Biology Reference
In-Depth Information
aquaculture has now been focused on the cultivation of high-value seaweed species
which have not been previously used in integrated systems, and on improving tank-
culture success for seaweed yields and for reduction of undesirable effects of
intensive fish mariculture (e.g., Mata et al.
2006
; Hern
´
ndez et al.
2006
; Flower
and Neori
2008
).
The majority of the research on integrated mariculture is based on the integration
of biofiltering seaweed and fish aquaculture. There are also studies focussed on
the integration of seaweed and shrimp culture (e.g., Jones et al.
2001
; Sato et al.
2006a
,
b
; Lombardi et al.
2006
) and human sewage (Gordillo et al.
2002
). Thus,
treatment with macroalgae has now become an alternative to earlier adoptions of
microalgae, but care must be taken when extrapolating pilot plant results to a larger
scale. The factors for considering the advantages of using a given species over
others should include that they are abundant in the system during the whole year
and are easier to maintain in long-term cultures. For example, for human sewage
treatment Gordillo et al. (
2002
) showed that the intertidal species
Fucus vesiculosus
and
F. serratus
have the ability to adapt to high nutrient concentrations and low
salinity and are, therefore, suitable candidates for wastewater treatment, while the
subtidal
Laminaria digitata
would be a less suitable species since it did not stand
long periods under reduced salinity despite its N accumulating ability.
4.6.1 Nutrient Uptake at High Concentrations
Frequently, when a given resource is available at concentrations well above the
K
0.5
of the high affinity uptake mechanism, a second uptake mechanism can be observed
showing uptake rates above the
V
max
of the former (e.g., Fujita
1985
; Gordillo et al.
2002
, Fig.
4.2
). Nonsaturating and biphasic uptake kinetics have been observed in
coastal phytoplankton assemblages, which normally bloom under conditions of
high nutrient fluxes and turbulent mixing and are considered to be mechanisms of
adaptation to such environments (Collos et al.
1997
; Lomas and Glibert
1999
).
Furthermore, nonsaturating nutrient uptake kinetics have been reported for several
macroalgae species by Wallentinus (
1984
) and Fujita (
1985
). Biphasic kinetics was
observed in the red alga
Gracilaria gaditana
when inorganic carbon uptake was
investigated at high CO
2
levels (Andr´a et al.
1999
). Gordillo et al. (
2002
)
evidenced that the onset of a second mechanism in
Fucus serratus
dealing with
high external phosphate is apparently different from the high affinity one operating
at low concentrations (Fig.
4.2
). These adaptations would make the N:P ratio for
uptake drop from values around 30 at relatively subsaturating nutrient levels to
values more in accordance with internal inorganic N:P ratios observed when
internal pools are saturated. Since common assay concentrations are rarely above
30
M for both N and P, Lomas and Glibert (
1999
) have suggested, from their
results with phytoplankton, that more nonsaturating and biphasic uptake kinetics
may be found in algae of coastal areas if researchers use a wider range of
concentrations in their assays.
m
