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

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CHAPTER EIGHT
POPULATION STUDIES
9,1
Recent. industrial int.erest in the extent of WeH Zealand's
seaweed resources has emphasised the need for information concerning
the standing crop of DurviZZaea. During the course of this study,
an attempt was therefore made to estimate standing crop. This was
based almost entirely on 12 D. antarctica samples which collectively
weighed 6.1 tonnes, and covered 53 metres of shoreline. All
transects, from which these samples were "taken, traversed the D.
antarctica belt, and included a wide variety of shores.
The minimum size of any sa:caple which is truly representative
of the total standing crop is, however. not known and may far exceed
a sample of this size. Nevertheless, in the absence of any other
measurements of DurvilZaea standing crop, these estimates may at
least serve as a guide.
since samples came from a variety of habitats, and were
collected at different times of the year, it was ilnportant to
establish whether any variability in standing c.-rop val ues was
attributable to habitat and/or seasonal differences. In the event
that a seasonal pattern proved to be apparent in the standing crop
data, then it was important to determine whether this was caused by
seasonal changes in such factors as mortality, growth rate and
population structure.
B.2 POPULATION STRUCTURE
In the absence of any satisfactory aging technique, population
structure was described in terms of plant size. Initially stipe
diameter, stipe length, total length and individual wet weights were
used to segregat0. 450 D. anta~ctica plants into arbitrarily selected
size classes, and the frequency of specimens in each class was
calculated (Fig. 8.1) 0
Individual wet weights Here the most accurate
measure of size, but this was a tedious parameter to measure when
dealing with large samples of matux-e specimens. 'fhe curv~ ha:.:;ed on