A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...

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of D.
antaratiaa across 25° of latitude.
10.5 GROWTH
Although the relative growth rate of a plant, as expressed here, is
generally inversely proportional to its size, some small plants do grow
quite slowly. These are understorey specimens, and their frequency
in any sample greatly influences any mean measurement of growth. It
is important to ascertain the frequency of understorey plants when
comparing mean growth rates of different samples. They are more
cammon on gently sloping shores than on steep shores. This together
with the fact that the marked sample at Ohau Point was free of
HeppodiacuB (other marked samples were heavily infected) accounts for
faster mean growth rates being recorded on the steep slopes at Ohau
Point, than on the more gentle slopes at Tautuku and Oaro.
Seasonal changes in metabolic rate, and seasonal flUctuations in
the amount of frond tissue lost by abrasion or breakage were responsible
for the seasonal fluctuation in net growth of large D. antarotiaa at
Tautuku and Ohau Point.
There was a close relationship between vegetative growth rate and
fruiting period. Declining net growth during au~umn and winter
corresponded with the period when plant metabolism was largely concerned
with production of gametes. Only after gametes were liberated did the
vegetative growth rate begin to increase. Correlations between vegetative
growth and reproductive periodicity have been reported for other
large brown algae. Parke (1948) found that Laminaria sacaharina grew
fastest between March and July (spring and early summer), and that
least growth occurred during the reproductive period between October
and March (late autumn and winter) . Similar observations were made by
Hasegawa (1962) for Laminaria anguBtata Kjell.
As a general rule, sea conditions at Tautuku and Ohau Point are
roughest during winter, with some particularly severe storms occurring
in late autumn and early spring. Damage to D. antarctica and D.
wiZ,Z,ana fronds was most extensive at that time of the year. Results
Clearly showed that mean frond length decreased over the winter.
When HeppodiBCUB durviZ~eae dies down in late winter and early
spring (August-September), it leaves weakened patches on fronds that
tear easily dUring storms. Seasonal fluctuations in net growth of D.
antaPctiaa are more marked at Tautuku where the parasite is common,