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

138
Conceptacles first appea.t in subterminal regions, and in D.
antarctica, they usually appear first in a honeycombed portion of
the lamina. In D. wiZZana conceptacles invariably develop on the
p:cimaxy lamina before any of the lateral laminae. As the plati"t
grO'\'lS older, the area covered by conceptacles spreads prOJ(imally and
distally, and out to the lamina margins. LaminEle of some o'ld
specimens (5 years+-l are almost completely covered with conceptacles
at a density exceeding lOO/crn 2 , Samples taken at intervals alon.g
the lamina contained conceptacles at about the same state of development.
It therefore seems unlikely tha t there is any VJave of
conceptacle development along the lamina,
Because conceptacles contain oogonia at various stages of
development. it is difficult to estimate the number of ova that an
individual conceptacle may produce. If a piece of la.mina is left
undisturbed for several hours in a culture dish then "the ova that
accumulate in small mounds beneath the ostioles may be counted. A
D. wiZZana sat.'lple collected in June 1973 released a mean number of
115 ± 16 ova per conceptacle overnight (n=12. range = 18-145), l~e
mean density of conceptacles on this sample VIas 126/cm 2 , imd the
surface area of the plant was estimated to be 4 m 2 • Thus overnigh t
a specimen this size is capable of producing approlc.imatl'lly 120
IIIUII0rl ova. presumably an even larger quail tl ty \\lould be produced
over the entire reproductive season.
Analyses of frond samples from Tautuku and Kalkoura showed that
D. antarctica plants released gametes in winter (St(:)e "D"
in Table 2.2). At Kaikoura, during the years 1972-75 inclusive.
gamete release conuoenced in April or early May and ceased in ea:t:ly
September. The peak releasing period \\10,S in July or early Augusto
At Tautuku t.he pattern for D. antarctica was similar, exc~pt that
the reproductive period was three to four weeks longer.
The 'Celeasing period may, however p vary from yeCl.r to year, In
1976, for example, D. antal'ctica at both Akaroa' Heads and Kaikoura
were releasing as early as mid-March, 1.:\"0 months earlier than in
t~e
previous four years,