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

15
added to the top of the tube. The sinking rate of the ova, clearly
visible against the white background, was then measured. Five
runs were made for each species.
(iii) Desiccation experiment
Equal sized lamina samples of 15 D. antarctica and 15 D,
willana
(each 75 x: 75 :m.rn) were desiccated in a drying oven set at 3SoC.
Dried calcium chloride \\l'as a.deled to 'che bottom of the oven to prevent
any marked increase in hwnidity. Initially, each sample was blotted
dry and weighed, and weights were subsequently recorded every 1S
minutes for three hours prior to drying to a constant weight" Water
loss was measured 'as a percentage of total water content.
2. 5 ASSESSMENT OF WAVE FORCE
Wave force, often simply referred to as exposure, is both
difficult to define and to measure.
Precise definition is difficult
because the ternl is I in itself, a collective term of various featu.res
of water flow (KirJ~ 1971: 374) . Measurenent is difficult,
especially on outer coasts, because of the major complicating factor
caused by variable shore topography.
On the Kaikoura l?eninsula coas tit \.,>a5 p()ssible to use maps
of wave force that were drawn by Rasmussen (1965), and based on a
subjective scale containing six categories (Table 2.3).
Table 2.3
Rasmussen I s subj ective scale of \, ... ave force.
o
I
II
Glassy smooth, little or no swell~
Ripples, very gentle swells, enough to effect the
organisms no more than 6 em above the d.bso1,ute level.
Waves wi th repetitive pat'terns and/or gentle s\,le1ls strong
enough to ca.rry water several inches up vertical faces ~'lii:l1out
breaking.
of
III Waves that break on ve:ctical, and nea:c ve:l:'tice.l surfaces I or
that crest or break over sha.llows.
IV
V
Waves that break throwing horizontal spray on meeting
resistance. These have a and
effect well above the tide level.
Waves that throw spray vertically on meeting resistcl.Uce)
causing maximWl1 pounding effect.