BIOLOGY OF SEAWEEDS OF ECONOMIC IMPORTANCE
145
augmentation of the stocks from sporelings would have taken place.
The suggestion was also made that such favourable years may be long
spaced. Whilst younger plants are to be found at the top of the Ascophyllum zone, it is possible that these are in a state of protracted
juvenility-a condition noted by Knight and Parke (1950) for highlevel Fucus vesiculosus. There is the possibility that favourable periods
for sporeling growth and subsequent recruitment of young plants
might only occur over 10-15 year intervals. The competitive factor of
other fucoid algae on areas cleared of Ascophyllum has been noted
above. The time taken for re-establishment of the Ascophyllum coverthe climax in suitable habitats, is as yet unknown but will clearly take
many years. Indiscriminate and uncontrolled harvesting can therefore
present a major problem over the years, and certainly with Ascophyllum some measure of conservation would appear necessary, and
this applies to areas where the population seems less severely affected
by regular cropping, e.g. Galway, West Ireland (Baardseth, 1955b).
A detailed study of the free-living forms of Ascophyllum, particularly A . nodosum ecad mackai, was carried out by Gibb (1957). This
form arises entirely from broken pieces of the attached plant which
are carried into land-locked seas sheltered from wave-action, where
there are marked salinity variations due to fresh-water streams, and
where there is a flat substratum of sand or of thin mud overlying
pebbles or stones. These conditions are found in the sheltered sea
lochs on the coast of Scotland. Development of the ecad can be followed
through a number of stages, of which a marked increase of branching
is the first indication, first seen in the receptacles and then observed
on the main branches. Low salinities seem to govern this condition,
and midshore plants show a much greater degree of apical branching
than do those at higher levels. Marked increase in lateral branching
follows alternate periods of immersion in fresh and salt water. Frond
injury will also stimulate lateral branch formation in the ecad. Continued growth in water of low salinity results in a thinner, more flexible
frond. Bending and twisting of the frond also occurs-a condition
commonly observed in salt-marsh fucoids. The habit of vesicle formation may also be lost under these conditions, and prolific receptacle
formation observed. The release of gametes commences in April and
continues over a more protracted period than that observed with the
attached plants, but oospores develop into the attached form of plant.
In general the standing crop is maintained by vegetative growth of
the ecad, although certain diseased conditions appear to have caused
appreciable reductions (e.g. " mud " decay; " freshwater " decay;
" spotted " decay; " sun )' decay). " Beach " forms and " turf "
145
augmentation of the stocks from sporelings would have taken place.
The suggestion was also made that such favourable years may be long
spaced. Whilst younger plants are to be found at the top of the Ascophyllum zone, it is possible that these are in a state of protracted
juvenility-a condition noted by Knight and Parke (1950) for highlevel Fucus vesiculosus. There is the possibility that favourable periods
for sporeling growth and subsequent recruitment of young plants
might only occur over 10-15 year intervals. The competitive factor of
other fucoid algae on areas cleared of Ascophyllum has been noted
above. The time taken for re-establishment of the Ascophyllum coverthe climax in suitable habitats, is as yet unknown but will clearly take
many years. Indiscriminate and uncontrolled harvesting can therefore
present a major problem over the years, and certainly with Ascophyllum some measure of conservation would appear necessary, and
this applies to areas where the population seems less severely affected
by regular cropping, e.g. Galway, West Ireland (Baardseth, 1955b).
A detailed study of the free-living forms of Ascophyllum, particularly A . nodosum ecad mackai, was carried out by Gibb (1957). This
form arises entirely from broken pieces of the attached plant which
are carried into land-locked seas sheltered from wave-action, where
there are marked salinity variations due to fresh-water streams, and
where there is a flat substratum of sand or of thin mud overlying
pebbles or stones. These conditions are found in the sheltered sea
lochs on the coast of Scotland. Development of the ecad can be followed
through a number of stages, of which a marked increase of branching
is the first indication, first seen in the receptacles and then observed
on the main branches. Low salinities seem to govern this condition,
and midshore plants show a much greater degree of apical branching
than do those at higher levels. Marked increase in lateral branching
follows alternate periods of immersion in fresh and salt water. Frond
injury will also stimulate lateral branch formation in the ecad. Continued growth in water of low salinity results in a thinner, more flexible
frond. Bending and twisting of the frond also occurs-a condition
commonly observed in salt-marsh fucoids. The habit of vesicle formation may also be lost under these conditions, and prolific receptacle
formation observed. The release of gametes commences in April and
continues over a more protracted period than that observed with the
attached plants, but oospores develop into the attached form of plant.
In general the standing crop is maintained by vegetative growth of
the ecad, although certain diseased conditions appear to have caused
appreciable reductions (e.g. " mud " decay; " freshwater " decay;
" spotted " decay; " sun )' decay). " Beach " forms and " turf "