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

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CHAPTER SEVEN
GROWTH AND MORTALITY
7.1
.This chapter. deals with grm\ltb l
morto.lity and longevity of
Durviltaeao Although it is largely concerned with Do anta~ctica,
smne compa~aLive data are presented for D. wiZlana. In contrast to
the quantitative data which fo 110\01
(Chapter 8). the data obtained
here \o,Ie17e derived from field measurements of marked plants of both
species, and not from popUlation studies.
Growth as defined here, is concerned with net tissue production
measured at intervals over the annual cycle. By selecting a
number of parameters (;Fig. 7.1) for both species, differences in
growth between the main organs (laminar stipe and holdfast) were
aet:ermined on the basis of locality, season and other factors. It
proved to be ilnpractical to measure increments in the Ne"t weight of
individually marked specimenso However, as shown in a subsequent
section (Chapter B), there was a close correlation between both total
plant length and stipe diameter and plant weight. stipe length \'las
not a representative measure of plant we.'lght since most siz.e classes
contained plants with a wide range of stipe lengths (Table 7.1).
While the developmental stages of both species have been
described (Chapter 5), accurate ageing of plants was not possible
in either species, and the use of size classes was necessary.
ever, a.s has already been mentioned, size often bears no relationship
to age.
It was important to establish whether the:ce was any localisation
in growth in the lamina. This t'las measured for D. antarotioa by means
of a series of marked plant experiments in the field,
Using other samples of marked plants, attempts were made to
determine mortality rates at several widely separated localities.
The effects of age (where possible) habitat, sea condition8 and
other fac"tors on rooy·tali ty and longevity were assessed.