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

15S
of the Ohau but these were easily identified, and
could be excluded from calculations.
Mortalities of the smallest. and size
tha·t of the entire at Ohau Point are illustrated in 1.
and may be with the data from Tautuku 7.14) • l:-.t
Tautuku, the three curves in were t the
size I the smallest then the entire
AtOhau
the
again the mortality rate of the
size class was less than that measured for the entire
The reason for this difference can be seen in Fig 7.19. Instead
of a "u" shaped curVe, the at ohau Point was for
mortality rate to increase with size. Therefore, medium sized
plants at Ohau Point had a
ra'ce than small plants"
Data Ohau Point were less useful than Tautuku data for
stUdying seasonal fluctuations in mortality. Persistent easterly
and the fact that censusing was
to
spring tides, meant that censuses at Ohau Point were more
and less frequent than at Tautuku. More however, was
the fact that the composition of the Ohau sample changed
throughout the course of the study.
This was because marked plants at Ohau Point grew in a
of wave exposures, Mortality was highest in areas where wave
was and the sample was I with time, domina ted
by growing in semisheltered positions such as on the lee
side of boulders. The obtained at Ohau Point
(Table 7.6) therefol':"e
the overall mortality
of D. antarotiaa in that coastal area. This trend did not occur on
First at Tautuku, because "tIl the marked plants \'lere exposed
to much the same degree of wave force.
There was less fluctuation between summer and winter mortalities
a.t Ohau than at Tautuku. Mortality at Ohau Point was also
highest
during
(Table 7.7).
summer (Table 7.6). and not, as was the case at Tautuku,
was caused a
of small
late and summer
During the 1972-73 summer for
e~.amp~e,
58% of the
lost at Ohau Point were shorter .ti1an 0.75 m; whereas the
autumn and , plants this
only 36%
total
on the other exhibited a