Latitudinal Differences in Thermal Tolerance among Microscopic Sporophytes of the Kelp Lessonia nigrescens (Phaeophyta: Laminariales)

Martinez, Enrique A.
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University of Hawai'i Press
The strong temperature increase during the 1982/1983 El Nino event caused local extinction of many species in large coastal zones of northern Chile and Peru. One brown algal species affected by massive mortality was the intertidal kelp Lessonia nigrescens Bory, with a latitudinal distribution from Cape Horn (55° S) to Peru (12° S). Between extreme localities of this distribution, mean annual seawater temperatures may differ by around lO C. After the massive mortality of 1982/1983, some populations survived in a few localities of northern Chile, such as Iquique (20° S). I tested the hypothesis that these populations represent thermal ecotypes. Those from the north, close to the El Nino impacted zone, should tolerate higher temperatures than southern populations. Microscopic sporophytes, cultivated from spores of plants collected in localities at the north, center, and south of Chile, were subjected to three temperature regimes. Two of them included the same average temperature, but different extreme values. Comparisons of thermal tolerance in the microscopic progeny from plants of the three Chilean localities showed that, at higher incubation temperatures, central and northern thermal ecotypes do have higher survival and growth rates than the ecotypes from the south. At lower incubation temperatures, the growth trend was reversed. Also, as suggested in the literature, sporophytic juveniles seem less tolerant than gametophytic microthalli. However, the differences in tolerance between northern and southern thermal ecotypes do not fully explain the survival of high seawater temperatures such as those of the 1982/1983 El Nino event by the northern populations.
Martinez EA. 1999. Latitudinal differences in thermal tolerance among microscopic sporophytes of the kelp Lessonia nigrescens (Phaeophyta: Laminariales). Pac Sci 53(1): 74-81.
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