MEPS 339:41-47 (2007)  -  doi:10.3354/meps339041

ABSTRACT: While we have some understanding about the influence of physical processes on biological variables, our knowledge about biological-physical feedback loops in marine ecosystems is scarce. In this model study the impact of cyanobacteria on their environment and life cycle stages is assessed by a coupled biological-physical model. Several positive and negative feedback loops are identified including a short temperature-cyanobacteria-temperature loop which is embedded into longer ones running on the seasonal time scale. The short positive feedback loop leads to an increase of cyanobacteria and a simultaneous decrease of eukaryotic phytoplankton biomass in summer. However, the induced changes in the nutrient and temperature field result in enhanced eukaryotic phytoplankton growth in autumn, which degrades winter light conditions for resting spores of cyanobacteria. Nevertheless, positive feedback prevails and overall, cyanobacteria gain from their own presence. This study emphasizes the importance of considering species and life cycle characteristics in studies dealing with feedback mechanisms.

KEY WORDS: Cyanobacteria · Phytoplankton · Feedback mechanisms · Life cycle · Heating · Model · Physical-biological interactions