P. palmata requires a site with high water current for nutrient and CO 2 exchange
across the surface of the fronds as well as for prevention of fouling (Werner and
Dring 2011), thus making it a good candidate for offshore cultivation. Currents with
flow rates of minimum 5–10 cm s
−1 are needed for Palmaria cultivation. However,
the exposure of the site to wave action should be moderate (Werner and Dring
2011). Therefore, for offshore cultivation of dulse wave exposure and current
velocities need to be considered to reach optimal growth conditions and to reduce
loss of biomass.
Another limiting factor for growth of P. palmata in the wind farms of the
German Bight is the relatively high water temperatures in summer. Grote and Buck
(2017) found reduced SGRs of 2.2% d
−1 at 16.5 °C. Minimum winter temperatures
are not considered to be damaging unless there is the unlikely threat of
ice-formation which could cause abrasion of the cultures. Growth of P. palmata is
optimal at temperatures between 6° and 12 °C, but the red alga will grow well to
temperatures up to 15 °C (Morgan et al. 1980b; Morgan and Simpson 1981) or
17 °C (Grote and Buck 2017), with these differences probably resulting from different temperature ranges for different populations.
The size at which P. palmata should be harvested is a frond length of 30–40 cm
(Werner and Dring 2011). It is crucial to monitor the algae during spring and
especially during the summer months to ensure that the dulse is harvested before the
fronds are overgrown by fouling organisms (Werner and Dring 2011). This is very
important when P. palmata is grown for human consumption, which requires high
quality harvests. As growth is expected to be reduced during the summer months
due to higher temperatures in the German Bight, the optimal time for harvest would
be in June (Grote and Buck 2017). As the growth of P. palmata was enhanced in
the vicinity of fish farms at sea (Sanderson et al. 2012) and as it is an robust alga
thought to withstand strong forces, P. palmata is thought to be an ideal extractive
candidate for offshore IMTA (Grote and Buck 2017). However, the potential forces
experienced by the attached algae offshore need to be studied in more detail.
11.3.1.3 Candidate: Delesseria sanguinea
Sea beech is an European endemic, sublittoral red alga with a distribution range
from northern Spain and Portugal to northern Norway and Iceland (Lüning 1990). It
is thought to be a candidate for offshore aquaculture systems due to its biological
tolerance to environmental conditions (Lüning 1990); however, biological studies
on multi-use and offshore aquaculture success of this species are still missing. The
reproductive season of D. sanguinea lasts from October to February/April at
Helgoland (Molenaar and Breeman 1997) and the red alga can tolerate temperatures
between 13 and 23 °C, but temperatures for optimal growth lie between 10 and
15 °C (Lüning 1990). D. sanguinea is used in the cosmetics industry for its anticoagulant properties and vitamin K content; the active principle being termed
delesserine (Guiry and Blunden 1991).
11 The German Case Study: Pioneer Projects of Aquaculture …
265
across the surface of the fronds as well as for prevention of fouling (Werner and
Dring 2011), thus making it a good candidate for offshore cultivation. Currents with
flow rates of minimum 5–10 cm s
−1 are needed for Palmaria cultivation. However,
the exposure of the site to wave action should be moderate (Werner and Dring
2011). Therefore, for offshore cultivation of dulse wave exposure and current
velocities need to be considered to reach optimal growth conditions and to reduce
loss of biomass.
Another limiting factor for growth of P. palmata in the wind farms of the
German Bight is the relatively high water temperatures in summer. Grote and Buck
(2017) found reduced SGRs of 2.2% d
−1 at 16.5 °C. Minimum winter temperatures
are not considered to be damaging unless there is the unlikely threat of
ice-formation which could cause abrasion of the cultures. Growth of P. palmata is
optimal at temperatures between 6° and 12 °C, but the red alga will grow well to
temperatures up to 15 °C (Morgan et al. 1980b; Morgan and Simpson 1981) or
17 °C (Grote and Buck 2017), with these differences probably resulting from different temperature ranges for different populations.
The size at which P. palmata should be harvested is a frond length of 30–40 cm
(Werner and Dring 2011). It is crucial to monitor the algae during spring and
especially during the summer months to ensure that the dulse is harvested before the
fronds are overgrown by fouling organisms (Werner and Dring 2011). This is very
important when P. palmata is grown for human consumption, which requires high
quality harvests. As growth is expected to be reduced during the summer months
due to higher temperatures in the German Bight, the optimal time for harvest would
be in June (Grote and Buck 2017). As the growth of P. palmata was enhanced in
the vicinity of fish farms at sea (Sanderson et al. 2012) and as it is an robust alga
thought to withstand strong forces, P. palmata is thought to be an ideal extractive
candidate for offshore IMTA (Grote and Buck 2017). However, the potential forces
experienced by the attached algae offshore need to be studied in more detail.
11.3.1.3 Candidate: Delesseria sanguinea
Sea beech is an European endemic, sublittoral red alga with a distribution range
from northern Spain and Portugal to northern Norway and Iceland (Lüning 1990). It
is thought to be a candidate for offshore aquaculture systems due to its biological
tolerance to environmental conditions (Lüning 1990); however, biological studies
on multi-use and offshore aquaculture success of this species are still missing. The
reproductive season of D. sanguinea lasts from October to February/April at
Helgoland (Molenaar and Breeman 1997) and the red alga can tolerate temperatures
between 13 and 23 °C, but temperatures for optimal growth lie between 10 and
15 °C (Lüning 1990). D. sanguinea is used in the cosmetics industry for its anticoagulant properties and vitamin K content; the active principle being termed
delesserine (Guiry and Blunden 1991).
11 The German Case Study: Pioneer Projects of Aquaculture …
265