Lower and upper survival temperatures of microthalli of 25 species of South American Phaeophyceae isolated from central Peru (14 ~ S) to the Canal Beagle (55 ~ S) were determined using 2-wk exposure for the upper and 4-wk exposure for the lower limit. All species survive 4 wks at -2 ~ With respect to the upper limit, species reported only from southernmost South America tolerate 19.9 to 24.5 ~ (n = 8), and species occurring from Cape Horn to central Chile 24.6 to 27.4 ~ (n = 7). Three species that occurred as far north as northern Chile and Peru before the 1982-1983 E1Nifio event, and whose northern limit was dramatically shifted southwards in 1983, tolerate 20.8 to 25.3 ~ whereas five species that have survived in Peru tolerate 25.6 to 28.5 ~ Tinocladia falklandica which tolerates 27.8 to 28.1 ~ but lives only in southernmost South America and Striaria attenuata, which tolerates 31.6 to 31.9 ~ but occurs at ca. 42 ~ S, are exceptional. Their high temperature tolerance may have no adaptive value in South America. They are restricted to the cold-temperate region due to low temperature requirements for reproduction or for reasons yet unknown. In general, the northern distributional limits of the Phaeophyceae studied along the temperate Pacific coast of South America are reproduction boundaries, except in E1 Nifio years when they are redefined according to the species' upper suvival limits. Temperature tolerance of isolates from northern Chile and Peru agrees well with maximum temperatures reached during the 1983 E1 Nifio.
Inroduction
The temperate part of the Pacific coast of South America extends ca. 6000 km from northern Peru (5~ to Cape Horn (56 ~ The benthic marine algal flora of this region is characterized by species poorness (ca. 400 spp., ca. 150 Phaeophyceae), high endemism (ca. 30%) and an un-