BIOLOQY O F SEAWEEDS O F ECONOMIC IMPORTANCE
209
maxima were earlier in the year and that of Ascophyllum nodosum
showed little annual variation. In regions of low salinity, however, the
biotin content of the thalli was higher, and younger tissues had a
higher content than older fronds. The niacin and biotin contents of
thalli of Alaria esculenta followed much the same course over the year,
with maxima recorded in December, and the lowest values in June
when frond size is at a maximum. The suggestion has been made that
harvesting of Laminaria angustata should be restricted to third year
plants, so permitting growth, spore production and gametophyte
formation in the first two years (p. 160). It would hardly be practicable
to pick out the older plants from dense populations, so that harvesting
will normally include plants of all ages. The time of cutting could then
depend on the type of extractive required, and the extent to which this
fitted in with other aspects of the seasonal life, e.g. fruiting. For the
Laminaria plants analysed from European shores, the alginic acid
contents would appear to be highest in the earlier months of the year,
and mannitol and laminarin values are at a higher level later on. Stipe
variations over the seasons are of a much lower order than those of the
fronds, and similar observations were obtained when plants from
different depths were considered. Analysis of Laminaria plants from
Japan did not show the large-scale fluctuations in alginic acid content.
Nor did the Macrocystis plants analysed show any wide variations in
alginic acid content over the seasons. With the fucoid algae a similar
overall cycle of relative abundance of the main extractives was observed,
the one exception being Ascophyllum in that the alginic acid remained
at much the same level throughout the year. The effect of depletion
of reserves in formation of the fruiting receptacles of the fucoid algae
is a feature of their seasonal biology of marked significance for
harvesting.
C . Red algae
Studies on the seasonal change in the organic extractives of red
algae have shown that differences in gel strength are to be found, as
well as quantitative variations. The data, however, are less readily
available for the members of this class than for the brown algae.
Earlier observations have shown that in Chondrus there is a seasonal
variation in carbohydrate content, ranging from an early spring minimum to high values through summer and autumn (Butler, 1936).
Young and Langville (1968) found that the total ash content of Chondrus
was high in winter, falling to minimum values in summer, a result of the
observed. spring growth. For Qigartina stellata changes in the gel
strength of the extracts with the seasons have been observed (Marshall
209
maxima were earlier in the year and that of Ascophyllum nodosum
showed little annual variation. In regions of low salinity, however, the
biotin content of the thalli was higher, and younger tissues had a
higher content than older fronds. The niacin and biotin contents of
thalli of Alaria esculenta followed much the same course over the year,
with maxima recorded in December, and the lowest values in June
when frond size is at a maximum. The suggestion has been made that
harvesting of Laminaria angustata should be restricted to third year
plants, so permitting growth, spore production and gametophyte
formation in the first two years (p. 160). It would hardly be practicable
to pick out the older plants from dense populations, so that harvesting
will normally include plants of all ages. The time of cutting could then
depend on the type of extractive required, and the extent to which this
fitted in with other aspects of the seasonal life, e.g. fruiting. For the
Laminaria plants analysed from European shores, the alginic acid
contents would appear to be highest in the earlier months of the year,
and mannitol and laminarin values are at a higher level later on. Stipe
variations over the seasons are of a much lower order than those of the
fronds, and similar observations were obtained when plants from
different depths were considered. Analysis of Laminaria plants from
Japan did not show the large-scale fluctuations in alginic acid content.
Nor did the Macrocystis plants analysed show any wide variations in
alginic acid content over the seasons. With the fucoid algae a similar
overall cycle of relative abundance of the main extractives was observed,
the one exception being Ascophyllum in that the alginic acid remained
at much the same level throughout the year. The effect of depletion
of reserves in formation of the fruiting receptacles of the fucoid algae
is a feature of their seasonal biology of marked significance for
harvesting.
C . Red algae
Studies on the seasonal change in the organic extractives of red
algae have shown that differences in gel strength are to be found, as
well as quantitative variations. The data, however, are less readily
available for the members of this class than for the brown algae.
Earlier observations have shown that in Chondrus there is a seasonal
variation in carbohydrate content, ranging from an early spring minimum to high values through summer and autumn (Butler, 1936).
Young and Langville (1968) found that the total ash content of Chondrus
was high in winter, falling to minimum values in summer, a result of the
observed. spring growth. For Qigartina stellata changes in the gel
strength of the extracts with the seasons have been observed (Marshall