Abstract
As part of the Gemini oyster bed restoration project WINOR (De Rijke Noordzee, WaterProof, NIOZ, Waardenburg Ecology, Wageningen Marine Research, and Gemini), an initial population of flat oysters (Ostrea edulis) was introduced into the Gemini ZeeEnergie offshore wind farm in 2021 and 2022. To determine whether these flat oysters reproduced on site and whether the larvae could settle as spat, an experiment was conducted in 2023 to capture oyster larvae on spat collectors attached to metal frames. The spat collectors consisted of four 30-liter bags per metal frame, two of which were filled with dead Japanese oyster shells and two with dead Japanese oyster shells treated with BESE reef paste (ground oyster shells bound with an environmentally friendly binder). Due to logistical problems, the frames were deployed several weeks later than planned. The deployment of the frames themselves was successful, but locating and retrieving them proved to be very complicated. The research into this is described in the report by Kamermans et al. (2024). Ultimately, half of the spat collectors were recovered (October 2024), a year later than planned and after the publication of the report by Kamermans et al. (2024).
The shell material from the recovered bags was inspected for the presence of flat oyster spat and other larger, conspicuous species. A total of 12 oyster spat were found. DNA analysis determined that these were all Pacific oysters (Magallana gigas). Notable species found in the bags included North Sea crab (Cancer pagurus), slipper limpet (Crepidula fornicata), scaly clam (Heteranomia squamula), velvet swimming crab (Necora puber), butterfish (Pholis gunnellus), Norwegian barnacle (Ciliata septentrionalis), hairy crab (Pilumnus hirtellus), porcelain crab (Pisidia longicornis), and spiny sandworm (Sabellaria spinulosa). At first glance, treatment with BESE does not appear to have increased the settlement density, but too few broods have been found to draw any conclusions.