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Appl Environ Microbiol. 1985 August; 50(2): 187-193
Copyright © 1985, American Society for Microbiology. All Rights Reserved.

Potential Importance of Fish Predation and Zooplankton Grazing on Natural Populations of Freshwater Bacteria {dagger}

Bo Riemann

Freshwater Biological Laboratory, University of Copenhagen, DK-3400 Hillerød, Denmark

ABSTRACT

The rates of ingestion of natural bacterial assemblages by natural populations of zooplankton (>50 µm in size) were measured during a 19-day period in eutrophic Frederiksborg Slotssø, Denmark, as well as in experimental enclosures (containing 5.3 m3 of lake water). The fish and nutrients of the enclosures were manipulated. In enclosures without fish, large increases in ingestion by zooplankton >140 µm in size were found (up to 3 µg of C liter–1 h–1), compared with values less than 0.3 µg of C liter–1 h–1 in the enclosures with fish and in the open lake. Daphnia cucullata and D. galeata dominated the community of zooplankton of >140 µm. Ingestion rates for zooplankton between 50 and 140 µm decreased after a period of about 8 days, in all enclosures and in the lake, to values below 0.1 µg of C liter–1 h–1. On the last 2 sampling days, somewhat higher values were observed in the enclosures with fish present. The >50-µm zooplankton ingested 48 to 51% of the bacterial net secondary production in enclosures without fish, compared to 4% in the enclosures with added fish. Considering the sum of bacterial secondary production plus biomass change, 35 to 41% of the available bacteria were ingested by zooplankton of >50 µm in the enclosures without fish, compared with 4 to 6% in the enclosures with added fish and 21% in the open lake. Fish predation reduced the occurrence of zookplankton sized >50 µm and thus left a large proportion of the available bacteria to zooplankton sized <50 µm. In fact, there were 4.6 x 103 to 5.0 x 103 flagellates (4 to 8 µm in size) ml–1 in the enclosures with fish added as well as in the lake, compared with 0.5 x 102 to 2.3 x 102 ml–1 in the enclosures without fish. This link in the food chain was reduced when fish predation on zooplankton was eliminated and a direct route of dissolved organic matter, via the bacteria to the zooplankton, was established.

FOOTNOTES

{dagger} Contribution no. 425 from the Freshwater Biological Laboratory.

Appl Environ Microbiol. 1985 August; 50(2): 187-193
Copyright © 1985, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Work, K. A., Havens, K. E. (2003). Zooplankton grazing on bacteria and cyanobacteria in a eutrophic lake. J PLANKTON RES 25: 1301-1306 [Abstract] [Full Text]  
  • Havens, K. E., Work, K. A., East, T. L. (2000). Relative efficiencies of carbon transfer from bacteria and algae to zooplankton in a subtropical lake. J PLANKTON RES 22: 1801-1809 [Abstract] [Full Text]  
  • Jurgens, K., Jeppesen, E. (2000). The impact of metazooplankton on the structure of the microbial food web in a shallow, hypertrophic lake. J PLANKTON RES 22: 1047-1070 [Abstract] [Full Text]  


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