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

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half of ·the s uprali ttoral fringe, together wi t.h the 1l.lidli ttoral and
the sublittoral fringe comprised the littoraL The sublittoral zone
was belo"! ELWS; the sublittoral fringe I-Jas that part of the littoral
exposed only by the lowest tides and during the suck-back of waves.
They claimed that on most temperate and cold water coas
the \-Jorld thesubli'ctoral fringe \vas essentially a zone of large brohln
algae: usually laminarians and fucoids,
Womersley and Edmonds (1952) ammended the Stephenson's schel'rte
because they found i:hat zonation on some south Australian shores did
not fit in/co it na turall y . They proposed tha t the term Ii ttoral be
restricted to the region between the upper limit of barnacles and
MLWN; i.e, the region which the StephensonS called the midlittoral
zone. 'I'hey divided the litt.oral into upper I mid and low, and,
restricted the term sublittoral fringe only to localities where there
was a true fringing zone of algae or ani.mals not extending below
ELWS. In the absence of any true fringing species they deemed it
better to proceed directly from the littoral zone into the upper
s ubI ittoral.
As mentioned in Chapter 4, D. antarctica extends vertically from
about MLWS to a level (depending on wave force) between highest LWN
and MSL. It does not fit neatly into either of che two schemes
described above because it occupies the upper hnlf of the sublittoral
fringe and all or part of the 10Vl littoraL D. liJillana extends
downwards from MLWS to approximately two metres below ELWS. Because
only the upper part of the D. wiZlcma band would come IIlithin the
Stephensons sublittoral fringe it cannot be regarded as a true
fringing species. Its distribution fits more naturally into
Womersley and Edmond's upper sublittoral zone.
D. potatoPUm and Do chathamica, on the other hand, are true
fringing species, occupying the sublittoral fringe 0
In general, the zonation of JJu:pvilZaea spp. fits more naturally
into the scheme proposed by Womersley and Edmonds, them into t.he
less flexible universal scheme proposed earlier by the Stephensons,
10.3
Even from the earliest developmental stages it is possible to
distinguish between young D. antaX'ctica and D. wi Zlana , Cl.lthongh as
has been shown (Chapter 5), both species demonstrate a high degree of
phenotypic varia"tion attributable in large part to the same causi tive
iigents.
Morphological variation is mostly independent of age, but