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

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below' the violent \..,ave action in the lower littoral and sublittoral
fringe. Closer to the surface fish are in danger of being
flicked out of the water by the thrashing kelp fronds, On two
separate occasions. at Ohau point I saw this happen to the sco:q)le>n
fish (Scorpena car,dinalis Richardson). 'L'he fish probably have a
preferred minimum depth at which they will feed. The distinct graze
line in the Do
antarctica sward at Ohau Paint possibly represent~
this minirtlum depth at high tide 0
Young D. wi Hana may survive in the sublittoral because they
are a less attractive food item than Do antarctica. Laminae of small
D, wiZlo:na are relatively thick and ·cough. Many isopods and
arnphipods that readily feed on D. antarctica will not eat D. wiZlana.
One Dupvillaea species does not appear to determine the upper
or lower limits of the other.
The lower limit of D. antarctica is
much the same in areas where that species grows aione, as it is in
areas where both species occur. Plants recolonising two areas
where D. wiUana was cleared were predominantly D. wilZana. In a
sample of 280 small plants from such an area a-t Tautuku, 272 were
D. willana, Similarly D, willana did not invade areas where D.
antarctica had been cleared. Only in the narrow transition region
between the two kelp bands were small specimens of both species
found growing close together. The zonation pattern is clearly
established when plants are very small, perhaps even at the germling
stage.
At Kaikoura the upper limit of young D. antarctica growing on
areas previously cleared was slightly higher than the original upper
level of the .kelp band. At 'rautuku, the pattern was quite the
reverse. On First Slope, the top level of the recolonising swards
\'laS significantly lower than the normal upper limit of the kelp
band (Fig. 9,15). There was nothing to suggest that ~he depressed
upper level of the recolonising swards was caused by limpet grazing.
Large limpets were less common at Tautuku than at Kai]{Qura. Unlike
the Kaikoura situation, very few small D. antarctica pla11ts at
Tautuku Here burnt during the summer 0
Measu:cements of the highest levels of recolonising D. anto:rc-tica
stolards at Tautuku and Kaikoura (Table 4.2) showed that there Has little,
if any difference bet~"een the highest level s of the :t'ecolonising
SHards at the two loca.lities" However, wherea.s the upper 1 inti t. of
the swards at Kaikonra .~etract.ed approximately 0.5 mm over the
SUlM\er I the upper lind t of the stvards at TautlJ.ku remained more-or-less
constant.