Role of light for consumer-dynamics and nutrient turnover in microbial food webs of the marine pelagial
Final Report Abstract
In this project the exponentially fed batch (EFB), as a reliable alternative to chemostat systems, was successfully evaluated and applied in all experiments, conducted to get a mechanistic understanding regarding the ecological significance and niches of mixotrophic flagellates. The results show, that ability of a mixotroph to compete with a heterotroph for common prey (picoplankton) depends on the combination of light intensity and loss rate/turnover rate. The mixotroph (MF) was dominant under conditions of high light – low loss rate, while the heterotroph (HF) was dominant under conditions of low light – high loss rate. Under conditions favorable for the HF more nutrients may be re-mineralized, enhancing picoplankton growth. Consequently, abundances of prey were negatively related to light, this is light indirectly controlled the specific loss/growth rates (and standing stock) of the picoplankton. Further, the results indicate that the identity of the limiting nutrient has no effect on the competition between MF and HF under conditions which are anyways favorable for the MF. However, the transition point from “MF dominated” to “HF dominated” and vice versa, seem to shift based on the identity of the limiting nutrient. The results of this project provide first empirical evidence for a framework that allows a better understanding the prevalence of mixotrophic algae especially in oligotrophic areas. The results also show that the conventional concept of the microbial loop needs to be updated, as the classical theorem sees heterotrophic bacterivores as the major grazers of bacteria; our results allow a more differentiated picture.
Publications
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Relative importance of mixotrophy along gradients of light and loss-rates. (05.-09. September 2011, Oldenburg 41st Annual Meeting of the Ecological Society of Germany, Austria and Switzerland (GFÖ)
Fischer, R, H. Hillebrand and R. Ptacnik
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Relative importance of mixotrophy along gradients of light and loss-rates. (16.-19. October 2012, Heraklion, Crete, Greece, MESOAQUA International Symposium - Recent achievements and future direction in Aquatic Mesocosm Research)
Fischer, R, H. Hillebrand and R. Ptacnik
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Relative importance of mixotrophy along gradients of light and loss-rates. (18.-23. August 2013, London, England, 11th INTECOL Congress, Ecology: Into the next 100 years)
Fischer, R, H. Hillebrand and R. Ptacnik
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The exponentially fed batch culture as a reliable alternative to conventional chemostats. Limnology & Oceanography Methods, 12, 2014, 432–440
Fischer, R., T. Andersen, H. Hillebrand and R. Ptacnik
