A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...
A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...
A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...
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108<br />
This is not the only way that laJflinae are divided" Some<br />
division is simply caused by the laminae tearing or splitting on<br />
sharp objects during storms. This is particularly common where<br />
there are large mussel beds. Narrow thon.gs also arise whe:r:e the<br />
lamina margin is cut or damaged in some way (Pig. 5.12g) (see also<br />
Chapter 9) •<br />
5.4<br />
(a) Effect <strong>of</strong> shore topograph~ <strong>and</strong> wave action:<br />
The degree <strong>of</strong> shore slope <strong>and</strong> surface irregularity exerts<br />
a strong influence on the strength <strong>of</strong> wave action at anyone<br />
locality (Lewis 1964). My observations showed a relationship<br />
beb,leen the external morphology <strong>of</strong> DurviUaea <strong>and</strong> the intensity <strong>of</strong><br />
,,,ave action in different locations. In general there seemed to be<br />
an increase in braiding, stipe length, holdfast size <strong>and</strong> honeycombing<br />
with increasing wave action.<br />
Three morphological types <strong>of</strong> D. <strong>antarctica</strong> predominate.<br />
are referred to here as "high impact", "thonged" <strong>and</strong> "cape" forms.<br />
Intergradation occurs, <strong>and</strong> is dependent on large or small scale<br />
variations in shore topography <strong>and</strong> wave action,<br />
These<br />
(i)<br />
High impact form (Fig. S.6a-c)<br />
Wave force is particularly strong against cliffs on de~p water<br />
coasts that are fully exposed to oceanic swells. The inter-tidal<br />
region at the base <strong>of</strong> cliffs directly facing the waves is subjected<br />
to very strong impact forces as each wave destructs. tl1ater pressure<br />
fluctuates wildly. The impact <strong>of</strong> waves is even stronger where the<br />
cliff face is slightly undercut, because the kineti,· energy <strong>of</strong> each<br />
wave normally expended as a towering column <strong>of</strong> water <strong>and</strong> spray up<br />
the cliff face, is then concentrated in the relatively narrow<br />
confines <strong>of</strong> the intertida.l region.<br />
D. antar'ctica plants growing in such areas are typically very<br />
stunted, their length rarely exceeding 1 m. 'rheir laminae are<br />
deeply cleft into a number <strong>of</strong> narrow (less than 1 em Hide) thongs,<br />
so that the palmat:e region is gr.eat.ly reduced 0 The thongs are <strong>of</strong>ten<br />
thickened slightly at their ba.se <strong>and</strong> along their margins. Any<br />
honeycomb ·tissue is poorly developed. Stipes are propm·tionately<br />
thicker than the st.ipes <strong>of</strong> similar sized plants g"Lowing in cn;'eas
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