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

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(d) Numex~cal density:
While st.anding crop increased, nillllerical densi ty rapidly
declined (Fig. 9.1lc,d). At Kean Point densi·ty of plants declined
from 7 OOO/m2 in the spring of 1973 to 1 OOO/m 2 in the following
autumn. 'This. rapid thinning was partly caused by a fe\17
plants forming a canopy above, and thus shading the majority of
plants with slower growth rates. Many small plants in the understorey
were enveloped by the rapidly e)tpanding holdfast t.issue of
larger , OJ::" were grazed by fish, isopods and limpe-c:s" Strong
\lIave action detached many. Nevertheless, the density of plants in
:cecolonising swards was sufficiently high that many holdfasts fused
to form large composite holdfasts supporting 10-15 plants and
occasionally as many as 30 plants. This was a significantly higher
number of plants po·r holdfast mass than in adjacent control areas.
The size distribution of recolonising plants was similar to the
size distribution seen in natl1ral stands, i.e. large numbers of small
plants and relatively few large plants meant that the size frequency
curves \oJere strongly skewed to the left (Fig. 9.12). Periodic
sampling of recolonising swards also revealed a second, although much
smaller recruitment in the second winter (Fig. 9.12). There \lIas
little evidence at either Kean Point or Tautuku, of any significant
recruitment in the third winter season.
9.4 ~FFECTS OF DIFFERENT HARVEST!NG TECHNIQUES
(a)
Culling was carried out in 4 areas: Ie, 5b and 6b at Tautuku ..
and at Ohau Point. Plants longer than 1 rn were culled from area 5b,
while in the other three areas the size 1 imi twas 0.5 m.
Smaller plants grew rapidly after the larger plants had been
In area 6.b, fur example, there xl7as a rapid linear increase
in total plant length, stipe diameter, stipe length and holdfast
diameter (Fig" 9.13). Similar results were obtained ih the other
areas. In each case, the small plants in culled area.s grew much
faster than small pla.nts in untouched O.reas nearby_ Hrn.1ever, they
did not grow as rapidly as those plants recolonising areas that: had
been completely clear.8ao
When invest.igating the mortality of small plants culling,
it "ilJas import.ant to differen1:iab:'! behleen those specimens \vith discrete