MEPS 521:19-30 (2015)  -  DOI: https://doi.org/10.3354/meps11124

ABSTRACT: Using a previous model based on the microbial hub (HUB; consists of heterotrophic bacteria and microzooplankton, the latter being heterotrophic protists), we investigated the effects of competition for inorganic and organic resources in planktonic food webs by proposing and developing the concept of ‘competition switches’. A competition switch controls the flow of carbon toward either the HUB or other food web compartments. The 3 switches are PB: competition for inorganic nutrients between bacteria and phytoplankton; MB: competition for detritus between bacteria and mesozooplankton; and Mµ: competition for large-sized phytoplankton production between microzooplankton and mesozooplankton. Here, we explored the novel hypothesis that competition for resources between the HUB and other food web compartments plays a crucial role in controlling the flows of biogenic carbon in the euphotic zone. We ran a numerical model to determine the potential effects of the 3 competition switches and found that the most important switch is MB, followed by PB and Mµ. Comparison of our model results with field data indicated that the strong effects of HUB competition for resources with phytoplankton and mesozooplankton exist both in our model as well as in the world ocean. Finally, comparison of our model results with carbon flows estimated by the linear inverse approach showed that the competition switches can determine large changes in the flows of carbon in marine pelagic food webs. The focus of our study was the propagation of competition effects that occur at the core of the food web.

KEY WORDS: Planktonic food webs · Competition switches · Carbon flow · Microbial hub · Phytoplankton · Bacteria · Microzooplankton · Mesozooplankton