SS4.09 Does Intentional Nutrient Fertilization (N,P And Fe) Foster C Sequestration and/or Increased Fish Fertilization?
Date: Tuesday, June 11, 2002
Time: 11:30:00 AM
Location: Colwood
 
VerityPG, Skidaway Institute of Oceanography, Savannah, USA, peter@skio.peachnet.edu
 
THE IMPACT OF GRAZING BY MICROZOOPLANKTON DURING ECOSYSTEM RESPONSE TO IRON ENRICHMENT IN THE SOUTHERN OCEAN IN AUSTRAL SPRING
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During an austral spring Fe fertilization study in the Atlantic/Indian Ocean sector of the Southern Ocean (EisenEx), microzooplankton grazing of <200 um primary production was measured using the dilution method. Initially, fertilized and control (nonfertilized) sites showed statistically similar phytoplankton growth rates and grazing losses to microzooplankton. Much daily production by small phytoplankton was ingested, leaving little for consumption by metazooplankton or for vertical export. In general, this pattern continued at the nonfertilized sites throughout the 4-week study. In contrast, within one week of enrichment, growth rates of nano- and microphytoplankton increased significantly, especially small flagellates and naviculoid diatoms. Grazing by small protozooplankton lagged this response by ca. one week, which resulted in increased phytoplankton abundance. Microzooplankton grazing then ramped up, so that further increases in nano- (especially) and microalgae were reduced. In fact, overgrazing by microzooplankton of the iron-stimulated response of small phytoplankton apparently was prevented only by predation of microzooplankton by larger metazooplankton. Thus, the accumulation of biomass of small phytoplankton in this region during austral spring is best considered to be grazer-limited rather than iron-limited.