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

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Attempts to cross ... fertilise thonged ~'Jith
cape form D. antaY'ctica
in the laboratory \.... e:ce successful, and the resul tan t SfJorelings were
indistingu.ishable from those obtained by crossing parents of the saIne
form.
Unfortunately attempts to transplant D. antaY'otioa behJeen senli·­
sheltered and very exposed habita.ts failed because fish ate all of
'che transplan'cs.
Do
Efforts by Asensi cmd zizich (1972) to shift sloall
anta:rctica to neN habitats were also largely unsuccessful.
The largest size attained by D. antaJ:'otica varies with wave force,
but this need not necessarily be caused by differences in growth rate.
Mortality increases with wave force, and the small size of high impact
plants is because plants are very young.
None of the high impact
specimens collected on the most exposed face of the cliff illustrated
in Fig. 5010 had conceptacles, whereas on the less exposed face 32%
of the thonged plants had at least one conceptacle layer.
The blades of D. antarctica attached along the upper fringe of
the kelp band sweep back and forth over the abrasive zones of barnacles
and mussels above the kelp, Cl.nd on sloping shores they bear the full
brunt of each receding wave.
They are also subjected to strong impact
forces when swells crest over the back of the reef or slope and
approach the kelp band from higher up the shore.
As described in
Chapter 5 the morphology of plants along the upper fringe of the D.
antarctica band differs from that of plants lower down the shore.
Their stipes are often divided distally into several bough-like branches
each supporting a major division of the lamina (Fig. 5"lla,c) and they
have a more battered appearance.
These features are attributable
to the strong impact force of waves along the upper fringe of the kelp
band.
The increase in the length of D. antarctica sti.\ ·~s
down shore
is an adaptation that prevents the laminae of plan ts a:'ctached Iowan
the shore being shaded by fronds of plants growing higher up.
gently sloping platfo:rms a tangled mass of thongs up to 0.3 m thick
often accmnulates in the low littoral at low tide.
On
With long stipes
it is possible for plants growing at that level to lift their laminae
above such tangled masses,
Honeycombing in D. antarctica increases down shore because at
high tide the blQdes of plants attached lowest on the shore are beneath
1-2 111 of water (depending on conditions), whereas t.l1e blades of plants
at the top of the l