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

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areal, but this was to be expected since the sites were cleared at
different times during spring and summer, and differed slightly
in terms of wave exposure and shore topography.
These other seaweeds prevented dense recolonisation by
DurviZlaea in the following winter, by occupying the predominantly
bare areas. Area Sa (cleared October 1972: 28 m 2 ) contained only
274 D. antarctica plants a year after clearing, and most of these were
small specimens inadvertently missed during clearing in the previous
October. However at least 50 plants were recruited in the 1973
winter. Many of these were attached to the coralline turf. Codium
adhaepena. mussels and even the shells of limpets. and were therefore
easily detached during storms. Consequently most of the kelp plants
present after 3~ years, were survivors,of those small specimens
which escaped the clearing process. As the size of these plants
increased, the area of coralline turf declined (Fig. 9.1, column 1).
This may have been a result of shading and/or abrasion by the
DurvilZaea fronds.
The number of mussels (Perna canaliculus and to a lesser extent
MYtiZia edulis aoteanus) exposed after the kelp was cut, declined
over several months after clearing (Table 9.3). This applied
particularly to those areas cleared during the spring and summer.
On Area 9 (cleared 2 November 1974: 21.6 m 2 ) for example, all PePna
disappeared within seven months. Originally many were loosely
attached to the rock, and presumably a local increase in wave action
following removal of the kelp, was the main cause. However I on th is
same area, there was heavy settlement of MytiZis eduZie and
pulez 2 in the autumn and early winter after clearing (Fig. 9.1,
column 3). No comparable recrui tJnent was found in adjacent control
areas, so it seems likely that this was a direct effect of removing
the kelp. Mortality of these small mussels was very high, however.
Large rock slabs which were shifted about in the kelp zone during the
winter of 1974 may have been partly responsible for this; but a more
Ulva was never particularly common on Area Sa, but was important
On three other areas. SpZanchnidium, Leathesia, Hetel'osiphcmia
and RalfsM appeared on some areas and not on others.
2 Formerly knOWn as Modiolus neozeZandicus Ireda1e 1915.