124
J.E. Merrill
An important advantage of Gracilaria for use in water quality improvement is its ability to tolerate a wide range of salinities and relatively low water
motion; conditions that would be considered unfavorable for other species,
but which are fairly common in coastal areas subject to damaging green tides.
Many species of Gracilaria are also tolerant of relatively high temperatures
(up to 30°C) and of wide temperature ranges. There are species of Gracilaria
native to most of the world's coastlines and it is highly likely that strains with
adequate commercial characteristics can be found in a given area.
4.3.4 Additional Alternatives
While the examples cited above represent cases of complete cultivation,
there may be circumstances in which controlled cultivation is uneconomical, or is undesirable for other reasons. In such cases, it may be possible to
apply simplified techniques toward "enhancement" of desired species. For
example, in some shallow lagoons where unattached populations of Ulva
dominate, the simple addition of shell fragments or pebbles, with or
without pre-inoculation with spores, may be sufficient to stimulate a shift to
populations of Gracilaria or Gracilariopsis in that these species seem to
prefer at least some attachment point.
4.4 Nutrient Removal
Ryther (1983) has calculated that a one-hectare Gracilaria farm is capable
of removing all of the nitrogen and much of the phosphorus from 350 m 3 of
wastewater per day, equivalent to the output of 1000 people. The nutrient
loading of fish cultivation and processing wastes have been effectively
reduced by natural or cultivated macro algal populations (Markovtsev and
Krupnova 1988; Subandar et al. 1993).
A useful framework within which to consider the beneficial value of
nutrient uptake and removal is that of Algal Biomass Potential (ABP;
Oswald 1988). In the presence of sufficient quantities of other elements, a
single nutrient may support a finite quantity of biomass production by a
given species. For example, ABP can be defined for nitrogen as follows:
ABP ( I
d -3) available N (mg dm -3)
a gae mg m
= algal N content (%) .
(1)
If we consider a system supporting growth of Ulva containing approximately 3.5% N with a nitrogen flux of 20 mg dm -\ we can calculate the
J.E. Merrill
An important advantage of Gracilaria for use in water quality improvement is its ability to tolerate a wide range of salinities and relatively low water
motion; conditions that would be considered unfavorable for other species,
but which are fairly common in coastal areas subject to damaging green tides.
Many species of Gracilaria are also tolerant of relatively high temperatures
(up to 30°C) and of wide temperature ranges. There are species of Gracilaria
native to most of the world's coastlines and it is highly likely that strains with
adequate commercial characteristics can be found in a given area.
4.3.4 Additional Alternatives
While the examples cited above represent cases of complete cultivation,
there may be circumstances in which controlled cultivation is uneconomical, or is undesirable for other reasons. In such cases, it may be possible to
apply simplified techniques toward "enhancement" of desired species. For
example, in some shallow lagoons where unattached populations of Ulva
dominate, the simple addition of shell fragments or pebbles, with or
without pre-inoculation with spores, may be sufficient to stimulate a shift to
populations of Gracilaria or Gracilariopsis in that these species seem to
prefer at least some attachment point.
4.4 Nutrient Removal
Ryther (1983) has calculated that a one-hectare Gracilaria farm is capable
of removing all of the nitrogen and much of the phosphorus from 350 m 3 of
wastewater per day, equivalent to the output of 1000 people. The nutrient
loading of fish cultivation and processing wastes have been effectively
reduced by natural or cultivated macro algal populations (Markovtsev and
Krupnova 1988; Subandar et al. 1993).
A useful framework within which to consider the beneficial value of
nutrient uptake and removal is that of Algal Biomass Potential (ABP;
Oswald 1988). In the presence of sufficient quantities of other elements, a
single nutrient may support a finite quantity of biomass production by a
given species. For example, ABP can be defined for nitrogen as follows:
ABP ( I
d -3) available N (mg dm -3)
a gae mg m
= algal N content (%) .
(1)
If we consider a system supporting growth of Ulva containing approximately 3.5% N with a nitrogen flux of 20 mg dm -\ we can calculate the