Samenvatting

The restoration of native flat oyster (Ostrea edulis) reefs in Lake Veere is a key ecological goal of the Oyster Heaven project. However, successful reef development may be hindered by predation. The European green crab *(Carcinus maenas),* a known bivalve predator in Lake Veere. This study investigated how crab predation on juvenile oysters is influenced by three factors: the structural arrangement of the blocks (treatments), the size of the oyster spat, and the height at which the oysters are located on the blocks. A series of three controlled experimental runs was conducted using reef blocks with attached oysters and individual crabs in tanks under standardized conditions. Results showed the highest predation rate within the control (without reef structure) and significantly lower in treatments where blocks were placed in the upright position. A significant negative relationship between oyster size and predation was found in one of the three runs, suggesting larger oysters are less vulnerable. Even though this trend was not consistent throughout all runs. Additionally, oysters settled lower on the blocks experienced significantly more predation than those positioned higher, likely due to greater accessibility for crabs. To assess whether oyster size corresponded with nutritional value, a condition index (CI) was calculated based on dry tissue and shell weights (Rainier & Mann, 1992). Larger oysters exhibited a slightly higher CI, suggesting a potentially greater energy value to crabs, although variation in CI between size classes was small and differences were not ecologically significant. While the sample size was sufficient, variability between runs highlights the importance of replication and further research. Future studies should focus on increasing the number of replicates and incorporating more structurally complex and ecologically realistic reef setups to better understand predation dynamics on restored ‘mother reefs.’