Abstract
The Dutch government has a responsibility for the state of the North Sea environment following from the EU’s Marine Strategy Framework Directive and Habitat and Birds Directive. In order to utilize the momentum of the large-scale development of offshore wind farms, a commitment was explicitly included in the site decisions for developers. This enables them to contribute to the strengthening of nature and the preservation and sustainable use of species and habitats that originally existed in the Netherlands (Blauwwind, 2019).
Blauwwind is currently operating the Borssele III and IV wind farm on the southern edge of the Dutch exclusive economic zone. Blauwwind developed its vision on how to design and construct the Borssele III and IV wind farm in such a manner that it matches the vision mentioned above, trying to contribute to a strong, healthy and biodiverse North Sea. (Blauwwind, 2019). In partnership with The Rich North Sea programme, a nature enhancement project is carried out and monitored.
In October 2020, biodiversity was monitored around eight wind turbines in the Borssele wind farm, site III and IV (T-0). Also, living flat oysters were installed at the scour protection of four wind turbines in site III. The scour protection, consisting of different sizes of rock, will also partly be covered with shell material to create settlement places for flat oysters, during the T-1. This site, as well as site IV will be monitored for the development of the surrounding fauna at different scour-protections in 2021, 2023 and 2028. The scope of this monitoring entails measuring growth of the oysters, taking water samples for larvae and eDNA analysis, oyster samples from the baskets (for reproduction and Bonamia status) and a combined video and photo survey of the scour protection with an ROV.
Research questions that could (partly) be answered in the T-1 are:
1) What is the survival and growth rate of flat oysters?
2) Do the flat oysters produce larvae?
3) Do the flat oysters stay free of the parasite Bonamia?
4) How is biodiversity in general developing on the different substrate variations?
5) Are there species-specific responses in relation to current directions or rock size of the scour?
6) Is the species data found by ROV (remotely operated vehicle) video and photo analyses correlated to the eDNA data? Which species are not found or only found by a certain method?
7) How fast does succession of a hard substrate community occur in the Borssele area?
The current report will describe the T-1 monitoring in 2021, its results in terms of description of the situation and a comparison with the T-0 baseline data (Schellekens et al., 2021). Methods are described in more detail in the next chapter, followed by the results and a discussion. This report does not, however, present conclusions on trends or effects of different treatments since this is only presentation of results of the T-1 monitoring, and hence too early to conclude on these results.