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

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appears to be gl:eatly influenced by habitat, position on the shore,
gra.zers, and in the case of D. anl;al'etiaa, by the effects of the brown
algal parasite lJerpodiscus dUl'vi Ueae.
Wave action is one of the most-important factors responsible tOl'
morphological variation, and led to the designation of distinctive
but intergrading forms.
Generally the degree to which a given
popUlation extends to\>lards one form or another is a rough measure of the
mean wave action for that. particular habitat..
The:t'e has been some
uncertainty D$ to whether these differen\:.: forms are phenotypic or
genotypic in nature.
Skottsberg (1921: 53) recognised cape and thonged
fOrI\lS as separate species. but I believe that the differences are
phenetic" So too did Mr W.A~ Scarfs, an industrious collector of
New Zea_land algae in the 19305.
In a letter to Robert Laing, dated
November 1938. he discussed the identity of a Du~villaea
specimen that.
had been submitted to Laing for identification. He stated: "Probably
the specimen submitted to you a few months ago is an intermediate.
It is worth while invest.igating this.
Certainly I have seen
variations, as you describe growing on flat shores, exposed to surf in
rough t-Jeather, but partially protected by rocks.
It is an environmental
farm.
Of course you know perfectly well that when growing
on a cliff it is exposed to the streaming effect of the retreating
wave, jus'i:. as much as when it is growing in the channels behleen rocky
islets.
In both cases it becomes thong like, as at Lawyers Head and
the cliffs at Seaview (near Dunedin] .
in these channels it is exceedingly long,
more than 15 feet long and a few inches wide.
At La1Jryers Head ,,,hen grm .... ing
Some of the thongs are
flat beach, or sheltered by rocks it becomes apron like."
But when growing on a
The problem as to whether the differences are genetic or phenetic
can be resolved by the determination of intermediates [i .. c. 'co see if
the differentiation of popUlations is clinal). by determining whether
the extreme forms are interfertile, or by carryIng out reciprocal
tr8.nsplant experiments.
As mentioned in Chapter 5, some shores vlith uniform topography
support mor e.-or-le S5 pU1.-e 5 tapds of one form or anotj)er, but on broken
shorelines, two extreme forms may be found growing in proximity.
example, at Oha.u Point one occasionally finds thonged specimens growing
on the sem .... ard side of rocks, and cape forms on tJle sheltered land-·
ward side.
Most important is that on broken shore.s offering a t .... ide
range of Vlave exposures there is usually a full rang'e of intermediates.
For