Target monitoring in offshore windfarms—the need to understand cause–effect relationships in the marine benthos

In many European countries offshore windfarm projects are accompanied by obligatory environmental impact assessments, including baseline monitoring of the marine benthos and demersal fish. The effects of offshore windfarm developments on the benthic system are complex.
However, legal baseline monitoring merely allows for net effect descriptions but not for identifying and understanding the underlying processes. Instead, key processes should be identified and become subject to hypotheses-based target monitoring and/or experimental studies in order to make environmental impact assessments more efficient and reduce duplication internationally. We compiled an overview over the anthropogenic activities associated with the construction and
operation of offshore windfarms and identified cause–effect relationship to facilitate the development of specific hypotheses. We expect offshore windfarming activities to modify the geomorphological and hydrodynamic environment at different temporal and spatial scales. The environmental effects will have consequences for the behaviour and physiology of benthic organisms, including demersal fish, restructuring natural local populations and communities.
Major effects on biological production, biogeochemical processes, as well as on structure and function related to biodiversity, are expected from the massive colonization of the artificial underwater constructions by a specific hard-bottom fauna which is naturally missing in soft sedimentary habitats. Understanding the mechanisms behind these changes is a priority for assessing and predicting the ecological implications for the benthic system. Such predictions may help to develop science-based mitigation actions.