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

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such conditions do noi:. occur on exposed rocky coasts around Nevi
Zealand. Insofar as factors responsible for the local distribution
of DuY'vi"lZaea are concerned. salinity would appear to be Ilnlinport:ant:.
(Vi)
BioZogioo.l competition
In many areas, and on the Westland and I,o,est Auckland coasts in
part.icular, the mid and 10'l'ler littora.l is dominated by several species
of mussels and Do antQPctica.
At 'VJoodpecker Bay, Westland, there are large beds of Per>na
C!analiculus Gmelin. On the outermost rocks where wave force is
strongest there is a band of D. antaPctioa with patches of Perna
interspersed beuqeen the holdfasts. With increasing shelter (tot'lards
the shore) the kelp becomes sparse, and Perna covers most of ·the
available space (Fig. 4.1d). In semisheltered conditions. D.
antarctica competes unsuccessfully agaihst the mussel. Plants are
small and axe usually d.ttached to mussels. Eventually the Dux'viZlaea
holdfast prevents the mussel from feeding properly, and the mllssel
breaks loose. The surrounding mussel bed spreads outwards and
soon fills in the small space.
It appears that in certain semisheltered areas, mussels are
co.pable of excluding D. antapctioa I or at least preventing the kelp
from forming a continuous band. At other semisheltered areas,
where there are no large mussel beds the kelp grows abundantly.
In some places the distribution of D: anto.Y'ctica appears to
be influenced by Ca:r>pophyZlwn spp. On very exposed headlands and
islands on the east Auckland coast the lower intertidal is dominated
by C. a:ngustifoZiwn. D. antarctica forms a narrow band above the
CaYpophyUwn, o,nd appears to be almost. ous'ted by the fucoid alga
(Fig. 4.1b). Near Cape Maria Van Dieman, Johnston (1966:51) noted
that D. antarctica dominated only in areas II/here ItlaV~ force was
very strong. In slightly more sheltered places he found C.
maschalocarpwn to be dominant. At Kaikoura, D. antarctica is
abundant \'lhere wave action is strongest, but in many channels that
are afforded some shelter and appeax' to be suitable habitat for
lJur>vilZaea, the lOVJ