Do bacteria-sized marine eukaryotes consume significant bacterial production?

Area of Science:

• Marine microbial ecology
• Oceanography
• Biogeochemical cycles

Background:

• Bacterioplankton play a significant role in marine primary production, fixing a substantial portion of global carbon dioxide.
• The fate of bacterioplankton, particularly through grazing by bacteriovores, is a key process in marine food webs.
• Current understanding of bacteriovore activity is limited by scarce data and the potential for uncharacterized organisms.

Purpose of the Study:

• To investigate the predominant fate of marine bacterioplankton, focusing on the role of grazing.
• To identify potential grazers responsible for a significant fraction of bacterial consumption in coastal ecosystems.
• To explore the contribution of previously uncharacterized microorganisms to marine carbon cycling.

Main Methods:

• Analysis of marine primary production data, including carbon dioxide fixation attributed to bacterioplankton.
• Assessment of grazing rates in coastal waters using filtration techniques to characterize microbial populations.
• Investigation of the size-fraction of grazers capable of passing 0.6-micrometer filters.

Main Results:

• Bacterioplankton account for up to 60% of marine primary production and about one-fourth of global CO2 fixation.
• Evidence suggests small, uncharacterized eukaryotes passing 0.6-micrometer filters are responsible for over 50% of total grazing in coastal waters.
• These dominant grazers have not been previously observed microscopically.

Conclusions:

• Previously unknown microscopic eukaryotes represent a major, uncharacterized component of marine grazing.
• These findings highlight a significant gap in our understanding of marine microbial food webs and carbon flow.
• Further research is needed to identify and characterize these elusive organisms and their ecological roles.