Introduction
European flat oyster reefs (Ostrea edulis) were once abundant in European seas, but have largely disappeared due to overexploitation, decreased water quality, sedimentation, and diseases. The remaining populations are in a degraded state, hampering the provision of ecosystem functions and services (Thomas et al., 2022); habitat provision is marginal as due to low densities of oysters, the typical 3D-reef structure is lacking. Reef maintenance and growth is insufficient due to a shortage of oyster larvae and suitable settlement for oyster larvae. In regions with oyster aquaculture the lack of settled larvae limits oyster production, as farmers depend on the natural supply of larvae as starting material for aquaculture. Nature organizations, government and oyster farmers all agree that restoring an oyster reef can provide a solution. Still, there is mutual misunderstanding among stakeholders and a lack of knowledge about the successful combination of sustainable aquaculture and nature restoration.
Activities
Construction of a sublittoral flat oyster reef will take place in the Oosterschelde, the Netherlands. This former estuary and now protected natura 2000 area harbors a traditional oyster aquaculture community. Proposed activities include the selection of a suitable location and the actual construction of the reef. Monitoring of the (constructed) reef is an important part of this proposed project and will be conducted according to the BACI (Before-After, Control-Impact) approach. Monitoring will include oyster health parameters such as growth, survival, larval production and settlement, biodiversity indicators and the effect of management practices on both oyster health and biodiversity. Images collected using ROV and drop-down-camara (cf. zu Ermgassen et al., 2021) will be combined with observations by recreational divers (citizen science) and eDNA techniques for biodiversity monitoring,. A management plan will be drafted in consultation with all relevant stakeholders to ensure the sustainable survival of the constructed reef. All stakeholders in the consortium will be actively involved in all steps described.
Expected long-term changes
A permanent, self-sustaining sublittoral European flat oyster reef in the Oosterschelde providing ecosystem functions and services, notably habitat and larval supply;
A durable increase in the abundance of flat oyster larvae providing a reliable supply of juvenile oysters, ultimately enhancing flat oyster production in the area;
Commitment of oyster farmers for the maintenance and protection of the European flat oyster reef;
More knowledge and acceptance of the oyster farming practices, by stakeholders and society, providing a societal 'license to produce' for farmers, and thereby promoting low-tropic aquaculture.
The project serves as an example of successful coexistence of low-tropic aquaculture and nature restoration, validated by stakeholders, and communicated to society.
Consortium
HZ UAS as project and research coordinator, UAS Leiden, 6 Dutch oyster farmers, the oyster association, 3 nature organizations, 4 governmental bodies, and an organization coordinating citizen science.
References
Thomas, S., Collins, K., Hauton, C. and Jensen, A. (2022). A review of the ecosystem services provided by the native oyster (Ostrea edulis): implications for restoration. In IOP Conference Series: Materials Science and Engineering (Vol. 1245, No. 1, p. 012010). IOP Publishing. zu Ermgassen, P.S.E., Bos, O., Debney, A., Gamble, C., Glover, A., Pogoda, B., Pouvreau, S., Sanderson, W., Smyth, D. and Preston, J. (eds) (2021). European Native Oyster Habitat Restoration Monitoring Handbook. The Zoological Society of London, UK., London, UK.