BIOLOGY OF SEAWEEDS OF ECONOMIC IMPORTANCE
151
establish. Gametophytes will normally grow under very shaded
conditions, and this is indicated in the very low light requirements
recorded above. Growth of the basal sporophylls is thought to be
partially dependent on translocation of nutrients from the surface
frondage. Neushul estimated that the minimum time for completion
of the sexual cycle in the sea would be 14 months, of which growth and
maturation of the sporophyte would take the most protracted time.
Growth of the gametophytes appears not to have been fully observed in
nature. Cribb (1954) failed to obtain gametophytes on plates of glass
and bakelite immersed in the sea near fruiting plants in Tasmanian
seas.
There is evidence that considerable damage is done to the kelp
frondage by browsing animals. North (1958) described how, after oil
pollution had killed most of the fauna, the sporophyte population
increased nearly tenthousandfold. Haxo and Neushul ( 1958) described
the grazing effects of “ kelp-fish ” and North (1964) commented on the
importance of sea urchins as kelp grazers, together with the gammarid
Amphithoe humeralis (Stimpson) and ldothea resecata (Stimpson).
Sporophytes transplanted from another locality appeared to suffer
more from animal depredation than the local population. Macrocystis
growth near sewage outfalls was found to be considerably less than
elsewhere, and this was found to be due to water turbidity not enabling
the growth of the kelps to keep pace with the browsing action of attendant herbivores. Suggestions have been made that transplants of
Macrocystis to Scottish shores might be attempted. North’s experiments
show that this type of work is attended by numerous difficulties. Thus
North (1964) observed that strains of Macrocystis from South California
were sensitive to sea temperatures a little more than 20°C for several
weeks, whilst plants from 600 km farther south were able to survive
exposure to 24°C.
Whilst the gametophyte phase poses many questions of ecological
interest, the great productivity of the surface frondage of the sporophyte is evidently well able to cope with regular harvesting.
8. Laminaria
The Laminaria sporophytes are macroscopic structures harvested
either for their food value, or for the extractives they contain. These
large plants alternate in their life history with microscopic filamentous
gametophytes from which the young sporophytes develop after fertilization of the oosphere within the oogonium. Hence a knowledge of
the growth and survival of the gametophytes is an essential preliminary
to studies on the seasonal life of the larger plants.
151
establish. Gametophytes will normally grow under very shaded
conditions, and this is indicated in the very low light requirements
recorded above. Growth of the basal sporophylls is thought to be
partially dependent on translocation of nutrients from the surface
frondage. Neushul estimated that the minimum time for completion
of the sexual cycle in the sea would be 14 months, of which growth and
maturation of the sporophyte would take the most protracted time.
Growth of the gametophytes appears not to have been fully observed in
nature. Cribb (1954) failed to obtain gametophytes on plates of glass
and bakelite immersed in the sea near fruiting plants in Tasmanian
seas.
There is evidence that considerable damage is done to the kelp
frondage by browsing animals. North (1958) described how, after oil
pollution had killed most of the fauna, the sporophyte population
increased nearly tenthousandfold. Haxo and Neushul ( 1958) described
the grazing effects of “ kelp-fish ” and North (1964) commented on the
importance of sea urchins as kelp grazers, together with the gammarid
Amphithoe humeralis (Stimpson) and ldothea resecata (Stimpson).
Sporophytes transplanted from another locality appeared to suffer
more from animal depredation than the local population. Macrocystis
growth near sewage outfalls was found to be considerably less than
elsewhere, and this was found to be due to water turbidity not enabling
the growth of the kelps to keep pace with the browsing action of attendant herbivores. Suggestions have been made that transplants of
Macrocystis to Scottish shores might be attempted. North’s experiments
show that this type of work is attended by numerous difficulties. Thus
North (1964) observed that strains of Macrocystis from South California
were sensitive to sea temperatures a little more than 20°C for several
weeks, whilst plants from 600 km farther south were able to survive
exposure to 24°C.
Whilst the gametophyte phase poses many questions of ecological
interest, the great productivity of the surface frondage of the sporophyte is evidently well able to cope with regular harvesting.
8. Laminaria
The Laminaria sporophytes are macroscopic structures harvested
either for their food value, or for the extractives they contain. These
large plants alternate in their life history with microscopic filamentous
gametophytes from which the young sporophytes develop after fertilization of the oosphere within the oogonium. Hence a knowledge of
the growth and survival of the gametophytes is an essential preliminary
to studies on the seasonal life of the larger plants.