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

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stipe length, holdfast diameter, the "stipe fraction\! of plant
wei~ht
a.nd the numerical density of plants all decreased with
diminishing wave force. Mean plant weight increased slightly ..
There wo.s no obvious variation in total frond length and stipe
diameter.
Although these samples at Tautuku demonstrated that size
varies with "'lave force r all the plants on First Slope (with the
notable exception of a few speciJnens in the channel which were cape
form) were of the sarlle general form. The laminae of all mature
specimens were moderately to highly divided into thongs, and highly
honeycombed.
The phenomenon of an increase in the division of laminae toli th
increasing wave action also applies to D. willana. Along the
sealrJard edge of shore platforms and on steep coasts, H.s laminae
are highly divided into narrow thongs less than 5 em \... ide. With
lessening \oJave action, the laminae become wider and less divined,
until in semishelte:ced places they are quite like cape form D.
antaJ:'c:tica (Fig. 5.8d,e). Their stipes generally become shorter
and thinner, and there is an increasing tendency for plants to
possess fe~ver lateral laminae.
(b)
Relationship between morpholo~ and vertical distribution:
At Tautuku the thickness of honeycombing in D. antarctica
increased down shore. Mean values for the volume of seawater
displaced per gram of lamina of mature specimens from the top, mid
and bottom of the D. anta~c:tica band on Second Slope wexe: 1.64 ±
0.06, 2.13 ± 0.09 and 2.18 ± 0.10 ml respectively (n=30 in each case).
Specimens with the highest value (3.5 ml/g) were collected immediately
above the D. wilZana band.
D. anta~atica stipes are usually circular or oval in cross
section, although occasionally they have a distinct ridge running
dm~n one side. In general they taper distally, and expand abruptly
into the flattened palmate region of the lamina. Some branch
distally into thickened bough-like branches (Fig. 5 .11a,b) . In
Crogs section these are indis1i:inguishable from the rest of the
stipe. Stipes like these are common at Ta.utuku, and I have also
seen 'chem at Banks Peninsula and Oil Snares Isla.nds This feature
is confined to plants forming the uppet fringe of the D. an.tarctica
belt - plants which are usually distinctly yellolltish by cCl."Iiparison
with darkex green-·brown specimens growing lm'ler down the shore"