BIOLOGY OF SEAWEEDS OF ECONOMIC IMPORTANCE
223
primary production by benthonic marine algae has been investigated
by Bachmann and Odum (1960). Jones (1960) studied the accumulation of radio-ruthenium by Porphyra Zuciniata. The mechanism of
uptake of zinc-65 by Ulva Zuctuca has been described by Gutknecht
(1961). Zinc accumulation was an active process related to the rate
of photosynthesis and is governed by pH and the zinc concentration of
the medium. Freshly killed Ulva thalli initially absorbed more of the
element than living plants. Mauchline and Templeton (1964) have
recently reviewed several aspects of the distribution of artificial and
natural radioisotopes in the sea and their uptake by plants and animals.
C. Browsing by animals
The competitive interaction between browsing herbivores and
seaweeds has been studied for many years. Some of the more striking
results in this direction have come from large-scale experiments
carried out on the shores of the Isle of Man (Jones, 1948 ; Lodge, 1948 ;
Burrows and Lodge, 1950; Southward, 1953, 1956). I n one of these
experiments an area of shore 10 m wide and 150 m in length was
cleared of all vegetation and Iimpets ; the area extended approximately
from M.H.W.N.T. to M.L.W.S.T.
Recolonization then followed
successive stages, starting with a diatom film, then a dense cover of
green algae (Ulothrix, Ulva, Enteromorpha). Germlings of fucoid algae
developed under the green algae and resulted in almost pure stands of
Fucw species after about 2-3 years, consisting of Fucw spiralis,
P. vesiculosw, F. serratw, and of hybrids between them. Somewhat
similar results have been obtained in clearance experiments carried out
at other localities in the Isle of Man and on the Devon coast (Boney,
unpublished observations). In this last case, removal of limpets was
made from an area of shore in the region of M.T.L. 4 m wide and 10 m
in length, and devoid of fucoid algae. As a result of the recolonization
stages almost pure stands of Fucw spiralis and Fucw vesiculosw were
obtained. Continued observations at each locality showed a re-invasion
of the cleared area by limpets which appeared in increased numbers,
showing rapid growth under favourable conditions. The gradual decrease in the fucoid population which then followed was due to the
detachment of the old plants and the absence of any recruitment
because of the limpet population browsing on the sporelings. In
addition to their effect on the young plants, the limpets have been
observed to feed on the stipea and holdfasts of older plants, and probably
weaken them sufEciently to cause their subsequent detachment. A
similar weakening effect is thought to be due to the browsing action of
Patina pellucida on the stipes and holdfasts of Laminaria species (Kain,
223
primary production by benthonic marine algae has been investigated
by Bachmann and Odum (1960). Jones (1960) studied the accumulation of radio-ruthenium by Porphyra Zuciniata. The mechanism of
uptake of zinc-65 by Ulva Zuctuca has been described by Gutknecht
(1961). Zinc accumulation was an active process related to the rate
of photosynthesis and is governed by pH and the zinc concentration of
the medium. Freshly killed Ulva thalli initially absorbed more of the
element than living plants. Mauchline and Templeton (1964) have
recently reviewed several aspects of the distribution of artificial and
natural radioisotopes in the sea and their uptake by plants and animals.
C. Browsing by animals
The competitive interaction between browsing herbivores and
seaweeds has been studied for many years. Some of the more striking
results in this direction have come from large-scale experiments
carried out on the shores of the Isle of Man (Jones, 1948 ; Lodge, 1948 ;
Burrows and Lodge, 1950; Southward, 1953, 1956). I n one of these
experiments an area of shore 10 m wide and 150 m in length was
cleared of all vegetation and Iimpets ; the area extended approximately
from M.H.W.N.T. to M.L.W.S.T.
Recolonization then followed
successive stages, starting with a diatom film, then a dense cover of
green algae (Ulothrix, Ulva, Enteromorpha). Germlings of fucoid algae
developed under the green algae and resulted in almost pure stands of
Fucw species after about 2-3 years, consisting of Fucw spiralis,
P. vesiculosw, F. serratw, and of hybrids between them. Somewhat
similar results have been obtained in clearance experiments carried out
at other localities in the Isle of Man and on the Devon coast (Boney,
unpublished observations). In this last case, removal of limpets was
made from an area of shore in the region of M.T.L. 4 m wide and 10 m
in length, and devoid of fucoid algae. As a result of the recolonization
stages almost pure stands of Fucw spiralis and Fucw vesiculosw were
obtained. Continued observations at each locality showed a re-invasion
of the cleared area by limpets which appeared in increased numbers,
showing rapid growth under favourable conditions. The gradual decrease in the fucoid population which then followed was due to the
detachment of the old plants and the absence of any recruitment
because of the limpet population browsing on the sporelings. In
addition to their effect on the young plants, the limpets have been
observed to feed on the stipea and holdfasts of older plants, and probably
weaken them sufEciently to cause their subsequent detachment. A
similar weakening effect is thought to be due to the browsing action of
Patina pellucida on the stipes and holdfasts of Laminaria species (Kain,