Introduction
Oyster beds and reefs provide essential ecosystem functions within coastal and offshore ecosystems around the world, providing structural complexity leading to numerous ecosystem services, as well as contributing to coastal economies for centuries (Beck et al., 2011). As such, they are the focus of several flat oyster nature-based solution projects, restorative flat oyster aquaculture projects (Carranza & Zu Ermgassen, 2020) and a multitude of habitat creation or restoration projects in almost all countries border the North Sea or the English Channel (https://noraeurope.eu).
Methods
A DEB-IBM (Dynamic Energy Budget - Individual Based Model) population model was coupled with the LARVAE&CO larvae dispersal model. The DEB-IBM is a bioenergetics-based population model (Stechele et al., 2023). The LARVAE&CO model is an IBM that simulates egg and larval dispersal. This work establishes a population model for flat oyster population dynamics and dispersal and applies the model to the English Channel and the North Sea to indicate suitability for offshore flat oyster habitat restoration and restorative aquaculture.
Suitable locations for restorative aquaculture are indicated by quantifying suitability indicators including population increase, fitness, reproductive potential, self-recruitment and sediment suitability.
Results
Restoration hotspots (total suitability indicator score = 4) are located in the Wash (UK), all along the coast of East England and the outer Thames estuary (UK), in the offshore mid Channel south of the Island of Wight, around the Isle of Wight (UK), all along the coast of Dorset and Devon (UK), all along the coast from Saint-Brieuc (FR) to Le Mont-Saint-Michel (FR), Côte Fleurie (FR) all along the coast of Haute Normandy from Fécamp to Le Tréport (FR), around Dunkerque (FR), in the Northern parts of the Scheldt Estuary (NL), off the coast of Noord-Holland (NL), in and around both the Western and Eastern Frysian Islands (DE) and around Helgoland (DE).
Suitability indicators scores can be linked to the occurrence of historical beds.
Conclusion
The English Channel is highly suitable for flat oyster restorative aquaculture (both nearshore and offshore). In offshore locations of the North Sea, we do not expect to see high population increases due to colocation of flat oyster aquaculture and restoration, and restorative aquaculture efforts should be scaled up, to boost larval production and recruitment. To increase success of flat oyster habitat restoration in the offshore environment, we suggest the implementation of a basin-wide coordinated restoration effort that promotes the connectivity between natural oyster beds, restoration sites, oyster NID developments and aquaculture sites.
References
Beck, M. W., Brumbaugh, R. D., Airoldi, L., Carranza, A., Coen, L. D., Crawford, C., ... & Guo, X. (2011). Oyster reefs at risk and recommendations for conservation, restoration, and management. Bioscience, 61(2), 107-116.
Carranza, A., & Zu Ermgassen, P. S. (2020). A global overview of restorative shellfish mariculture. Frontiers in Marine Science, 7, 722.
Stechele, B., Hughes, A., Degraer, S., Bossier, P., Nevejan, N. (2023). Northern Europe’s suitability for offshore European flat oyster (Ostrea edulis) habitat restoration: A mechanistic niche modelling approach. Aquatic Conservation (in press). https://doi.org/10.1002/aqc.3947