The combined effects of global warming and anthropogenic pressures such as fishery and (de)eutrophication on marine and coastal ecosystems are difficult to assess and can be counterintuitive. For example, in the coastal Southern North Sea (SNS), observed chlorophyll concentrations increased in spite of a significant reduction in nutrient loads. Most models so far failed to reproduce this trend because they assume a bottom-up control of ecosystem dynamics. Here, we use a coupled model system (MOSSCO-GETM-MAECS) with a realistic representation of turbidity in near-coast waters. High turbidity not only impedes autotrophic growth due to light limitation but also creates a refuge for juvenile fish so that carnivorous grazing on zooplankton increases towards the coast. We validate long-term simulations of the SNS against satellite and in-situ observations, and show that climate warming has intensified temperature-dependent carnivory, which through reduced herbivory positively affects net phytoplankton growth. The simulated long-term change in coastal carnivory matches well an observed increase in juvenile fish biomass. Our study highlights the relevance of turbidity and resulting top-down control for the sensitivity of marine ecosystems to global change. 

Primary Presenter: Shubham Krishna, Helmholtz Center Hereon (Shubham.Krishna@hereon.de)

Authors:

Carsten Lemmen,   ()

Nik Probst,   ()

Ovidio Garcia,   ()

Kai Wirtz,   ()