11.3.2 Bivalve Species
Following mainly biological and technical requirements, but also a regulatory and
economic framework, three filter-feeding bivalves were identified as potentially
successful candidates for offshore cultivation in the German Bight: Mytilus edulis,
Crassostrea gigas and Ostrea edulis (Buck et al. 2006a).
M. edulis and O. edulis are native species while C. gigas was introduced to
German waters in the 1960s due to aquaculture activities in the Netherlands
(Diederich et al. 2004; Smaal et al. 2009). By now C. gigas is distributed all over
the German North Sea coastline and is commercially cultured since the 1980s. All
three species are classified as extractive species in aquaculture and are therefore
ideal candidates for offshore cultivation with IMTA concepts. They reduce nutrient
emissions of higher trophic species by filter-feeding and require low maintenance as
they do not require additionally feed (Pogoda et al. 2011).
During several studies, these candidates have been cultivated at various offshore
sites and approved their suitability for offshore aquaculture operations in the future.
Results of these studies clearly elucidated that all three bivalve species grow successfully under exposed conditions in offshore environments (e.g. Buck 2007;
Brenner et al. 2012; Pogoda et al. 2011, 2013). As the “multi-use” of offshore wind
farms for aquaculture installations will facilitate the further expansion of environmentally friendly and sustainable aquaculture, most test sites of the described
cultivation experiments were conducted in North Sea areas of two offshore wind
farms (OWF): “Butendiek” (in operation since 2015) and “Nordergründe”
1
(currently under construction in late 2016, Fig. 11.6).
11.3.2.1 Candidate: Mytilus edulis
Biological conditions: Blue mussels cultivated in offshore areas of the German
North Sea, for the most part, show high growth rates compared to those grown in
nearshore sites (e.g. Buck 2004, 2007). This is due to the fact that water quality
(e.g. less urban sewage) and oxygen concentrations are more suitable and the
infestation of parasites is low or non-existent (Buck et al. 2005; Pogoda 2012).
However, in areas under estuarine influence and/or exposure to fluvial transport
point to a comparable probability for high contamination loads similar to nearshore
areas, thus potentially reducing fitness (Brenner et al. 2012). In Project No. 2 “Open
Ocean Aquaculture” mooring devices were deployed to test the feasibility of mussel
and seaweed aquaculture at offshore sites within areas of planned wind farms
(Fig. 11.7a). Larval abundance of mussels tended to decrease with increasing distance from shore (Walter et al. 2002; Buck 2017). However, several offshore sites
were identified, where larval concentration was sufficient enough to facilitate
adequate natural seeding (Buck 2007) (Fig. 11.7b). Alternatively, limited spat
1
Nordergründe is an area in the Weser estuary off the German Coast in the German Bight (Fig. 8).
266
B.H. Buck et al.
Following mainly biological and technical requirements, but also a regulatory and
economic framework, three filter-feeding bivalves were identified as potentially
successful candidates for offshore cultivation in the German Bight: Mytilus edulis,
Crassostrea gigas and Ostrea edulis (Buck et al. 2006a).
M. edulis and O. edulis are native species while C. gigas was introduced to
German waters in the 1960s due to aquaculture activities in the Netherlands
(Diederich et al. 2004; Smaal et al. 2009). By now C. gigas is distributed all over
the German North Sea coastline and is commercially cultured since the 1980s. All
three species are classified as extractive species in aquaculture and are therefore
ideal candidates for offshore cultivation with IMTA concepts. They reduce nutrient
emissions of higher trophic species by filter-feeding and require low maintenance as
they do not require additionally feed (Pogoda et al. 2011).
During several studies, these candidates have been cultivated at various offshore
sites and approved their suitability for offshore aquaculture operations in the future.
Results of these studies clearly elucidated that all three bivalve species grow successfully under exposed conditions in offshore environments (e.g. Buck 2007;
Brenner et al. 2012; Pogoda et al. 2011, 2013). As the “multi-use” of offshore wind
farms for aquaculture installations will facilitate the further expansion of environmentally friendly and sustainable aquaculture, most test sites of the described
cultivation experiments were conducted in North Sea areas of two offshore wind
farms (OWF): “Butendiek” (in operation since 2015) and “Nordergründe”
1
(currently under construction in late 2016, Fig. 11.6).
11.3.2.1 Candidate: Mytilus edulis
Biological conditions: Blue mussels cultivated in offshore areas of the German
North Sea, for the most part, show high growth rates compared to those grown in
nearshore sites (e.g. Buck 2004, 2007). This is due to the fact that water quality
(e.g. less urban sewage) and oxygen concentrations are more suitable and the
infestation of parasites is low or non-existent (Buck et al. 2005; Pogoda 2012).
However, in areas under estuarine influence and/or exposure to fluvial transport
point to a comparable probability for high contamination loads similar to nearshore
areas, thus potentially reducing fitness (Brenner et al. 2012). In Project No. 2 “Open
Ocean Aquaculture” mooring devices were deployed to test the feasibility of mussel
and seaweed aquaculture at offshore sites within areas of planned wind farms
(Fig. 11.7a). Larval abundance of mussels tended to decrease with increasing distance from shore (Walter et al. 2002; Buck 2017). However, several offshore sites
were identified, where larval concentration was sufficient enough to facilitate
adequate natural seeding (Buck 2007) (Fig. 11.7b). Alternatively, limited spat
1
Nordergründe is an area in the Weser estuary off the German Coast in the German Bight (Fig. 8).
266
B.H. Buck et al.