Project: Feasibility Studies
Contact Person: Prof. Dr. Bela H. Buck
Status: finished
Open Ocean Aquaculture in Offshore Wind Farms
Study I
The feasibility (download study) study deals, on theoretical basis, with the potential multifunctional use of planned offshore-windfarms with commercial marine aquaculture (open ocean aquaculture) in the North Sea area. Exclusively, literature data from existing international experiences are reviewed here, as well as the output of several discussions with experts.
Firstly, the study reviews the current “state of the art” of open ocean aquaculture. The data was derived from existing projects within the international scientific community, which focused on candidate organisms, and dealt with offshore technology and maintenance aspects. Choice of location and infrastructure needed was also extracted from the findings of these projects. It became clear, that, in terms of commercial marine aquaculture, Germany, in comparison to many other maritime countries throughout the world, has to date little knowledge and background. Only one offshore aquaculture project nearby the Island of Helgoland was carried out. The current complicated and even counteractive national jurisdiction is identified being one of the main reasons for this lack of knowledge and experience. Next, the vast array of marine protected areas, national parks, as well as input of urban waste water adds to the calamity. However, especially the hydrodynamics of the North Sea play a key role as hindrance of establishing commercial marine aquaculture in Germany.
Secondly, the study carries out a selection of parameters, which need to be met during the decision-making of the location and construction of an offshore aquaculture farm. Next to geo-physical parameters, as wave parameters and local current profiles, other abiotic parameter, such as degree of contamination through urban waste water are addressed. Additionally, certain biological factors, such as plankton load and the concentration of chlorophyll within the possible locations were derived from existing data sets. A synthesis from these above parameters allowed the identification of suited candidates for a commercially running offshore-aquaculture. It is suggested to employ the cultivation of mussel (Mytilus edulis) and pacific oyster (Crassostrea gigas), as such a culture could be run extensively in the offshore region and the work-labour being mini mal. Similar accounts for seaweed, such as Laminaria saccharina and Palmaria palmata.
Thirdly, the study looked upon the possible selling market of the offshore aquaculture and their candidates in comparison to the performance of existing conventional operated farms in coastal waters. Main focus was placed on existing experience within the European community. It was put out, that a strong market exists for the suggested brown algae and red algae, which is likely to expand in the near future. The latter species can also be directly sold to the consumer as healthy food. However, one of the major elements for the economic success of the culture is the decision of the right location of an aquaculture. Here, factors like rapid accessibility due to shorter distances to the main land and available infrastructure need to be closely considered. Furthermore harbours with a good transport network and processing industries are, next to the direct local environmental factors at a specific wind farm, crucial factors. Thus, some of the wind farms, which are closer to the coastal areas economically more compatible as farm locations further off within the exclusive economic zone (EEZ). These factors, next to good management of the culture, are directly linked to the economic success of the activity.
The feasibility study closes with a final evaluation of all factors, which are critical for the development of a commercial offshore aquaculture in combination with the planned wind farms in the North Sea region.
Study II
The aim of this study (order study) was to identify scientific criteria and to acquire performance data for the development of mariculture in the context of sustainable multifunctional use of offshore space and natural resources.
In connection with current plans for a massive expansion of wind farms in offshore areas of the North Sea, the idea emerged to combine these with the installation of extensive mariculture for bivalves and macroalgae. Since offshore wind farms provide safety from shipping and infrastructure for attachment and service support, the opportunity for a multiple-use concept presented itself. However, prior to such a multifunctional development, it is necessary to determine the appropriate biological, technological and management requirements as well as the performance characteristics that would allow the employment of favourable and cost-effective methodologies. To this end, special focus was placed on the combination of extensive offshore shellfish and seaweed farming at exposed sites within the proposed offshore wind farms.
This thesis deals in detail with:
- the effects of abiotic and biotic factors on the growth potential of indigenous macroalgae and bivalves in extensive mariculture systems exposed to the stressful conditions of offshore habitats: (a) effects of physical forces on the cultivated species, (b) various parameters characterising the growth performance of species, (c) testing these parameters while using a variety of substrates and technical setups, (d) survival and health conditions, (e) recruitment, (f) parasite infestation of mussels in relation to inshore and offshore exposure, and (g) site-specific responses of the species to the various harsh offshore environments,
- the interaction between physical offshore processes and man-made structures in areas of the German North Sea territory where mariculture has potential,
- the conditions for possible combination of mariculture systems with offshore wind farms in terms of the legal framework and possible management strategies, and
- the socio-economic and legal consequences and interactions for offshore mussel farming with the existing conventional inshore bottom culture activities.
The research locations were specifically selected sites in the offshore region of the German Bight, mainly in the outer estuary of the River Weser, the offshore waters off the Island of Helgoland, several offshore areas where wind farms are planned, and habitats along the northern part of the Island of Sylt.
In this yet relatively young research field the performance of different offshore culture systems with attached macroalgae (Laminaria saccharina) and blue mussels (Mytilus edulis) was assessed at monthly sampling intervals. These procedures were carried out using research vessels, boats and scuba surveys, while determining morphometric parameters (e.g. length, width, thickness) as well as weight for growth analysis of mussels and seaweeds. Furthermore, the condition index, the meat content and the degree of parasite infestation of blue mussels were determined. The abundance of mussel larvae in the water column and the resulting settlement success of post-larvae on various spat collectors were investigated. Seaweed studies included attachment strength, breaking and drag forces on kelp sporophytes in order to describe the resistance of cultivated Laminarians to high-energy environments. Additional assessment criteria were biochemical parameters (e.g. nutrient-, chlorophyll-, POC- and TON-concentrations and their ratios) to describe the food availability for mussels and the nutrient composition for algal growth as well as oceanographic parameters (currents, waves, swell, salinity, temperature, light attenuation) to describe the wave climate and current velocities of the study sites in the offshore environment. Technical studies comprised two system designs (longline, ring structure) of various set ups (submerged or floating mode) in different locations (offshore or inshore) to find an appropriate culture design to sustain growth and survival of cultivated species. Further, a specially designed offshore spat collector was used for settlement investigations of mussel post larvae. Some fundamental studies were carried out in order to pave the way for the realisation of open ocean aquaculture in offshore wind farms (e.g. multifunctional use of offshore habitats in terms of avoidance of stakeholder conflicts, the legal framework for such activities in coastal areas and in the Exclusive Economic Zone, the multi-use concept in terms of integrated coastal zone management).
Laminaria saccharina showed sufficient length increments in offshore habitats growing on a submerged ring system. It could be demonstrated by drag and breaking-/dislodgement force experiments that algae were capable of resisting the high-energy environment of the North Sea. The concentration of mussel larvae in the water column decreased offshore and resulted in a low settlement success while at the same time infestation load decreased and was lacking at offshore suspended collectors. The three system designs showed different results. While the offshore ring proved to be superior for seaweed cultivation under the harsh conditions, the longline showed some major drawbacks in terms of materials used, design and installation modes (submerged or floating). The spat collector largely withstood the harsh hydrodynamic conditions of the North Sea. The hitherto fragmented legal framework for the offshore waters was found to be one of the key constraints for the successful implementation of multifunctional use schemes. However, participation of all involved stakeholders may provide a window of opportunity to turn the existing lack of offshore regulations into a positive momentum, as scope exists to move with the development of new offshore co-management concepts beyond existing management approaches.
Whether such offshore installations would provide sufficient economic returns could not be answered yet, as experience on the maintenance of offshore wind farms is lacking so far.
However, the discovery that Laminaria saccharina resists offshore forces and shows sufficient length increments and mussels growing in offshore habitats are not affected by parasites may provide a key incentive for positive commercial use.
It thus can be shown that there is a high potential for farming the “deep blue” in the German EEZ, provided that some of the constraints, of which the lack of legal framework and technical aspects seems to be most severe, are resolved in the near future.