Description: By moving away from coastal waters and hence reducing pressure on nearshore ecosystems, offshore aquaculture can be seen as a possible step towards the large-scale expansion of marine food production. Integrated multi-trophic aquaculture (IMTA) in nearshore water bodies has received increasing attention and could therefore play a role in the transfer of aquaculture operations to offshore areas. IMTA holds scope for multi-use of offshore areas and can bring environmental benefits from making use of waste products and transforming these into valuable co-products. Furthermore, they may act as alternative marine production systems and provide scope for alternative income options for coastal communities, e.g., by acting as nodes for farm operation and maintenance requirements. This paper summarizes the current state of knowledge on the implications of the exposed nature of offshore and open ocean sites on the biological, technological and socio-economic performance of IMTA. Of particular interest is improving knowledge about resource flows between integrated species in hydrodynamic challenging conditions that characterize offshore waters.

Description: This review summarizes the recent literature on the biology, cultivation techniques and uses of the red seaweed Palmaria palmata ((Linnaeus) Weber & Mohr 1805). The paper covers its distribution, appearance and life cycle, the state of the art cultivation techniques for spore release and seeding, and the culture of meristematic fragments of fronds harvested from natural populations. Furthermore, culture conditions for P. palmata sporelings and gametophytes and set-ups of tank and open sea culture are presented. For tank culture, relatively high irradiance and frequent seawater exchange to supply carbon dioxide and nutrients are the most important parameters. In open sea culture, site selection and system design play an important role. Land-based culture has the advantage that optimum culture conditions can be applied and quality-controlled, whereas nearshore cultivation is less costly and labour intensive. In addition, the bioremediation potential and the use of P. palmata in integrated multitrophic aquaculture (IMTA) are discussed. More research is needed to investigate bioremediation potential of different P. palmata strains. Recent developments in uses of P. palmata as food supplement, source of bioactive compounds, animal feed and compound for biofuels are presented. Finally, the possibilities of cultivation of P. palmata enhance the prospects for the expansion of the cultivation of this seaweed. However, future research is needed regarding balance of culture conditions, costs and biomass in land-based tank culture and in terms of site selection, system design, maintenance and harvest techniques in sea cultivation to establish a commercialization of the aquaculture of this species in Europe.

Description: The concept of multifunctional use of marine offshore areas receives increased significance in the light of sustainable development in heavily used marine areas. Here we defined potential areas in the German EEZ for the co-utilization of offshore wind farms and offshore aquaculture applying integrated multi-trophic aquaculture (IMTA) approaches. We combined a geographic information system (GIS), spatial distribution models and multi-criteria evaluation (MCE) to index suitable multifunctional sites. The procedure as well as the main findings of the GIS-MCE modelling approach are summarised to demonstrate the applicability of the GIS-MCE and the need for modelling techniques for spatial optimisation using geo-spatial tools. Finally, different spatial multi-use scenarios for the coupling of offshore IMTA-systems and wind farms are evaluated in order to support efficient and sustainable marine spatial management (MSP) strategies.

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: Most studies on multi-use concepts of aquaculture and wind farms explored cultivation feasibility of extractive species, such as seaweed or bivalves. However, recent studies also included the cultivation of crustaceans or fish culture in the vicinity of wind turbines. Consequently, new approaches combine fed and extractive species in integrated multi-trophic aquaculture (IMTA) concepts for offshore multi-use to reduce nutrient output and the overall environmental impact of aquaculture operations. In this chapter the findings of a series of mussel and oyster cultivation experiments over several seasons are presented, which were conducted at different offshore test sites in the German Bight. Sites were selected within future offshore wind farm areas for an explicit multi-use perspective. Results have demonstrated successful growth and fitness parameters of these candidates and therefore definitely proved the suitability of these bivalve extractive species for open ocean aquaculture. Another approach for multi-use in offshore wind farms is its use as marine protected area or even for reinforcement or restoration of endangered species, which need the absence of any fisheries activity for recovery. Current projects are testing this perspective for the native European oyster Ostrea edulis and the European lobster Homarus gammarus. From the technological point of view there are many options on how to connect aquaculture devices, such as longline and ring structures as well as different cage types, to the foundations as well as to install it in the centre of the free area between wind turbines. Next to the system design also experiments on drag forces originating from the aquaculture structure on the foundation and vice versa were investigated. Complementary to the biological, environmental end technical aspects, a number of studies were specifically targeted to address and include stakeholders, their attitudes, their interests and concerns over time. By this approach, the inclusion of stakeholders into the research process from its very beginning until today, co-production of knowledge could be fostered. Next to joint identification of the major impediments and concerns of offshore aquaculture under multi-use conditions, new issues and research questions were identified. Primary focus on the economic potential of aquaculture in offshore wind farms was shown for consumption mussels. The production of mussels using longline technology is sufficiently profitable even under the assumption of substantial cost increases. This is especially true, if existing capacities could be used. Last but not least, the EEZ is a special area—it is not a state territory even if a coastal state has its sovereign rights and jurisdiction. It is an area where three legal systems come together: international law, law of the European Union and national law. There are no mariculture projects in the German EEZ and no approval procedure has been completed so far. Some sites are not suitable for mariculture, especially because of nature conservation and shipping.

Description: The bioremediation capacity of the red macroalga Palmaria palmata was assessed by two experiments. First, uptake rates of P. palmata cultured in four treatments with varying levels and ratios of the N sources ammonium (NH4 +) and nitrate (NO3 −) (18/15, 0/30, 30/45, 50/65 μM) were measured over a 3-h period to evaluate N source preference. Secondly, P. palmata were cultured in five treatments with varying levels and ratios of ammonium and nitrate (300/12, 0/312, 500/12, 0/512, 250/262 μM) for 3 weeks to evaluate specific growth rates, protein content, and ammonia toxicity. Palmaria palmata had a higher affinity for NH4 + than for NO3 − as N source. However, in the single N source trials, NO3 − uptake was higher than that of NH4 +. The maximum specific growth rate of 11.99 % day−1 was observed in the 0/512 μM ammonium/nitrate treatment after 3 weeks, whereas the minimum specific growth rate of 2.21 % day−1 was observed in the 500/12 μM ammonium/nitrate treatment after 3 weeks. NO3 − supported higher growth rates, whereas NH4 + increased tissue N, and therefore protein content. Total protein content of the algal tissue was significantly higher in P. palmata of the NH4 + treatments, reaching up to 20.6 % DW, than of those from the NO3 -treatments. Palmaria palmata showed signs of poisoning after 3 weeks in the highest NH4 + treatment. This study indicates that P. palmata is a suitable species for ecological engineering in integrated multitrophic aquaculture systems as it shows a relatively high growth performance, high nutrient uptake rates, and elevated protein content under NH4 + supply.

Description: The concept of multifunctional use of marine offshore areas receives increased significance in the light of sustainable development in heavily used marine areas. Here we defined potential areas in the German EEZ for the co-utilization of offshore wind farms and offshore aquaculture applying integrated multi-trophic aquaculture (IMTA) approaches. We combined a geographic information system (GIS), spatial distribution models and multi-criteria evaluation (MCE) to index suitable multifunctional sites. The procedure as well as the main findings of the GIS-MCE modelling approach are summarised to demonstrate the applicability of the GIS-MCE and the need for modelling techniques for spatial optimisation using geo-spatial tools. Finally, different spatial multi-use scenarios for the coupling of offshore IMTA-systems and wind farms are evaluated in order to support efficient and sustainable marine spatial management (MSP) strategies.

Description: The purpose of this study was to investigate the effectiveness of 11 different culture media for production of the free-living nematode Turbatrix aceti. Several other harvesting methods were tested in addition to mass production. A further focus was the investigation of amino acid alterations caused by the application of various media during the culture of T. aceti and two additional nematode species, Panagrellus redivivus and Caenorhabditis elegans. Finally, a cost analysis for the production of T. aceti was generated and its outcome compared to the production of conventional live feed organisms. Altogether 11 liquid culture media were tested for mass production of the nematode Turbatrix aceti using a minimum of effort in terms of labour and costs. Six harvesting methods, including filtration as well as active swimming of T. aceti were evaluated. Additional to the culture of T. aceti in four of the above-mentioned media, the nematodes P. redivivus and C. elegans were cultured on two different solid media. Cost analysis for the production of T. aceti includes those of the media, the equipment, as well as the labour costs for culture and harvest. An average density of approx. 30 × 106 ± 8.13 × 106 nematodes L−1 was achieved for T. aceti. The most efficient method (20 μm filtration) allowed harvesting 85.3 ± 2.7% of the nematodes from the medium without disturbing the particles. Lowest efficiency was achieved by combining sedimentation and filtration, accomplishing a harvest of 42.1 ± 5.8%. The amino acid profile of all three nematode species turned out to be both stable and very similar. Amino acid enrichment had little effect. The costs for producing one million T. aceti individuals ranged between 5.39 and 6.19 €, where labour costs accounted for 73 to 84% of the total production costs. In conclusion, T. aceti appears to be very robust, easy to handle, as well as cheaper to cultivate compared to other live-feed organisms. Therefore, its use in commercial aquaculture should be given future consideration.

Description: By incorporating the free-swimming nematode Turbatrix aceti into early feeding regimes of the European whitefish Coregonus maraena, the suitability of this nematode species was investigated as an alternative to Artemia nauplii. During a 14-day feeding trial in a total of 25 aquaria each 1.7 L (each treatment n = 5, 255 larvae/tank) T. aceti was used either as the sole live food or in combination with Artemia nauplii or microdiet to determine the effect of T. aceti on growth performance and survival rate of C. maraena. By analysing the fatty acid composition of T. aceti prior to and after enrichment with INVE spresso® it was investigated whether the amount of n3-polyunsaturated fatty acids (n3-PUFA) in T. aceti could be further enhanced. Supplementation of Artemia nauplii with T. aceti increased growth significantly within the first 5 days of rearing in comparison to the non-supplemented food treatments (14.39 ± 0.15 mm compared to 13.44 ± 0.18 mm; mean ± SE). However, growth and survival of juvenile C. maraena on nematode-supplemented Artemia nauplii did not differ significantly from non-supplemented Artemia nauplii at the end of the 14-day rearing period (15.22 ± 0.15 mm compared to 14.86 ± 0.24 mm). All feeding treatments containing Artemia nauplii showed significantly higher growth and lower mortality at the end of the experiment in comparison to diets containing only the microdiet or T. aceti or a combination thereof. The overall low performance of T. aceti alone can most likely be explained by an insufficient capacity of C. maraena to digest this nematode species efficiently. Enrichment with INVE spresso® successfully increased the proportion of DHA in the T. aceti tissue. The results reveal that T. aceti cannot be considered a full alternative to Artemia nauplii, at least not in the rearing of C. maraena, but might be a useful vector of essential fatty acids within the early rearing period of this and potentially other fish species when provided as live food along with Artemia nauplii.