| Summary: | Porphyra yezoensis has been cultivated for centuries in Asia. Ocean-based
operations, where the blade phase is grown attached to synthetic nets, and placed in
the ocean for grow-out, are the norm. There are many problems associated with this
type of cultivation, many of which could potentially be overcome by using land-based
tanks for grow-out of blades. However before land-based mariculture can begin,
research is needed into techniques for the production of blade suspension cultures, as
well as into the nutritional requirements of free-floating blades. This thesis reports on
experiments investigating these areas of research, and represents a step towards land-based
cultivation.
Techniques for propagating Porphyra yezoensis (strain U-51) blades using both
conchospores and monospores in laboratory scale land-based tank culture were
investigated. Suspension cultures of P. yezoensis blades were produced by seeding
conchospores onto various fixed and suspended substrata. The use of CaCO3
suspended substrata (particle size 74-212 µm) resulted in the highest early growth
rates (10% per day) because of their rough surface topography, which was ideal for
conchospore settlement. Suspended blades were significantly more lanceolate than
fixed blades, as they increased their L:W in response to higher water velocities. When
detached, the more ovoid fixed blades grew more slowly (4% per day) than the more
lanceolate suspended blades (13% per day) because their shape was not initially
adapted to the higher water velocities in suspension. By remaining in suspension,
blades were exposed equally to light and nutrients when suspended substrata were
used. Cheap sources of CaCO3 could be exploited (ground bivalve shells), and
suspended substrate techniques are not as labour intensive as fixed substrate methods
may be, reducing production costs.
Once blade suspension cultures were produced from conchospores, a
vegetative method for the propagation of blades via monospores was investigated.
Blades of various sizes were cut into tissue sections of various diameters. These tissue
sections were cultured under 15°C, 8L:16D photoperiod, 200 µmol photons m-2s-1, and
moderate aeration in 200 ml of f/2 medium. After an initial period of growth (10 days),
the tissue sections began to disintegrate as they released monospores. The best early
growth of new blades resulted with large tissue sections (93.8 mm²) from small blades
(5 - 7 cm in length), but all sections from all blade sizes tested released monospores,
and new suspension cultures resulted. This technique represents an easy, low-techology
method for blade propagation that has great potential for application on a
commercial scale. It allows the conchocelis to be by-passed during cultivation, and
allows the propagation of desirable clones.
The effect of tissue N and P on growth of Porphyra yezoensis (strain U-51)
blades in suspension cultures was investigated. Before these experiments began,
culture conditions such as photoperiod, temperature, and stocking density had to be
investigated so that they would be optimal for growth during experiments. Blades grew
best at 15°C, and 1.0 g fresh wt per 3L of medium. A range of photoperiods between 8
-12 h of light per day had no effect on growth. Because blades are typically grown
commercially during temperate winters, a photoperiod of 8L:16D was used.
Blades had the ability to store N in excess of requirements. The critical (0.40%
fresh wt) and subsistence (0.15% fresh wt) levels were constant regardless of N source
(NO3- or NH4+) or light level. Blades did not have the ability to store excess P, within the
range of P concentrations tested here. The subsistence quota for P was higher when
blades were grown on NH4+, suggesting a decreased ability to utilize tissue P for
growth. Therefore, N03- was considered a better N source than NH4+. Blades became
bright green in colour when they were N-limited, suggesting a link between
phycoerythrin and tissue N. The optimal molar N:P of 13-15 was constant regardless
of N source (NO3- or NH4+) or light level. N:P < 13 -15 indicated N limitation, while N:P >
13-15 indicated P limitation. P-limited and light-limited blades could store more N
when NH4+ was given, than when NO3- was the N source, suggesting physiological
mechanisms for taking advantage of this usually ephemeral N source, even when
growth was limited. N and P reserves were used up relatively quickly (5 days), a
characteristic of opportunistic species. Tissue analysis of N and P was shown to be a
very useful technique in determining nutrient status of P. yezoensis blades in land-based
tanks. As long as tissue N > 0.40% fresh wt and molar N:P = 13 -15, blades
grew unlimited by N or P. [Scientific formulae used in this abstract could not be reproduced.]
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