Engineering nature-inclusive marine infrastructure with an emphasis on flat oyster reef development in offshore wind farms in the Southern North Sea

Abstract

Rapid changes in the marine environment are taking place worldwide, for which infrastructural development is one of the most extreme anthropogenic drivers. It comes in many forms and covers functionalities for multiple usages, such as coastal defence, transportation, and energy production. Marine infrastructure modifies seascapes by replacing natural habitats and changing environmental conditions critical to habitat persistence, potentially leading to its degradation and biodiversity loss. Although primarily built to meet functional criteria, their designs can incorporate nature-inclusive elements that benefit ecosystem components, i.e. species, habitats or ecosystem processes.

The implementation of nature-inclusive marine infrastructure is increasingly encouraged, but currently fails to achieve impact at scale due to the fragmented nature of individual measures. Without shared objectives, parallel efforts to enhance targeted ecosystem components might not lead to the desired effect, and could even interfere with each other. A jointly established strategy is required to design and implement nature-inclusive marine infrastructure that meets the wanted impact. Such as strategy is based upon overarching objectives for promoting selected ecosystem components at system-scale, i.e. the seascape dimension required to achieve the desired effect. It is furthermore essential to determine and develop design measures that would induce impact and to define the scale needed for these interventions. It is recognized that marine construction works first serve human needs, not nature goals, but nature-inclusive marine infrastructure does provide an opportunity to benefit ecological values at system-scale. Marine construction works can be synergized with the functioning of the ecosystem in which they are build much better than is currently practiced, and one should always strive for nature-inclusive features in their designs.

This dissertation provides insight into the process to identify, select and implement measures for nature-inclusive marine infrastructure to make a desired impact at system-scale, i.e. the seascape dimension required to achieve that impact. First, a stepwise approach is presented to define clear objectives for improving targeted ecosystem components, in which ruling polices, environmental conditions and the potential of using marine infrastructure are aligned. Stakeholders jointly select the most effective design measures for nature-inclusive marine infrastructure to reach shared targets for ecological impact. Next, it is key to define the scale of these interventions needed to achieve significant impact. A method is developed to select appropriate measures to benefit ecosystem components at a range of scales, from micro-scale (materials used) to mega-scale (connectivity between systems), and to assess their potential effects quantitatively. And finally, it is emphasized that nature-inclusive marine infrastructure can only make impact at system-scale if scientific knowledge about ecosystem functioning is paired with industry-based approaches used for infrastructural development. Five basic principles are provided for establishing this alignment, in order to effectively implement nature-inclusive design measures.

The approaches for engineering nature-inclusive marine infrastructure are demonstrated by defining a strategy to develop European flat oyster (Ostrea edulis) reefs in offshore wind farms in the Southern North Sea. The huge roll out of offshore wind farms aimed at renewable energy production in the North Sea is currently one of the most prominent marine infrastructural developments globally. Its potential for promoting targeted ecosystem components is recognized, as offshore wind farms provide an undisturbed seabed as well as hard substrate infrastructure, which both provide suitable habitat for a wide range of marine organisms. The results of a dedicated monitoring survey in existing offshore wind farms show that their presence indeed contributes to an increase in marine epibenthic biodiversity. Using the offshore wind farm areas specifically for the development of flat oyster reefs has gained particular interest. This species went near to extinct in the 20th century due to overfishing and diseases, and restoring flat oyster reefs in the North Sea meets international policy agreements. Offshore wind farms can be designed to include elements that benefit the restoration of this flat oyster population, such as using a type of hard substrate as scour protection that is favourable for oyster larvae settlement.

In conclusion, this dissertation provides guidance for defining management strategies for implementing nature-inclusive marine infrastructure to achieve impact at system-scale, with an emphasis on flat oyster reef development in offshore wind farms in the Southern North Sea. Application of the presented methods and outcomes of the studies could lead to the realisation of truly effective nature-inclusive marine infrastructure, seizing the opportunity offered by infrastructural developments to have a positive impact on the marine environment.