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

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(cl D. antarctica extends no north than 54°5 on the
Argentinian coast,
The Falkland Island Current r a branch of the Cold Cape Horn
Current, is deflected north\I1ards along the Argentinian coast, Xo the
vicinity of Bahia Blanca (38°S) it meets the warmer, south-flowing
Brazil Curren,:. The btJO current systeros veer easb.llards and a
convergence zone is established between them 0 It seeIfiS st;:ange that
the kelp does not follm'1 the path of this cool Falkland Island
Current; particularly when on the west coast it follows the Peru
Current for several thousand km, The laminar ian- MacY'ocystis pYr'ife.Y'a
which gr~~s
in most of the places inhabited by DurviZZaea. extends
much further north on the Argentinian coast to 42°S (fuehnemann 1970:
Fig. B) •
Although much of this coast is sandy beach, there are innumerable
rocky outcrops where DurvilZaea could grow~uehnemann pers.comm, 28
November 1975). Conditions may be too hot and dry for D. antarctim
in southern patagonia (a rain shadow area), but this cannot explain
the absence of the kelp from most of the eastern Tierra del Fuegian
coast. At Coquimbo, where the kelp does occur, conditions are much
hotter and drier.
The factor tha.t I consider is most likely responsible for the
absence of D. antaY'otica north of Bahia Thetis in southeast Tierra
del Fuego, is the sharp increase in tidal amplitude along that coast}
At Bah.l.a Thetis the maximWTl range is 3.9 m, At San Pablo, 50 Ja:n to
the northwest, it is 6.5 m, and 80 km further up the coast at Puerto
Rio Grande it is 7 ro. According to Doty (1957) and Knox (1960) the
tidal amplitude at the mouth of the Chico River in Patagonia is 12,4 m.
In general. tidal amplitude on DupvilZaea coasts ranges from 1
to 3 rn. At high tide the laminae of the largest plt,nts float on the
surface, and are therefore fully exposed to the sun. If, hOHever,
the kelp band is in the Im