NEW CONCEPT COMBINES OFFSHORE WIND FARMS AND MUSSEL CULTIVATION
2. First Results
Initial trial results showed that the basic biotic conditions in many parts of the German North Sea support the cultivation of mussels under harsh conditions. Food availability and quality, and larval supply are sufficient. The blue mussel, Mytilus edulis, showed excellent growth rates and reached market size within a season and a half (Buck 2007, Walter et al. 2010) (Fig. 2). Furthermore, modified and improved offshore culture techniques can now withstand the environmental forces of the North Sea. However, these new constructions could certainly raise investments costs. All such relevant site selection criteria of potential culture plots should be well known to calculate economic risks.
Chapter 05 Offshore wind farms and mussel cultivation 39
Fig. 2: In trials, blue mussels reached market size within a season and a half.
2.1. Parasitic Infestations
Research also showed that macro parasites would be an important consideration. Although all known macro parasite species of blue mussels are considered harmless to human consumers, obviously infested mussels lose their economic value. For example, the parasitic copepod Mytilicola intestinales is bright red in color, and at up to 10 mm in length, easily visible (Fig. 3). It is simply an aesthetic problem. Interestingly, mussels grown offshore are free of macro parasites, in contrast to bottom-grown mussels in nearshore areas (Buck et al. 2005). The complex life cycle of parasitic trematodes is only completed near shore, where mussels, periwinkles, and sea birds live in close communities.
Other parasitic copepods need the long-living natural beds of blue mussels to develop and establish their populations.
Infestations with micro parasites and viruses may follow the same pattern, but in contrast to their larger counterparts, infestations with viruses can provide serious risks to the health of cultured candidates. Although the life cycles of common micro parasites like Bonamia or Marteilia species are still unknown (OiE 2003), their abundance might also be connected with the natural mussel beds nearshore.
Chapter 05 Offshore wind farms and mussel cultivation 40
Fig. 3: Although harmless to humans, the brightly colored Mytilicola intestinales copepod that affects mussels is easily visible.
2.2. Water Quality
One can assume that offshore areas have lower concentrations of pollutants, pesticides, and near-surface agents due to dilution of urban sewage and estuarine runoffs. In fact, offshore areas provide a maximum supply of clean water with good dissolved-oxygen conditions. Mussels grown under such conditions accumulate fewer toxins and would likely have less stressed immune systems and better overall health than mussels grown in near- and inshore areas. As shown by various European research institutes, these factors result in higher growth rates and yield a qualitatively better product for human consumption.
2.3. Biodiagnostic Tools
In a new approach, the authors are using modern biodiagnostic tools to quickly and inexpensively analyze site conditions and the overall health of mussels cultured in different offshore areas (Cajaraville et al. 1998). With these methods, the tissue of the mussels’ digestive systems responsible for food uptake, storage of reserve substances, and detoxification provides a clear signal on the health status of the mussels. For example, the condition of the surrounding membranes of lysosomes is tested. Lysosomes are usually responsible for the recycling of other spent cell organelles and metabolic products, as well as harmful substances that enter the cells. When the storage capacities of lysosomes are overloaded, and cells are stressed by high concentrations of harmful substances, the lysosomal membranes can become unstable and pollutants leak back into the cytoplasm with serious risk for health (Koehler et al. 2002). If membrane stability and the overall health status of mussels are low, more specific tests can elucidate the types and backgrounds of the causal pollution. In contrast, if lysosome membranes are stable, there is strong evidence that individual mussels grow under good water conditions (Brenner et al. 2006).
Chapter 05 Offshore wind farms and mussel cultivation 41
2.4. Targeted Sites
The implementation of biodiagnostic methodologies to identify potential culture areas within the zones proposed for offshore wind farms is one focus of the new MytiFit project financed by the Ministry for Construction, Environment, and Transport in Bremen, Germany, and the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. Other aspects include the quantification of micro and macroparasites, shell stability, and the attachment strength of mussels using different artificial substrates. In a test field located in the vicinity of a planned offshore wind farm about 31 km off the coast at Bremerhaven, three test moorings with large buoyancy will be deployed to test the described parameters in different water depths (Fig. 4). The aim of the project is to accumulate relevant information for the selection of appropriate cultivation sites for mussels in the planned wind farm areas. The prediction of rapid growth and high product quality should compensate for the higher investment costs of the culture systems and help install a functioning offshore aquaculture system in the German Bight (for more details refer to Buck et al. 2007).
Fig. 4: One element of the MytiFit project involves an evaluation of blue mussel attachment to varied artificial substrates that could be used for culture at offshore wind farms.
Chapter 05 Offshore wind farms and mussel cultivation 42
References
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Buck BH (2002). Open Ocean Aquakultur und Offshore-Windparks. Eine Machbarkeitsstudie über die multifunktionale Nutzung von Offshore-Windparks und Offshore-Marikultur im Raum Nordsee.
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Buck BH, Koehler A, Brenner M, Stede M (2008). Eignung des Seegebietes am geplanten Offshore-Windpark Nordergründe für die Zucht von Miesmuscheln: Fitness, Parasitisierung und Substratwahl. Endbericht, 91 pp
Cajaraville MP, Cancio I, Orbea A, Lekube X, Marigómez I (1998). Detection, control and monitoring of pollution using early warning cellular biomarkers: conventional and innovative approaches based on biotechnology. Cuad. Invest. Biol., 20: 545-548
Koehler A, Wahl E, Soeffker K (2002). Functional and morphological changes of lysosomes as prognostic biomarkers of toxic liver injury in a marine flatfish (Platichthys flesus L.). Environmental Toxicology and Chemistry, 21(11): 2434–2444
OiE (2003). Manual of diagnostic tests for aquatic animals. World Organisation for Animal Health.
http://www.oie.int/eng/normes/fmanual/A_index.htm. , assessed January 2009, 7 pp
Tiedemann A (2003). Windenergieparke im Meer - Perspektiven für den umweltverträglichen Einstieg in eine neue Großtechnologie. In: Lozán J, Rachor E, Reise K, Sündermann J, Westernhagen H v (eds). Warnsignale aus Nordsee & Wattenmeer: Eine aktuelle Umweltbilanz. Wissenschaftliche Auswertungen, Hamburg, 142–148
Walter U, Buck BH, Liebezeit G (2010). Larval occurrence and settlement in the German Bight – a trial to estimate potentials for Mytilus edulis culture in offshore areas. Aquaculture International (submitted)
Chapter 06
Chapter 06 Attachment properties of blue mussels 43