Biology Reference
In-Depth Information
and lifting of these lines into a horizontal position overcomes first overexposure,
then shading problems in growing sporophytes, while reducing effects of cross
currents and storms on only horizontally attached lines (
FAO 2005-2011b
). From
the various methods (e.g., Holt and Kain
1983
; Kawashima
1984
; Kain and Dawes
1987
; Dawes
1988
; Kain
1991
; Merrill and Gillingham
1991
; Critchley and Ohno
1997
; Buck and Buchholz
2004
), the locally appropriate one has to be chosen for
the special conditions of a given farming site.
Longline systems installed in harsh offshore conditions, to where farms could be
expanded, were not robust enough as there is a considerable stress on support
material and algae (Buck
2004
; Buck and Buchholz
2004
). Among the various
suggestions for technical structures that have been made (Polk
1996
; Hesley
1997
;
Stickney
1998
; Bridger and Costa-Pierce
2003
) a ring design did withstand strong
currents and wind waves and is still the most promising (Buck and Buchholz
2004
).
The idea of utilizing the grounding structures of offshore wind generators for the
fixation of aquaculture systems is intriguing (e.g., Buck
2002
; Krause et al.
2003
;
Buck et al.
2004
) and the first experiments on
Laminaria
species show that adapted
to strong currents as young individuals, they grow well at exposed sites (Buck and
Buchholz
2005
).
The cultivation of seaweeds at sea or in ponds flushed by incoming seawater has
lately been supplemented or completely exchanged for land-based tank cultivation
for smaller rhodophytes and chlorophytes (see Sect.
22.1.3.2
) as well as large kelps.
L
uning and Pang (
2003
) kept free floating sporophytes of laminarians or
Palmaria
palmata
circulating in the water agitated by air. The tanks allowed a high cultiva-
tion density of 10 kg m
2
, since shading was amended by the continuous turnover
of fronds toward the light. Uniform exposure to nutrients was likewise facilitated
and the infestation with epiphytes was kept very low (Ryther et al
.
1979
; Bidwell
et al.
1985
). The L
€
uning and Pang (
2003
) system was additionally supported by a
continuous short day treatment. The same short day treatment (8 h light) using
outdoor tanks with automatic blinds resulted in prolonged growth activity of
Laminaria digitata
that also seemed to deter epiphyte settlement (G´mez and
Luning
2001
). The experience gained in tank cultivation is a valuable basis for
some of the internationally developing integrated mariculture systems (see citations
in Neori et al.
2004
, p. 376; Abreu et al.
2011
; Pereira et al.
2011
).
The world population recently reached the seven billion mark and a sustained or
rather growing supply of protein from aquatic animals is highly desirable. Concom-
itantly there is an increasing concern about the negative consequences of intensive
and constantly spreading aquaculture of fish, shrimps, and mollusks. Therefore, the
remediation of negative consequences has been a field of intensive research during
the last decade. Two ecologically sensible strategies to meet the requirements for
more space allotted to aquaculture have been and will continue to be tested: One is
the offshore aquaculture that to date seems very expensive and technically demand-
ing, but will allow considerable mass production. The other is the very promising
but likewise complicated Integrated Multi-Trophic Aquaculture (IMTA) approach.
€