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

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analyses. Difficulties in tagging small D. winana plants
effectively prevented measuring specimens shorter than 0.5 m. The
inaccessibility of this species meant that censuses 'V¥ere made less
frequently, so that it was difficult to detect any seasonal flu~~
tuations in gro...,th rate.
Storms during the autumn and winter of 1974 pxactically decimated
the tagged D. wiUana samples at both Parititahi and Tautuku. The
do.til that. were obtained (covering a period of approximately 18 months) ,
revealed no marked difference between grOl.-1th rates of the 'cwo species.
Total length of the fastest 9'rQ(o,ling D. wiZ lana specimens at
Parititahi increased 40% in 18 months (from 1. 49 rn to 2.09 Ill) •
Comparable measurements were obtained for similar sized D. antarctica
specimens growing at Ohau Point nearby. At the other extreme I the
total length of a 2.8 m D, willana specimen decreased 51.4% in 10
months, and again comparable figures were obtained for D. antarctica
specimens of this' size. During the period June 1973 to November 1974,
mean percentage increases in total length, stipe length and stipe
dia.meter of medium sized D. wilZana and D. antarctica plants (the
latter bracketed) were 24.3 (22.1); 18.4 (9.2) ana 14.0 (30.3)%.
Thus there appeared to be no significant difference between the grm~tl1
rates in total length between the two species. However, there were
differences in the growth rate of stipes. Stipes of mediwfi sized
D. willana plants elongated twice as much as those of D. anta~ctica
specimens. The converse applied to the rate of growth in the thickness
of st.ipes.
In general, D. wiZlana plants, like D. antarctica plants, grew
at a rate inversely proportional to their size" Mean leng,th of
specimens comprising the smaller half of the Paxititahi sample
increased O. 27 m in IS months, whereas there was a 1.5% decree.se in
the mean length of specimens comprising the larger half of the sampleo
Comparable measurements for D. willana at Tautuku showed that the mean
increase in length over 18 months for plants longer and shorter than
mean length, were 1.17 and 2.35 m respectively. At Parititahi, mean
stipe 1eng th of specimens comprising the Slllaller hal f of the sample
increased 18 em in 18 months (52.8 ± 3" 4 CUI to 70.8 ± 1.2 em), whereas
the:ce was no significant increase in the length of the stipes of
specimens compriSing the larger half of the sample. Percen·tage
increments in stipe diameter on the other hand, were about the same
for all :rna.rked D. wiUana specimens 0