Inferring time-variable effects of nutrient enrichment on marine ecosystems using inverse modelling and ecological network analysis

- We use LIM and ENA to assess the effects of nutrient addition on marine ecosystems.
- Increasing nutrient supply enhanced net primary production and system activity.
- Food web efficiency and FCI decreased with increasing nutrient addition rates.
- Detritus was dominant food source, regardless of the nutrient addition rates.

We combined data from an outdoor mesocosm experiment with carbon budget modelling and an ecological network analysis to assess the effects of continuous nutrient additions on the structural and functional dynamics of a marine planktonic ecosystem. The food web receiving no nutrient additions was fuelled by detritus, as zooplankton consumed 7.2 times more detritus than they consumed algae. Nutrient supply instantly promoted herbivory so that it was comparable to detritivory at the highest nutrient addition rate. Nutrient-induced food web restructuring reduced carbon cycling and decreased the average number of compartments a unit flow of carbon crosses before dissipation. Also, the efficiency of copepod production, the link to higher trophic levels harvestable by man, was lowered up to 35 times by nutrient addition, but showed signs of recovery after 9 to 11 days. The dependency of the food web on exogenous input was not changed by the nutrient additions.