ostreae, which affects the health of the oyster and increases mortality at a later age (Engelsma et al., 2010). The pressure on the survival of the oysters is further confounded by the presence of the parasite B. edulis by providing substrate and refuge from predation (Christianen et al., 2018). gigas may facilitate settlement of larvae and survival of juvenile O. However, there is evidence suggesting that adult C. Larvae of both oyster species are often found at similar times in the water column, and as spat, the two oyster species compete for space on appropriate substrate (Smaal & Lucas, 2003). Since its introduction in the Netherlands, the Pacific oyster ( Crassostrea gigas) has become widely established in the same waterbodies that O. Settled spat is also under pressure from predation, and from competition for space with conspecifics or other settling organisms (Engelsma et al., 2010). There is generally a considerable loss of individuals between the larval and spat phases, potentially due to unsuccessful metamorphosis, predation of larvae in the water column, and the lack of appropriate substrate on which to settle (Filgueira, Brown, Comeau, & Grant, 2014 Korringa, 1940). edulis larvae are released into the water column and after a pelagic stage of about 10 days the larvae search for suitable hard substrate on which to settle and develop into oyster spat, this last stage is called spatfall. the eggs are fertilized within the mantle cavity where they develop into larvae over 6–10 days (Korringa, 1940). In addition, flat oysters are a brooding species, i.e. The spawning success of adults can vary between locations and seasons (Korringa, 1940). The oyster experiences environmental pressures and consequent population bottlenecks at every life stage. edulis in the North Sea is not a simple task. edulis in the North Sea and Dutch delta are motivated by: 1) restoring the local ecosystem and increasing the biodiversity in and around the reefs 2) utilizing the possible ability of the reefs to reduce erosion around the base of planned wind turbines and 3) the economic possibility of restoring the flat oyster market to its former glory. edulis restoration projects have been set up in the North Sea, off the coast of the Netherlands (e.g. This may therefore be the ideal time to attempt to restore flat oyster reefs. However, the flat oyster population in the Dutch Delta area is showing signs of recovery, particularly in Lake Grevelingen (Smaal, Kamermans, Van der Have, Engelsma, & Sas, 2015). edulis has declined considerably due to increased mortality as a result of overfishing around the end of the 19 th and beginning of the 20 th centuries (Gercken & Schmidt, 2014) and more recently due to the parasite Bonamia ostreae (Engelsma et al., 2010). The flat oyster not only acted as a keystone species for a rich and productive ecosystem, but also served as an economically profitable fisheries product (Gercken & Schmidt, 2014). The European flat oyster ( Ostrea edulis), was once widespread in the southern North Sea (Olsen, 1883). edulis spat collectors intended for reef restoration purposes but may need further development for cultivation application. Suspended sacks of bivalve shells show great promise as O. Fouling was heavy and may have prevented larval settlement on collectors deployed too early.In general, most spat were observed on collectors deployed 1–2 weeks after the peak in larval abundance was detected.The most successful spat collectors were sacks of bivalve shells.edulis and the non-indigenous Pacific oyster ( Crassostrea gigas) varied between locations and years. Larval abundance, and timing of peaks in abundance for both O.These different types included Chinese hats, Vexar mesh, PVC tubes, and four types of bivalve shells. The results of four different experiments investigating larval abundance, and the use of seven different types of suspended spat collectors in seven locations in the SW Netherlands were compared.Efficient spat collection is essential to both the successful restoration and cultivation of the European flat oyster ( Ostrea edulis).

Oyster spat growin