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

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total length closely resembled that based on weight, and it was
therefore considered expedient in subsequent samples to define
size struct:ure in terms of total plant length"
The size structure of samples from widely separated local
in New Zealand was fairly consistent (Pig. 8.2) despite the fact tl1at
they were collected at different seasons. Frequency increased
steeply with plant size until plants were apprmtimately 0.5 TO long,
and thereafter abruptly declined. All cw::ves were skewed strongly
to the left" In ea.ch sample " 40-60% of specimens were shorter than
0.5 m and \tl(~ighed less than 5% of the total standing crop. \I1hereas
large plants comprised only 2-5% of the sample but formed over half
the standing crop.
There was little seasonal change in the size structure of
s~mples from the same locality (Fig. 802, left column). A slight
recruitment of small pla.nts was detected in winter (June/July) J
but apart from that there was little difference between the graphs.
There '-las certainly no evidence of any large scale recruitment of
small plants during winter and spring, such as occurred in recolonising
swards on experimentally cleared areas (Cnapter 9).
The number of plants borne on each holdfast mass was coun'ted
in all D. antaratica samples, and in one large D. willana sample.
It \,las thus possible to calculate the frequency of holdfasts
supporting a certain number of stipes, In all samples results were
similar to those data presented in Table 8.1. Most plants with
discret.e holdfasts were small specimens shorter than 0.5 nl. Large
specimens (longer than 4 m) were commonly attached to holdfast
masses which supported three Or more other plants.
B.3 SEASONAL FLUC'l'UATION IN STANDING CROP OF D. AN'l'Ali.CTICA
standing crop of D. antG.1YJtiaa on eight transects at Tautuku
2 -
ranged from 15,3 to 33,0 kg/m (Y ~ 24.2 ± 1.9 kg). The~e was no
obvious correlation between measurements and the gradient of wave
force
across First Slope, so that in this small area it seemed
unlikely that wave action was responsible for this variability,
There \V'as, however, sbme evidence of seasonal fluctuation in standing
crop values (1':ig. 8.3); the pattern at Tautuku being for an increase
in standing crop after spring to reach a peak in midwinter, followed
by a decline in winter and early spring.
This was simila_l:: to t:hB