Biology Reference
In-Depth Information
of the suspension facilitate even settlement on collecting nets. After germination,
grow-out of the thalli takes place in relatively shallow bays, nets fixed, semi-
floating, or floating (Sahoo and Yarish
2005
; Pereira and Yarish
2010
). Fixed or
semi-floating, the alternation of immersion and desiccation with the tide is
guaranteed helping to avoid diseases caused by fungi or bacteria, reducing
epiphytic diatoms and improving the taste. Floating nets can be kept over slightly
deeper water (10-20 m), thereby extending the farming area. However, a nursery
system must be included that periodically dries the nets and hardens them (Pereira
and Yarish
2008
,
2010
). It is also possible and even improves the quality of the final
product to carefully freeze the nets with young thalli and store them at
20
C for
later grow-out (
FAO 2005-2011a
). Depending on the species it takes 40-50 days at
sea, for
P. haitanensis
and
P. yezoensis
, respectively, before the first crop can be
attained. Six to eight harvests are possible during 5 months of cultivation (Pereira
and Yarish
2010
).
The species with the highest production is the brown alga
Saccharina japonica
(formerly
Laminaria japonica
), “kombu.” 4.9 million tons of kombu were produced
in 2009, 84% of it grown in China, where the species is not endemic, but was
introduced in 1927 (Tseng
1987
; Lowther
2006
). Conventional “2 year cultivation”
of
S. japonica
took a period of 18 months at sea with at least another 2 months for
“seeding,” which resulted in relatively high prices for the product (Ohno
1993
).
“Cultivation by transplanting” uses natural
Saccharina
sporophytes either washed
ashore or manually thinned out. As the activity of the meristem increases in late
winter to early spring, new haptera are easily formed and allow a new attachment on
ropes during this time. Time from transplantation to harvest lasts 12-18 months
(Ohno
1993
). Only 12 months are needed for the widely applied so-called forced-
cultivation technique (Hasegawa
1971
; Ohno
1993
; Critchley and Ohno
1997
;
Sahoo and Yarish
2005
). This became possible due to scientific control of the entire
biphasic life cycle, where indoor facilities are necessary to manage the labor and
cost-intensive “seedling phase” (Tseng
1989
; Mc Hugh
2003
; Chen
2006
). A large
independence of naturally available seedstock could be attained by detaching
Laminaria
frond fractions from the meristem (Buchholz and Luning
1999
; see
also Luning et al.
2000
; Pang and Luning
2004
). Meiospores are artificially released
from sporogenous thalli, germinate to microscopic gametophytes, form zygotes, and
eventually produce young sporophytes that stick to ropes. In “the grow-out phase”
(Tseng
1989
), culture ropes with juvenile sporophytes are transferred to the open sea
where they grow to a frond length of approx. 1-2.5 m, depending on the species. If
the predicted shift of biogeographic areas becomes true (see also Chap.
18
by
Bartsch et al.), aquaculture of
S. japonica,
as an example, may be strongly impaired
in that the space and the period for grow-out in coastal waters are reduced. Young
seedlings do not tolerate more than 20
C and fronds have to be harvested at
21
C,
because they start to rot at higher temperatures (
FAO 2005-2011b
).
The most common design for grow-out of Laminariales in the open water is a
longline system of horizontal ropes parallel to the sea surface with anchoring
weights to stabilize the entire system and with buoys to provide flotation. Combin-
ing vertical arrangement of seeded culture lines as the first step and later suspension