Description: Drawing on a case study in Germany, this contribution explores the practical application of offshore aquaculture within offshore wind farms in view of the different stakeholders involved. Using a transdisciplinary research approach, an understanding of the rationalities and interests among the different involved stakeholder groups was explored. Offshore wind energy is high on the political agenda in Germany. The vast spatial requirements however inherit potential user conflicts with competing, and under current legislation excluded users such as fishermen. Solutions for combining sustainable uses of the same ocean space have thus seen increasing interest within the research community in Germany and in Europe over the past years. This paper was inspired by and presents the outcomes of a stakeholder analysis and in particular a stakeholder workshop. Central focus was placed on academics and private as well as public stakeholders engaged in current research efforts of combining offshore wind farms and aquaculture in the German North Sea. The paper identifies the overall acceptance of such a multi-use scenario in society, opportunities and constraints as perceived by the stakeholders, and key research gaps. The results confirm the assumption that there is a clear need, and also willingness on behalf of the policy makers and the research community, to find sustainable, resource- and space-efficient solutions for combined ocean use.

Description: Aquaculture is projected to be a major supplier of marine proteins to large parts of the global population. This includes bivalves, which have a high potential to offset protein deficits, as they are highly adaptable to varying water temperature, salinity, desiccation, and oxygen conditions. This work is part of a two-piece contribution on novel marine aquaculture technology and details physical laboratory tests of a new cultivation system for bivalve farming called “Shellfish Tower”. The tested 1:20 model consists of a rectangular cage (2 × 2 m prototype scale) with a central buoyancy element and a height of 2 – 4 m. Testing was done in a current flume as well as a wave basin for current velocities between 0.4 – 2.2 m/s and wave heights of 1.6 to 5.0 m with periods between 5 to 14 s. The tests were conducted to prove the feasibility and functionality of this aquaculture system, which is usable for the collection and cultivation of mussel spat as well as for the grow-out of oysters, scallops, and seaweed in marine environments. Tests carried out in a current flume revealed that drag coefficients decrease with increasing current velocities, and range from Cd=0.5 to 2.5, while the mooring inclination increases from 12° to 84° with increasing flow velocity, which is highly dependant on the buoyancy related pretension. The examination of the mooring line tensions recorded in a wave basin showed that the largest values of snap-induced tension were up to 10 times that of the semi-static tension. The maximum-recorded tension on the system was 48 kN for a single and 89 kN for a double configuration, compared to non-snap tension values, which were in the range of 6 – 10 kN. The insights gathered in this study will inform the future design of aquaculture systems in high-energy environments and allow for an integration into numerical models.

Description: The purpose of this publication is to perform a system analysis of new cultivation technology for exposed bivalve farming. The technical feasibility of the new construction, called Shellfish Tower, was assessed. The device has gone through several very different phases of development on its way to the deployment of the prototype. These included multiple iterations during the designing stage, wave tank testing, fabrication, loading and unloading on trucks and vessels, deployment at sea, installation and assembly on the single mooring line, and bring it to its final position in a submerged mode 5m-10 m below the water surface. The final structure has a hexagonal body, with a centrally orientated variable buoyancy unit with culture sub-units on each of the six corners. These sub-units can be used for the culture of oysters (Magallana gigas – formally Crassostrea gigas) as well as for the collection of mussel spat (Perna canaliculus). Other possible candidates could be seaweed, lobsters, sponges or tunicates. The operational depth of the whole system can be at any depth but was tested at between 5 and 10 m below the water surface positioned on the mooring line between the screw anchor and surface floats for the prototype tests. The system was deployed in March 2019 six nautical miles off the Bay of Plenty, North Island (New Zealand), in exposed waters near a commercial mussel farm and has been in test mode since then. The modelled structure indicates a design tolerance of significant wave height of over 7 m and currents of over 0.8 m/s. Initial results show that the new design has survived waves at 4.6 m significant height and current velocities of up to 0.7 m•s-1, while showing best growth conditions of the cultured oysters as well as for the spat settlement of juvenile greenshell™ mussels.

Description: There is growing interest in using recirculating aquaculture systems (RAS) to raise noble crayfish Astacus astacus a valuable and once plentiful food species in Europe, now a highly endangered species. The growth and survival of A. astacus was compared in growth trials in RAS and open-pond systems (OPS) over a period of 2 months. Energy and lipid content of available diets and crayfish tissue were also determined. Growth of A. astacus during summer was significantly (p 〈 0.01, one sample t test) higher in OPS (SGR 1.23) than in RAS even at the highest feeding ration provided at 5 % bw/d−1 (RAS HI SGR 0.78 ± 0.06). OPS crayfish also had significantly (p 〈 0.01 OPS vs. all RAS treatments; Pairwise Wilcoxon) higher lipid content (8.51 %) than RAS crayfish (RAS HI 5.73 %, RAS MED 6.93 %, RAS LOW 5.92 %). Survival rates in RAS were, however, 100 % compared with previous observations in OPS of approx. 70 %. While results showed OPS growth exceeds than that in RAS in the short term, RAS survival rates and annualized growth performance may outweigh this disadvantage, particularly if optimal artificial diets for RAS holding are provided. Feed and crayfish analysis indicated that culturing A. astacus in RAS require a diet protein content exceeding 30 % and lipid content of 〈13 %, indicating that the carp diet supplied was not optimal. RAS culture allows this valuable species to be cultured in controlled, disease-free enclosed systems—resulting in high-value food products as well as high-quality seedlings for restocking purpose.

Description: Drawing on a case study in Germany, this contribution explores the practical application of offshore aquaculture within offshore wind farms in view of the different stakeholders involved. Using a transdisciplinary research approach, an understanding of the rationalities and interests among the different involved stakeholder groups was explored. Offshore wind energy is high on the political agenda in Germany. The vast spatial requirements however inherit potential user conflicts with competing, and under current legislation excluded users such as fishermen. Solutions for combining sustainable uses of the same ocean space have thus seen increasing interest within the research community in Germany and in Europe over the past years. This paper was inspired by and presents the outcomes of a stakeholder analysis and in particular a stakeholder workshop. Central focus was placed on academics and private as well as public stakeholders engaged in current research efforts of combining offshore wind farms and aquaculture in the German North Sea. The paper identifies the overall acceptance of such a multi-use scenario in society, opportunities and constraints as perceived by the stakeholders, and key research gaps. The results confirm the assumption that there is a clear need, and also willingness on behalf of the policy makers and the research community, to find sustainable, resource- and space-efficient solutions for combined ocean use.

Description: The concept of co-location of marine areas receives an increased significance in the light of sustainable development in the already heavily used offshore marine realm. Within this study, different spatial co-location scenarios for the coupling of offshore aquacultures and wind farms are evaluated in order to support efficient and sustainable marine spatial management strategies. A Geographic Information System (GIS) and multi-criteria evaluation (MCE) techniques were combined to index suitable co-sites in the German exclusive economic zone of the North Sea. The MCE was based on criteria such as temperature, salinity or oxygen. In total, 13 possible aquaculture candidates (seaweed, bivalves, fish and crustaceans) were selected for the scenario configuration. The GIS modelling framework proved to be powerful in defining potential co-location sites. The aquaculture candidate oarweed (Laminaria digitata) revealed the highest suitability scores at 10–20 m depth from April to June, followed by haddock (Melanogrammus aeglefinus) at 20–30 m depth and dulse (Palmaria palmata) and Sea belt (Saccharina latissima) at 0–10 m depth between April and June. In summary, results showed several wind farms were de facto suitable sites for aquaculture since they exhibited high suitability scores for Integrated Multi-Trophic Aquaculture (IMTA) systems combining fish species, bivalves and seaweeds. The present results illustrate how synergies may be realised between competing needs of both offshore wind energy and offshore IMTA in the German EEZ of the North Sea. This might offer guidance to stakeholders and assist decision-makers in determining the most suitable sites for pilot projects using IMTA techniques.

Description: In the offshore region of Germany, human activity is increasing in type and intensity. Larger portions of the sea are sectioned off, dedicated for specific, often exclusive uses that cause rising conflicts between interests groups. One solution calls for stakeholder integration and the multifunctional use of space. This article focuses on two examples, offshore wind farms and open ocean aquaculture. It analyses their potential synergies within a co-management approach. It can be shown, that an integrated co-management strategy for offshore regions requires very different sets of rights and duties, as well as holding different types of conflicts, constrains and alliances, some of which are illustrated for the presented case study. The article closes with the conclusion that an integrated regulative framework is the most important basic precondition for a multifunctional utilisation of offshore areas and its sustainable development.

Description: Offshore waters are in a process of transition, revealing diverse and heterogenic interests in marine resources. This increasing complexity leads to limits in developing and managing the different and often spatially overlapping maritime activities independently of one another. On a showcase basis we discuss ways and manners as well as the preconditions of an offshore co-management approach for the fledgling actor groups offshore wind farmers and mariculturists. Both groups may benefit through the integration of operation and maintenance (O&M) activities. Their resources in terms of offers, needs and constraints characteristics and thereof deduced potentialities for interaction is a prerequisite for initiating a co-management process. This process is more likely to develop and succeed if an interface management that acts as a moderator, disclosing the interests of the actor groups and offering possibilities for concerted action, guides it. It is concluded that such an institutional arrangement may in the long term contribute to a sound methodological tool for a co-management approach between different offshore maritime sectors.

Description: Using a comprehensive approach, intertidal, near- and offshore sites in the German Bight were analysed for their environmental quality by assessing the health of blue mussels (Mytilus edulis). During a ten month sampling period mussels were studied with a set of biomarkers comprising lysosomal membrane stability and accumulation of lipofuscin, supplemented by biomarkers indicating nutritional status such as neutral lipids and glycogen in the cells of the digestive gland. Data were analysed in relation to sex, gonadal status, condition index and for the presence of parasites, to determine the overall health status of mussels at the respective sites. Mussels from all sites showed clear signs of stress, indicating an inferior environmental quality throughout the southern German Bight. Further, habitat characteristics such as inundation time and growing on- or off-bottom, as well as seasonal factors, can clearly influence the response of biomarkers in mussels exposed to similar levels of chemical environmental stress.