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

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buoyancy. A highly honeycombed D. antarctica lamina is superbly
adapted to st.rong \lIavc force, whereas large stalked vesicles are
easily torn loose on areas where there is strong' surf.
Species often occupy a greater diversity of habita'ts in the
centre of their geographical range than at their margins. This is
because the conditions for life at 'che limits of Lheir range are
less favourable, or much more localised. SV.i3xdson. (1949)
for e](ample. found that the range of habitats of several bird species
became less diverse tOlilards the limits of their range. Often there
are dwarf forms at the extremes of a species range (Allee and Schmidt
1.951~ 156) .
Near the northern limit of its ri.'mge in New Zealand, D.
antarctica plants are small and confined to the most exposed islands
and promontories. Further south (south of 45°5) plants are much larger
and grow in a wide range of habitats;' e.g. on stewart and Auckland
Islands the kelp grows in calm conditions inside inlets and harbours.
There is little habitat fOr Durvillaea between 50 0 S and the
northern limit of drift ice. What information is available from these
small islands suggests that the decrease in plant size and increasing
patchiness of D. antarctica near the northern limit of its range is
not reptila ted in the south. This may be caused by wa ter temperature
being the principal limiting factor in the north, whereas its
distribution in the south is stopped abruptly by the ·noxthern limit
of drift ice.
Other New Zealand brown algae exhibit latitudinal varia·tion in
plant size and habitat diversity. CarpophyUwll maschaZocarpum at its
southern limit (Banks Peninsula on the east coast) grows mainly inside
bays and inlets, and plants are small. In the North Island ii:
occupies a much wider range of habitats and plants are much larger.
In the northern hemisphere at the geogra.phicaJ. limits of its
rqng~
, PuCU$ disticuB L. is often represented by only one or
two distinctive forms confined to restricted habitats. In the centre
of its geographical range it has a wide range of forms and grm-Is in Q.
variety of habitats (Powell 1963:70).
Introducing a paper concerning the speciation of the genus Fucus
and related genera¥ Powell (1963:63) stated: "The large marine algae
a.t·e a very difficult group to reduce to systematic order. Many of the'll
are highly plastic (more so than any other group of plants and
C:i\1,imals) and widely distributed, and bhow profound modifications; . ,.