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|The Return of the Rightful Oyster : A meta-analysis, including burial experiment, on the restoration of the European flat oyster (Ostrea edulis)|
van Houten, N. (2019). The Return of the Rightful Oyster : A meta-analysis, including burial experiment, on the restoration of the European flat oyster (Ostrea edulis)
. BSc Thesis. NIOZ Royal Netherlands Institute for Sea Research: Yerseke. 49 pp.
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AbstractOysters provide valuable ecosystem services, in which many humans and ecosystems benefit from. By building biogenic reefs, they provide physical coastal defence, as well as promote biodiversity through providing shelter and habitat. Also, oysters filter the water column. Water filtering decreases turbidity and induces a cascade of positive feedback loops (e.g. improving water quality and consequently primary production due to better light penetration). However, the Netherlands has not recorded any self-sustaining European flat oyster (Ostrea edulis) populations since 1962. Centuries of overexploitation and disease has caused this species to become functionally extinct. Without O. edulis, a gap in trade and ecological service was created. In an attempt to temporarily fill this gap, the Japanese oyster (Crassostrea gigas) was introduced in the 1960s. Originally, it was believed that C. gigas would not be able to survive in the North Sea. However, almost four decades later, C. gigas is still present and has expanded at the expense of the native European flat oyster. To recover O. edulis populations, restoration efforts are necessary. Earlier restoration efforts worldwide have proven to be difficult. Therefore, to improve restoration success rates, I used a meta-analytic approach. I evaluated scientific literature about oyster history in the Netherlands, as well as in other countries. Further, environmental conditions and biological processes affecting oyster’s ecological and economic value, as well as previous global restoration attempts and policy making was reviewed. Also, I have conducted an experiment on the effects of burial and positioning on filtration rate. I have linked filtration rate with reef resilience and discussed how this can influence restoration designs. The results suggest that oysters at low burial depths in the vertical treatment are less stressed then horizontal treatments. High burial depths stressed the oysters regardless of treatment positioning. These results suggest that O. edulis positioning can impact filtration and possibly burial resilience in oyster reefs. Considering my results, in congruence with the scientific literature reviewed, future restoration designs can be improved by reviewing more site- and species-specific research and apply pre- and post-restoration assessments.