The standard concept for the investigation of the impacts of offshore wind turbines on the marine environment (StUK) of the German Federal Maritime and Hydrographic Agency (BSH) prescribes extensive investigations on the benthic communities of the seafloor as well as on the fouling assemblages on the underwater structures of offshore wind turbines. The construction of the test site alpha ventus allowed for the first time for testing the appropriate-ness of these investigations. In the present sub-project of the StUKplus research project, the investigations according to StUK3 (BSH, 2007) were spatially and temporally extended in order to test for effects on the benthic system which could otherwise not be revealed by the StUK procedures. In the first work package of the sub-project an additional complete sam-pling campaign according to StUK was performed in the second year of the operational phase of the wind farm. The results of this work package indicate differential temporal variations of the benthic communities and of sedimentological parameters inside the wind farm and in a reference area outside the wind farm. However, the differences were mainly temporary fluctuations while persistent effects of the construction and operation of the wind farm on the benthos were not evident. Solely the biomass and species richness of the fouling assemblage on the underwater structures increased continuously since the construction of the turbines. In the second work package the turbine-related effect monitoring of the benthic communities of the seafloor was extended to the entire distance between two neighbouring turbines. No ef-fects of the turbines on the benthos and the sediment could be detected in this work package. The spatial resolution of the turbine-related effect monitoring was inadequate for detecting processes which occur in the vicinity of the turbine foundations. In none of the two work packages did the spatial and temporal extension of the benthos monitoring provide additional findings. However, deficiencies of the benthos ecological investigations according to StUK3 became evident and improvements could be deduced.