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

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Result.s:
Within a week all of the delimpeted areas were covered \'lith a
diatomaceous film, predominantly LycmophoY'Q sp. POY'phYY'Q columbina
appeared six weeks earlier on Area D than on adjacent control rocks,
By October'kNovember 1974, thousands of small «10 em) D,
antaY'ctiaa had recolonised Area A 0.5-0.75 m above the kelp's normal
upper limit. Plants grew thickest on the shady south faces. A
laNn-ltke sward of small plant.s spread inside and onto the roof of
a shallow recess which runs along the southern side. 'I'he
mean density of plants at that time was 47 000 per m 2 , Some small
D, antarctica colonised the top of the rock, and g:cew amongst
POY'phYY'a. These stragglers were O.8~0.95 m above the normal kelp
level. No sinall plants were found growing above the kelp band on
adjacent control sites.
Area B was not as easy to keep free from limpets as Area A.
Nineteen large C. denticulata and C. radians ~ .... ere removed in December,
and the tracks formed by their brolilsing were clearly visible. They
had Obviously grazed away the plants growing highest on the shore.
Where qra.zers were left, and the kelp was cut (Area C), the small
D. antQ~ctica covered the rock between the decaying holdfasts. and a
20 em wide strip above the original upper limit of the kelp.
Despite the fact ·that some limpets invaded Area B. the upper lind.t
of the recolonising sward in that area was, on average, 0.17 m higher
than in Area C.
The delimpeted rock at Ohau Point (Area D) was above the normal
upper level of the D. antarctica band. Several hundred small plants
appeared on the rock, but there was no development of a lclWn-like
sward. Most plants were confined to four small clumps on the south
side. The highest clump was 1,8 m above the normal upper limit of
the kelp, and grew in close association with the high intertidal red
alga Bostrychia a~buscuZa. D. antar'ctica did not colonise the contr'ol
rock nearby, where there were numerous limpets.
During the summer I the young D. antarctica growing above the
normal upper letrel of the kelp band were burnt off. Mortality
\'1a5 exceptionally high 1Ilhen 10\11 tide occurred about midday .. plants
grm .... ing on the top of rocks were burnt firs't, and \'~ere soon follm!ed
by others on northern, seaward and southern faces. By April 1975
a.lmost all young plants had gone. and the rock (especially in Area A)
was covered by Enteromorpha sp.
By mid May most of the survivors
xI/ere growing within a few cm of the norma,l upper lirrdt of the kelpo