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

5 ..· 7 years old. Some were still surviving in April 1975 indicating
that plants can live for 8-10 years. Because earLy conceptacle
layers are obscured in the medulla it is likely that some may live
even longer than this. neH~pine (pers. cOlnm.) told me that some D.
antarctica tagged at Kerguelen in 1961 were still surviving ten yuars
later.
Few D. antarctica can be expected to live much longer. than
ten years because by that time their holdfasts are cQ1l\ple'cely excavated
by animals and the plant is easily dislodged during storms.
Several D. luiLZana tagged in 1972 had three or four conceptacle
layers. Some which survived until 1975 were 8--10 years old. There
is some evidence that D, wiZZana lives longer than D. antarctica, and
this is most likely because animals do not excavate D. wilZana holdfastso
cOmpared to several fucaceae both Durvillaea species are long
Rees (1932) found that under conditions of moderate 1tTaVe
exposure AscophylZum nodosum lived three or four years on average, and
that in sheltered places five year old plants might be found.
The longGivity of some laminarians approaches that of DurviZlaea.
Kain (1971a) found that the oldest specimens in collections of
Laminar'ia hypeY'bo:t'ea from Norway Illere eleven years old, and she
claimed that larger samples would ha.ve revealed even older specimens.
As has been found for species of Ascophyl~um and FUcus (Rees 1932
and Knight and Parke 1950) longevity of Dul'ViUaea decreases with
increasing wave force. D. antaY'ctica grm"ing in areas subj ected to
very strong impact force are on average younger than plan·ts gr.-owing in
more sheltered areas.
10.8
The. numerical density of D. antCU'ctica decreases with diminishing
\'Iave force because of competition from other algae whic~;( become
increasingly abunda.nt as conditions become less exposed. In semishel-tered
places on First Slope at Tautuku the fucoid XiphophoY'a
chond:t'ophyZla (Brown in 'l'urner) Harv. competes t>Ji th D. antarctica for
space in. the Iml1er li ttoral . DuY'viUaea plants growing in selni·'~
sheltered localities are often more heavily grazed upon by fish Chan
are plants in areas subjected to strong wave foy.ce. Rain (1971b)
noted t.ha.t in. areas grazing probably affects the of
Laminaria hyperborea. It is feasible that fish grazing becomes more
intensive with diminishing wave force, and that this contribu.tes t.o
the decrease in density of DUY'villaeao