BIOLOGY 6P SEAWEEDS 0%’ BCON6MfO IMPORTANCE
197
falls off through the autumn. The formation and release of spermatia
follows a similar pattern. Plants bearing cystocarps increase in number
during the spring, but peak production is reached during the autumn.
Mini0 (1949) stated that in the lagoon of Venice the formation of cystocarps on Gracilaria followed a period of intensive vegetative growth,
and that their formation was stimulated by the diseased condition of
the fronds.
Some factors influencing the growth of Gracilaria plants were
studied by Causey et al. (1946) and Jones (1959b). Growth was
better in flowing water, and, whilst early growth was stimulated by
high levels of illumination, the slower growth subsequently observed
was due to bleaching effects through loss of the red pigment phycoerythrin. Under shaded conditions the red pigment was seen to return.
Gracilaria sporelings were found to be susceptible to intensive illumination, a feature frequently observed with sporelings of red algae (Boney
and Corner, 1962, 1963). Coalescence of young sporelings has been
observed under experimental conditions (Jones, 1956), and this was
observed to bring about an early stimulus of erect frond production
when compared with isolated sporelings. With large “rafts” of
coalesced sporelings erect fronds were obtained evenly spaced over the
encrusting growths, and this phenomenon has been observed with
sporelings from carpospores and tetraspores. Similar types of growth
have been observed under field conditions, and these would have clear
advantages where an unstable substratum such as sand may on
occasions cover the young plant.
Studies on spore emission and attachment have been reported by
Segawa et al. (1955a,b) and Sawada (1956). Spore emission appears to
be influenced by osmotic changes in the surrounding medium, and is
initiated by changes in the inner pressure of the spore material. The
degree of drying undergone by the frond also appears to be important,
since dried fronds release their spores more rapidly than those which
remain immersed. A large-scale emission of spores from cystocarps on
the same plant is sometimes observed, and this could result in dense
settlements on restricted areas of the shore, and this would encourage
the spore coalescence reported above.
Gracilaria plants are cultivated in Tokyo Bay by suspending
branches of the plant in twists of rope in waters rich in nutrients.
Growth of the attached plants is also encouraged by supplying suitable
substrata, e.g. shells, small stones etc. (Scagel, 1961). I n Tokyo Bay
the plant is harvested mainly in September and October. The data
from other localities suggest that the summer is the best time to collect
the plants.
197
falls off through the autumn. The formation and release of spermatia
follows a similar pattern. Plants bearing cystocarps increase in number
during the spring, but peak production is reached during the autumn.
Mini0 (1949) stated that in the lagoon of Venice the formation of cystocarps on Gracilaria followed a period of intensive vegetative growth,
and that their formation was stimulated by the diseased condition of
the fronds.
Some factors influencing the growth of Gracilaria plants were
studied by Causey et al. (1946) and Jones (1959b). Growth was
better in flowing water, and, whilst early growth was stimulated by
high levels of illumination, the slower growth subsequently observed
was due to bleaching effects through loss of the red pigment phycoerythrin. Under shaded conditions the red pigment was seen to return.
Gracilaria sporelings were found to be susceptible to intensive illumination, a feature frequently observed with sporelings of red algae (Boney
and Corner, 1962, 1963). Coalescence of young sporelings has been
observed under experimental conditions (Jones, 1956), and this was
observed to bring about an early stimulus of erect frond production
when compared with isolated sporelings. With large “rafts” of
coalesced sporelings erect fronds were obtained evenly spaced over the
encrusting growths, and this phenomenon has been observed with
sporelings from carpospores and tetraspores. Similar types of growth
have been observed under field conditions, and these would have clear
advantages where an unstable substratum such as sand may on
occasions cover the young plant.
Studies on spore emission and attachment have been reported by
Segawa et al. (1955a,b) and Sawada (1956). Spore emission appears to
be influenced by osmotic changes in the surrounding medium, and is
initiated by changes in the inner pressure of the spore material. The
degree of drying undergone by the frond also appears to be important,
since dried fronds release their spores more rapidly than those which
remain immersed. A large-scale emission of spores from cystocarps on
the same plant is sometimes observed, and this could result in dense
settlements on restricted areas of the shore, and this would encourage
the spore coalescence reported above.
Gracilaria plants are cultivated in Tokyo Bay by suspending
branches of the plant in twists of rope in waters rich in nutrients.
Growth of the attached plants is also encouraged by supplying suitable
substrata, e.g. shells, small stones etc. (Scagel, 1961). I n Tokyo Bay
the plant is harvested mainly in September and October. The data
from other localities suggest that the summer is the best time to collect
the plants.