Design for biodiversity: Enhancing biogenic shellfish reefs

Abstract

Biogenic reefs built by mussels, oysters or other reef-building species are one of the most important biodiversity hotspots for estuarine and marine ecosystems providing food, shelter, and breeding grounds for a wide array of species. In the North Sea, one of the most important biogenic reef builders and ecosystem engineers is the European Flat Oyster. However, due to harmful fishing practices, habitat destruction and diseases, this once-abundant bivalve is now ecologically extinct and cannot provide crucial ecosystem services. If left without active intervention, oyster reefs have too few chances of regeneration, due to the current state of the seafloor in the North Sea and too few individuals in the environment. Therefore, active intervention is needed to bring back the shellfish reefs in The North Sea. Offshore windmill farms provide a refuge for marine ecosystems from fishing activities, which poses an important opportunity for biogenic reef restoration practices.

To understand the context of biogenic reef restoration better, multiple interviews with marine biology and ecology experts from ARK were conducted followed by a literature review and two field trips related to young oyster deployment to The North Sea. The gained insights were used to create a list of 12 design criteria grouped into four categories: Oyster survival, Scalability, Broader ecological success, Handling & deployment. According to these criteria, most of the current practices underperform in scalability due to high manufacturing, and operational costs, or provide inefficient oyster protection which hampers the success of shellfish reef restorations. Therefore, the design challenge to improve scalability and oyster protection has been chosen as the priority.

Multiple design directions and ideas have been explored using Research by Design approach while employing Whole System Mapping and Biomimicry methods with Low- and high-fidelity prototypes. Using an iterative approach and evaluating the design ideas, the solution space has been narrowed down to a final design, the unit: two steel frame gabions are connected in a double-diamond position and placed between two display pallets with all assembly tightly secured with a cotton lashing. Multiple assemblies are connected in a row with a leading rope attached to an anchor. When the ship sails, the anchor is thrown out on the seafloor and eventually pulls all units down to the seafloor. The final design was evaluated according to the same 12 criteria. In comparison to previously discussed solutions, the final design is more scalable in terms of costs and time for larger marine restoration areas and focuses on finding balance throughout the design criteria instead of being only effective in certain aspects. In addition to introducing back the Flat Oysters, the new structures provide various microhabitats for a wide array of other benthic species to grow or shelter from the water currents, amplifying positive effects on the marine ecosystem. Several theoretical and structural integrity tests have been done to determine the effectiveness of the new design. Further research, such as offshore field studies, is needed to determine how this new design affects young oyster survival and other benthic species.