listingsasfen.blogg.se

If artificial habitats hold similar communities, they could be considered as desirable as well.

These natural reefs, including their epibenthic community, qualify for protection under the European Habitat Directive ( European Commission, 1992). Offshore reefs of natural origin in the Netherlands are primarily composed of rocky substrate ( Coolen et al., 2016). To evaluate the ecological potential of such alternatives, more insight is needed into the current state of the epifouling communities present on the structures. Similar proposals (named renewables-to-reefs RTR) may be expected once offshore wind farms reach their end-of-life ( Fowler et al., 2015 Smyth et al., 2015). These include so called rigs-to-reefs (RTR) schemes, in which foundations are to be left at sea as artificial reefs, either left-in-place, toppled over, or relocated ( Picken and McIntyre, 1989 Macreadie et al., 2012). To prevent high removal costs, loss of fishing habitat and to maintain the artificial reef effect of structures, alternative uses for the foundations of these platforms are proposed ( Day and Gusmitta, 2016). Many oil and gas platforms are reaching their financial or technical end-of-life and will be decommissioned ( Royal Academy of Engineering, 2013). At the same time, a large-scale removal of offshore oil and gas installations is expected over the coming years ( Ahiaga-dagbui et al., 2017). In recent years the number of offshore wind farms in the North Sea increased strongly. Furthermore, species richness may increase with installation age ( van der Stap et al., 2016).

For example, epifouling communities on offshore installations evolve over time with dominance changing among species ( Whomersley and Picken, 2003). However, other variables often differ between locations. It is therefore expected that offshore wind farms and oil and gas platforms house similar benthic communities when other environmental variables are constant. Most oil and gas platforms in the North Sea were constructed using steel jacket foundations, which structurally resemble offshore wind-turbine foundations, offering similar substrate to epifouling organisms. Compared with oil and gas, offshore wind is still a young industry. The oldest North Sea offshore wind farm was constructed in 2002 ( Leonhard and Christensen, 2006). Oil and gas companies have been installing platforms in the North Sea since the 1960s ( Shepherd, 2015) and expanded into the Dutch continental shelf (DCS) from the early 1970s onward ( EBN, 2014). Assuming 5 MW turbines, this is the equivalent of 12 400 turbine foundations, all providing artificial hard substrates to epifouling organisms. The European Wind Energy Association estimates that the North Sea will hold up to 62 GW of offshore wind energy installations in 2030 ( EWEA, 2015). As a result of the increasing number of offshore energy devices in the North Sea, the amount of artificial hard substrate increases steadily ( Krone et al., 2013). The introduction of artificial hard substrates in areas dominated by sandy seabeds increases habitat available to epifouling organisms ( Zintzen and Massin, 2010 Lengkeek et al., 2013 De Mesel et al., 2015).