Abstract
A previous desk study has shown that a possible future large-scale increase in offshore wind farms in North Sea may have ecosystem effects on the North Sea (Boon et al. 2018; commissioned by RWS and the Ministry of Economic Affairs). This concerns either effects that are not currently occurring, or that are not yet relevant on the scale of the North Sea ecosystem but may become relevant in the future. To gain timely insight in these processes, Wozep has initiated the current research, which builds on the 2018 desk study. Wozep focuses primarily on the effects on offshore wind on species with protected status. An important question is therefore: to what extent do effects of offshore wind farms affect these species through the physical processes, the growth of algae and further through the food chain?
In the present study, this question is approached both top-down and bottom-up. The top-down approach assesses the top predators (birds, marine mammals) and analyses how and to what extent these species can influenced by changes in the food web. The bottom-up approach uses a number of integrated numerical models (modelling suite) to examine how changes in currents and fine sediment dynamics influence the growth of phytoplankton and how this subsequently affects higher layers in the food web. A new modelling suite has been tested in this bottom-up approach. Three scenarios have been calculated with this. A "reference scenario" without the presence of wind farms in the North Sea, a "2020 scenario" containing the wind farms that are already present and a hypothetical upscaling scenario, based on the forecast of the wind industry in 2050. The aim was to get a first impression of the order of magnitude of bottom-up changes, and in which parts of the North Sea these will be larger or smaller.