Abstract
In The Netherlands, the first offshore wind farm (OWF) became fully operational in 2007. This OWF was followed by several others. The establishment of wind farms is accompanied by a rapid colonisation by fouling species, which attach on the newly introduced hard substrates. Monitoring programmes of the communities on wind turbine foundations in the Netherlands have not yet been conducted on a long-term basis (>5 years) after construction. The ‘Monitoring and Research, Nature Enhancement and Species Protection’ (MONS) aims, among many other things, to monitor hard substrate communities in OWFs during the next 10 years. The focus is on differences in succession in OWFs with different characteristics in the various habitats and monitoring long term succession of benthic communities on the turbine foundations and scour protection layer (SPL). Since the execution of hard substrate sampling campaigns in OWFs is challenging and costly, an advice was requested on how to come to a feasible monitoring programme in MONS. For this purpose, the available and to-be-developed sampling methods and legal & safety requirements were evaluated. Multiple methods are available that are or may become suitable but no single method meets all criteria. On the very short term, the only fully suitable method to obtain samples from the turbine foundations, is collection by divers using manual scraping tools and sample nets as has been performed in past research in OWFs and on other offshore installations. However, OWF operators prefer to replace diving work with remotely operated vehicles (ROVs) wherever possible, as part of their legal obligations to minimise health and safety risks. In the next 2 years, an ROV mounted sampling tool in development by Bluestream and Wageningen Marine Research may become a suitable replacement for diver sampling. To collect small rocks from the scour protection layer, multiple methods exist, but for some of the options may not be accepted by OWF operators. The single method likely to be accepted is to make use of ROV mounted manipulator arms, collecting the rocks and depositing them in baskets. This has been applied in the past and the use of ROV tools increases health & safety, which is why this method is likely to be preferred by offshore windfarm operators.