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

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the huge populations of large limpets, It is hardly surprising
that DurviZZaea has not become established on cold or warm temperate
south African shores,
(e) The absence of D. antarctica from Tristan da cunha L:
There is no DurviZlaea on Tristan da Cunha, but xli: grows
abundantly on Gough X, 370 krn to the southeast. Chamberlain (1965:
178) sta.ted that algal zonation on Gough L is typical of the subantarctic
pattern, whereas that of Tristan da Cunha has more in
common wlth South African shores. This she claimed corresponded with
the fact that Gough I. is well south of the Subtropical Convergence
whereas Tristan is near its mean position. I do not consider that
this, in itself, is an adequate explanation for the floristic
difference between the two islands. The Chatham Is also straddle
ll:he Subtropical Convergence, and two DurviUaea species grow there
in abundance. The nearest popUlation of DuTviZZaea to the Chatham
Is is much further away t.han the distance between Tristan and Gough
Islands. As mentioned earlier, differences in sea temperatures can
offer no simpl~ explanation. Although Tristan is warmer than Gough,
temperatures there are still lower than in other places Nhere
DurvilZaea grows.
Doth islands are partly under the influence of the Cape Horn
and Falkland Island CUrrents. Baardseth (1941:157) calculated that
the Cape Horn Current would carry "drifting matters" across the
South Atlantic to reach Tristan in 120 days. It is unlikely that
the absence of Du:t"ViUaea on '}~ristan
of ocean currents 0
can be attributed to the pattern
Laminaria paZlida grows on Tristan da Cunha but is absent from
Gough Island. On Tristan this alga extends up into the narrow
littoral region (1.05 m between neaps) to about MLWN. One can but
speculate as to ~lhether this larninarian prevents D, antarctica from
becoming esteblished. Nowhere do the two kelps grm., together.
(f)
Islands:
Delepine (1963) suggested that the alga is absent because these
islands lie north of the Subb::opical Convergence. As mentioned
earlier I I do not th ink that this alone is an adequate explanation,
rt is perhaps significcmt: that Laminaria pall'ida grovls on l:hese