bacterial growth rate and the relative abundance of bacteria to heterotrophic nanoflagellates in the euphotic and disphotic layers in temperate coastal waters of Sagami Bay, Japan

Youta Sugai, Kenji Tsuchiya, Victor S. Kuwahara, Shinji Shimode, Kazuhiro Komatsu, Akio Imai, Tatsuki Toda

Abstract

This study aimed to clarify the vertical differences in bacterial growth and grazing pressure on bacteria by heterotrophic nanoflagellates (HNF) and to identify the controlling factors of bacterial growth in temperate coastal waters of Sagami Bay, Japan. In addition to environmental factors, the annual monthly variations in bacterial growth rate (BGR) and the relative abundance of bacteria to HNF (BA/HNFA) were investigated in the euphotic and disphotic layers between May 2012 and May 2013. Significant vertical differences in BGR and BA/HNFA were evident between the two layers during the thermal stratification times of May to October 2012 and April to May 2013. BGR indicated significantly stronger limitation of bacterial growth in the euphotic layer compared to the disphotic layer. In contrast, significantly lower BA/HNFA was observed in the euphotic layer, suggesting significantly higher grazing pressure on bacteria by HNF. However, significant differences in BGR and BA/HNFA were not observed between the two layers from November 2012 to Match 2013, when the water column was well-mixed vertically due to the cooling and wind-induced mixing of surface water. This study indicates that bacteria in the euphotic layer grow less actively and are more vulnerable to predatory grazing by HNF relative to the disphotic layer during the stratification period. Further, multiple regression analyses indicate that bacterial growth was most controlled by the concentrations of chlorophyll a and dissolved organic carbon in the euphotic and disphotic layers, respectively.

Original languageEnglish
Pages (from-to)1-11
Number of pages11
JournalJournal of Oceanography
DOIs
StateAccepted/In press - 2016 Feb 5

Fingerprint

bacterium
grazing pressure
coastal water
relative abundance
stratification
dissolved organic carbon
annual variation
multiple regression
chlorophyll a
environmental factor
grazing
water column
cooling
surface water

Keywords

  • Disphotic layer
  • Euphotic layer
  • Grazing pressure
  • Growth rate
  • Heterotrophic bacteria
  • Heterotrophic nanoflagellate
  • Microbial loop
  • Temperate coastal water

ASJC Scopus subject areas

  • Oceanography

Cite this

Bacterial growth rate and the relative abundance of bacteria to heterotrophic nanoflagellates in the euphotic and disphotic layers in temperate coastal waters of Sagami Bay, Japan. / Sugai, Youta; Tsuchiya, Kenji; Kuwahara, Victor S.; Shimode, Shinji; Komatsu, Kazuhiro; Imai, Akio; Toda, Tatsuki.

In: Journal of Oceanography, 05.02.2016, p. 1-11.

Research output: Contribution to journalArticle

Sugai, Youta; Tsuchiya, Kenji; Kuwahara, Victor S.; Shimode, Shinji; Komatsu, Kazuhiro; Imai, Akio; Toda, Tatsuki / Bacterial growth rate and the relative abundance of bacteria to heterotrophic nanoflagellates in the euphotic and disphotic layers in temperate coastal waters of Sagami Bay, Japan.

In: Journal of Oceanography, 05.02.2016, p. 1-11.

Research output: Contribution to journalArticle

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keywords = "Disphotic layer, Euphotic layer, Grazing pressure, Growth rate, Heterotrophic bacteria, Heterotrophic nanoflagellate, Microbial loop, Temperate coastal water",
author = "Youta Sugai and Kenji Tsuchiya and Kuwahara, {Victor S.} and Shinji Shimode and Kazuhiro Komatsu and Akio Imai and Tatsuki Toda",
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AU - Kuwahara,Victor S.

AU - Shimode,Shinji

AU - Komatsu,Kazuhiro

AU - Imai,Akio

AU - Toda,Tatsuki

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N2 - This study aimed to clarify the vertical differences in bacterial growth and grazing pressure on bacteria by heterotrophic nanoflagellates (HNF) and to identify the controlling factors of bacterial growth in temperate coastal waters of Sagami Bay, Japan. In addition to environmental factors, the annual monthly variations in bacterial growth rate (BGR) and the relative abundance of bacteria to HNF (BA/HNFA) were investigated in the euphotic and disphotic layers between May 2012 and May 2013. Significant vertical differences in BGR and BA/HNFA were evident between the two layers during the thermal stratification times of May to October 2012 and April to May 2013. BGR indicated significantly stronger limitation of bacterial growth in the euphotic layer compared to the disphotic layer. In contrast, significantly lower BA/HNFA was observed in the euphotic layer, suggesting significantly higher grazing pressure on bacteria by HNF. However, significant differences in BGR and BA/HNFA were not observed between the two layers from November 2012 to Match 2013, when the water column was well-mixed vertically due to the cooling and wind-induced mixing of surface water. This study indicates that bacteria in the euphotic layer grow less actively and are more vulnerable to predatory grazing by HNF relative to the disphotic layer during the stratification period. Further, multiple regression analyses indicate that bacterial growth was most controlled by the concentrations of chlorophyll a and dissolved organic carbon in the euphotic and disphotic layers, respectively.

AB - This study aimed to clarify the vertical differences in bacterial growth and grazing pressure on bacteria by heterotrophic nanoflagellates (HNF) and to identify the controlling factors of bacterial growth in temperate coastal waters of Sagami Bay, Japan. In addition to environmental factors, the annual monthly variations in bacterial growth rate (BGR) and the relative abundance of bacteria to HNF (BA/HNFA) were investigated in the euphotic and disphotic layers between May 2012 and May 2013. Significant vertical differences in BGR and BA/HNFA were evident between the two layers during the thermal stratification times of May to October 2012 and April to May 2013. BGR indicated significantly stronger limitation of bacterial growth in the euphotic layer compared to the disphotic layer. In contrast, significantly lower BA/HNFA was observed in the euphotic layer, suggesting significantly higher grazing pressure on bacteria by HNF. However, significant differences in BGR and BA/HNFA were not observed between the two layers from November 2012 to Match 2013, when the water column was well-mixed vertically due to the cooling and wind-induced mixing of surface water. This study indicates that bacteria in the euphotic layer grow less actively and are more vulnerable to predatory grazing by HNF relative to the disphotic layer during the stratification period. Further, multiple regression analyses indicate that bacterial growth was most controlled by the concentrations of chlorophyll a and dissolved organic carbon in the euphotic and disphotic layers, respectively.

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