Bonamia-vrije oesters (BO-43-116.01-003, BO-43-021.02-020)

Presently, there is a shortage of flat oysters for future large-scale restoration. Flat oysters are available as adults or as spat. These are either fished from natural beds or culture plots, or produced with collectors in the field, in spatting ponds, or in hatcheries. The quality requirements for flat oysters to be used in restoration pilots are:

• disease free
• tolerance or resistance against diseases when possible
• absence of non-native species
• good survival, growth and reproduction
• adapted to the local environment
• highest possible genetic diversity
• cost efficient.

In 2018-2021 Wageningen Marine Research (WMR), Wageningen Bioveterinary Research (WBVR), the hatchery of Roem van Yerseke (RvY) en the Spanish University of Santiago (USC) showed that it is possible to select Bonamia-free broodstock from a Bonamia-infected population. Bonamia-free offspring was produced which contained markers genes suggesting better resilience to the disease. This offers opportunities for restoration projects: Bonamia-free flat oysters can be produced that are more resilient to the disease, but do not spread the disease. Contamination in the hatchery needs to be minimised. A method for water treatment was developed in 2021 and needs to be tested in 2022. A disadvantage of hatchery production is inbreeding. Use of different broodstocks can reduce this risk. A genetic analysis can provide guidelines. Oysters produced in a hatchery are not necessarily most adapted to North Sea conditions. Adaptive capacity can be tested experimentally by exposing different populations to North Sea conditions.

The project aims to fill in knowledge gaps concerning (1) water treatment to keep hatcheries disease free, (2) secure the desired genetic diversity of oysters for restoration projects, (3) test adaptation capacity of oysters under North Sea conditions.