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

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sampling error l , and to eliminate any seasonal effect. Numerical
density in this instance therefore refers 'co those pla.nts \'lhich
\-lere longer than 1 tn. Nu:roerical density declined I'lith diminishingwave
force. At Tautuku, values declined from 7.8/m 2 to 2.n/m~
inshore across First Slope. On a much wider scale of wave action,
numerical density was found to be lower in semisheltered habitats.
such as Oaro and Ringaringa than at Sethells Beach or Ohau, Point
t\lhere wave action was very oS trong .
This t:cend was also made Clpparent by measuring the percentage
of the rock surface that was covered by holdfa.sts. Across First
Slope, percentage cover decreased from 23.6 to 4.8% (Table B.2)
There did not appear to be any correlation between the
variability of standing crop values (as kg/m 2 ), and the wave force
gradient a.cross First Slope. Samples collected over a mu.ch \dder
range of wave force revealed that standing crop did decline with
diminishing \-lave action. In general, standing' crop \-la5 lowey on
gently sloping shores. or on irregUlar rocky shores, than on s'ceeper
Slopes where wave action was much s'tronger. At Ohau Point and
'l'.,utuku, for example, standing crop exceeded 20 kg/m 2 i while values
were nearly 50% lower at Ringaringa, Wainui and Oaro. An i,ntermediate
value of 15.3 kg/m 2 was measured on the uneven Kean Point
transect; where there was a variety of tllave exposures. Standing
crop did not continue to increase over the full range of increasing
wave force. In areas of extreme impact force, such as the southwest
sides of cliffs at Tautuku, relatively 10\-1 values of 3.7 and 4_0 kg/m L
were measured.
The relationship between plant size (A), standing crop (B) '"
numerical density (e) and wave force (D), may besb be described
diagrammatically as in Fig. 8.S. The general 'trend ;:,ppears to be
for plan't size to decrease with increasing wove action, but for
numerical density and standing crop to increase over much of the range
of inc~easing wave action. However, II1here wave action becomes
exceptionally strong, both density and standing crop decline.
When conditions tllere rough it t