1 in summer, which indicate well-fed animals and excellent growing conditions at
offshore cultivation sites in the German Bight (Pogoda et al. 2013).
Also the amount of essential fatty acids greatly affects growth and condition of
oysters (Pazos et al. 1996). The fatty acid compositions of the European and the
Pacific oysters were dominated by 16:0, 20:5(n − 3) and 22:6(n − 3), major
components of phospholipids of typical marine organisms. Both species of
offshore-cultivated oysters showed the accumulation of lipids as energy reserves
during high food availability from spring to early summer. Diatom markers
increased during spring and early summer in both oyster species and suggest a diet
rich in diatoms (Pogoda et al. 2013). Increasingly high ratios of (n − 3)/(n − 6)
during the cultivation experiment underline the excellent physiological condition of
both offshore-cultivated oyster species (Pogoda et al. 2013; Pazos et al. 1996).
The combination of successful growth performance and obviously excellent
overall condition of offshore-cultivated oysters resulted in insignificant mortalities.
In contrast to commercial oyster production in nearshore environments, which often
suffer from high mortalities, offshore survival rates for both oyster species were
high (>96% in 2004, >99% in 2007) and encourage open ocean cultivation (Pogoda
et al. 2011).
Parasite infestation: Studies on the macroparasite burden of offshore-cultivated
European and Pacific oysters and Blue mussels reported a zero infestation at offshore locations in the North Sea (Fig. 11.16a–c). In general, parasites can affect
condition and health of host animals. Buck et al. (2005), Brenner (2009) and
Pogoda et al. (2012) have shown that offshore grown mussels and oysters were free
of macroparasites and that infestation rates increased with proximity of the sites to
shore, respectively; intertidal mussels and oysters showed the highest numbers of
parasites. The debate over the effects of parasites on the energy status and overall
health of the host is still open as robust data to elucidate these issues is still lacking.
Three major groups of macroparasites are known to infest North Sea mussels and
oysters: shell-boring polychaetes, trematodes and mytilicolid copepods. Absence of
trematodes at offshore locations can be explained by their complex life cycle: they
often infest intertidal gastropods as first intermediate hosts (e.g. Littorina littorea
and Hydrobia ulva). These are typical macroparasites of inshore bivalves, which,
however, are completely absent in offshore cultivated oysters and mussels.
Due to the absence of these exclusively coastal organisms the parasite’s life
cycle cannot be completed in offshore regions (Buck et al. 2005). Mytilicolid
copepods and shell-boring polychaetes (e.g. Polydora ciliata) are abundant in
inshore waters (Thieltges et al. 2006). However, their short planktonic larval phase
restricts successful dispersion to coastal waters. Larvae drifting away from the coast
are bound to die due to predation or starvation in the absence of hosts, which are
only available at very few selected offshore culture locations (Buck et al. 2005).
These results present a commercial advantage of such offshore shellfish cultures.
All known micro- and macroparasites found in European coastal waters are
harmless to consumers, but may have negative condition effects (macroparasites)
and cause higher mortalities (microparasites) in infested hosts (Brenner et al. 2012).
11 The German Case Study: Pioneer Projects of Aquaculture …
277
offshore cultivation sites in the German Bight (Pogoda et al. 2013).
Also the amount of essential fatty acids greatly affects growth and condition of
oysters (Pazos et al. 1996). The fatty acid compositions of the European and the
Pacific oysters were dominated by 16:0, 20:5(n − 3) and 22:6(n − 3), major
components of phospholipids of typical marine organisms. Both species of
offshore-cultivated oysters showed the accumulation of lipids as energy reserves
during high food availability from spring to early summer. Diatom markers
increased during spring and early summer in both oyster species and suggest a diet
rich in diatoms (Pogoda et al. 2013). Increasingly high ratios of (n − 3)/(n − 6)
during the cultivation experiment underline the excellent physiological condition of
both offshore-cultivated oyster species (Pogoda et al. 2013; Pazos et al. 1996).
The combination of successful growth performance and obviously excellent
overall condition of offshore-cultivated oysters resulted in insignificant mortalities.
In contrast to commercial oyster production in nearshore environments, which often
suffer from high mortalities, offshore survival rates for both oyster species were
high (>96% in 2004, >99% in 2007) and encourage open ocean cultivation (Pogoda
et al. 2011).
Parasite infestation: Studies on the macroparasite burden of offshore-cultivated
European and Pacific oysters and Blue mussels reported a zero infestation at offshore locations in the North Sea (Fig. 11.16a–c). In general, parasites can affect
condition and health of host animals. Buck et al. (2005), Brenner (2009) and
Pogoda et al. (2012) have shown that offshore grown mussels and oysters were free
of macroparasites and that infestation rates increased with proximity of the sites to
shore, respectively; intertidal mussels and oysters showed the highest numbers of
parasites. The debate over the effects of parasites on the energy status and overall
health of the host is still open as robust data to elucidate these issues is still lacking.
Three major groups of macroparasites are known to infest North Sea mussels and
oysters: shell-boring polychaetes, trematodes and mytilicolid copepods. Absence of
trematodes at offshore locations can be explained by their complex life cycle: they
often infest intertidal gastropods as first intermediate hosts (e.g. Littorina littorea
and Hydrobia ulva). These are typical macroparasites of inshore bivalves, which,
however, are completely absent in offshore cultivated oysters and mussels.
Due to the absence of these exclusively coastal organisms the parasite’s life
cycle cannot be completed in offshore regions (Buck et al. 2005). Mytilicolid
copepods and shell-boring polychaetes (e.g. Polydora ciliata) are abundant in
inshore waters (Thieltges et al. 2006). However, their short planktonic larval phase
restricts successful dispersion to coastal waters. Larvae drifting away from the coast
are bound to die due to predation or starvation in the absence of hosts, which are
only available at very few selected offshore culture locations (Buck et al. 2005).
These results present a commercial advantage of such offshore shellfish cultures.
All known micro- and macroparasites found in European coastal waters are
harmless to consumers, but may have negative condition effects (macroparasites)
and cause higher mortalities (microparasites) in infested hosts (Brenner et al. 2012).
11 The German Case Study: Pioneer Projects of Aquaculture …
277