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

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(b)
At Parititahi, 80% of the tagged specimens were lost in 18 monti1S.
Fifty were originally tagged in May 1973, and of these:
five were
lost in a September storm, and 16 Here lost dlU."ing 'Vleek-long StO¥:ll1S
in March 1974. Plants lost ranged in size from 1.04 m to 2.92 m.
At Tautuku, mortality was sixl1ilarly very high (84% in two
years), with highest mortality during the 1974 winter 0
Of the original 25 specimens tag'qed, 16 'VJere lost. by July,. and by
March 1975 only four were surviving.
Mortality was mainly caused by the stipe breaking or tearing
out of the hold£asto Compared to D. antapctiea relatively few D.
willana holdfasts\Olere detached.
7.4 SUMMARY OF RESULTS
Growth is not confined to any particular region of the D.
antarctica lamina.
Generally, growth rate increases towards the
distal end of the lamina or lamina lobe.
Growth rates of individual
D. antarctica and D. willana plants are highly variable. There is
an inverse relationship between r-elative grm~th and plant size.
Largest specimens usually exhibit the slowest rates of growth, such
that in many cases the tissue erodes faster than it is produced.
onderstorey plants grow more slm"1ly than other small plants
in more open and better illuminated positions in the kelp bed.
Thus overall growth rate of small plants is faster on steep shores
where the kelp band is narrow and the thonged form predominat.es,
than on gently sloping shores where many shady sites are found in
the wide band of cape form plants.
Greatest grO\\lth of D. antarotica occurs duri ng late spring
and sml~er; i,e. after the gamete releasing period. Least growth
occurs during winter and early spring.
D. antarctica. specimens infected with the parasite Herpodiscus
durvi Ueae 'grow more slowly than visually uninfected specimens.
Mortality is high for both species. Approximately half of
the marked D. antarctica plants at Ohau Point and Tautuku were s\\Iept
away in 2~ years. At Tautuku, smallest and largest specimens in
the sample had the highest mortalities; whereas at Ohau Point,
mortality appeared to increase with plant size.
At
mm:t.ali ty Nas highest during autumn and winter
'-'Jhen the seas \~ere generally l:oughes'i:, and 10\~e8t during the 5 unune 1: ..