Native oyster enhancement pilot in offshore wind farm Borssele III/IV; a case study for sharing knowledge through The Rich North Sea’s ToolboxBiogenic Reefs

Renate Olie¹, Eline van Onselen¹

¹The North Sea Foundation - The Rich North Sea programme, The Netherlands

For the past five years, The Rich North Sea programme has been working on nature enhancement projects in Offshore Wind Farms (OWFs) in the North Sea. By working together with the offshore industry, scientific institutions, consultancies and governments, knowledge and experience, as well as a vast network of partners and stakeholders was gained. To share all this, The Toolbox was created; an online knowledge hub, filled with information on nature enhancement in OWFs, examples of projects, products, monitoring and practical information. The Toolbox has grown beyond the programme; everyone can add their own project on nature enhancement to the knowledge base. This way, results and practical lessons learned can be shared in a user friendly way to inspire others. The Toolbox will be shown while presenting one of the nature enhancement pilots for the native oyster: a project together with Blauwwind, which is operating offshore wind farm Borssele III/IV. This project used “oyster tables” with baskets as outplacement structures to place 2400 adult native oysters on the scour protection of wind turbines. Monitoring focused on biodiversity as well as oyster reproduction success. Methods were 4K ROV footage, eDNA analysis, larvae sampling and several physical measurements on the oysters and table. The adult oysters showed a high survival rate (on average 70% after 3 years), growth, gonad development and no Bonamia parasites. Young oysters, spat, were found in the baskets as well as on the scour protection. The species community living on the scour protection became more complex between 2020 and 2023 and was more diverse on the armour (coarse) layer than on the filter (fine) layer.