Micro-grazer biomass, composition and distribution across prey resource and dissolved oxygen gradients in the far eastern tropical north Pacific Ocean

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• 作者：M. Brady Olson ; ¹ ; ^{brady.olson@www.edu} ; Kendra L. Daly
• 关键词：Micro-grazers ; Ciliates ; Dinoflagellates ; Oxygen minimum zone ; Grazing
• 刊名：Deep Sea Research Part I: Oceanographic Research Papers
• 出版年：2013
• 出版时间：May, 2013
• 年：2013
• 卷：75
• 期：Complete
• 页码：28-38
• 全文大小：1250 K

文摘

The ecology of micro-grazers (m>Mm>_m>gm>) was investigated across prey and dissolved oxygen (DO) gradients in the eastern tropical north Pacific Ocean (ETNP) during October-November 2007. Surface (<200 m) chlorophyll m>am> (Chl m>am>) across m>am> ¡«1700 km north-south transect ranged between the seasonal average of 0.2 ¦Ìg Chl m>a m>L^?1 to 1.8 ¦Ìg Chl m>a m>L^?1 in an extensive Chl m>am>-rich patch in the center of the transect. Limiting (<20 ¦Ìmol kg^?1 O₂) DO concentrations were encountered as shallow as 24 m. Biomass of m>Mm>_m>gm> in waters above the upper oxycline (UO) ranged between 5.6 ¦Ìg C L^?1 and 36.6 ¦Ìg C L^?1, with highest m>Mm>_m>gm> biomass observed in locations with highest Chl m>am>. Heterotrophic dinoflagellates contributed most, on average, to m>Mm>_m>gm> biomass (41 % to 53 % ), followed by aloricate spirotrich ciliates (24 % to 29 % ) and heterotrophic nanoflagellates (11 % to 33 % ). Biomass of m>Mm>_m>gm> decreased, on average, over 96 % in waters below the UO, but this decrease did not appear to be regulated by DO; m>Mm>_m>gm> biomass more strongly correlated with Chl m>am> (m>rm>=0.83, m>Pm><0.001) and temperature (m>rm>=0.76, m>Pm><0.001) at discrete depths than with DO (m>rm>=0.67, m>Pm><0.001). Using a multiple stepwise regression model, Chl m>am> alone accounted for 68 % m>Mm>_m>gm> biomass variability, whereas Chl m>am> and temperature combined accounted for 84 % . In two m>Mm>_m>gm> grazing experiments we found that m>Mm>_m>gm> removed 33 % and 108 % of surface primary production in the upper mixed layer. These estimates of m>Mm>_m>gm> grazing, while limited in scope, fall within estimates from other regions of the equatorial Pacific Ocean, and help reinforce the paradigm that m>Mm>_m>gm> are influential in regulating organic carbon dynamics in the eastern tropical Pacific. A primary finding from this study was that observations of m>Mm>_m>gm> biomass are higher than previously reported for the ETNP. This observation suggests that the region¡¯s complex air-sea interactions and the resultant positive influence on primary production and phytoplankton biomass can episodically support high biomass of a diverse m>Mm>_m>gm> community.