Tolerance to air exposure should be an important feature in determining the geographic distribution of seaweeds. Two sibling kelp species with contrasting latitudinal distributions were selected to test the relationship between their distribution and air exposure tolerance: Lessonia berteroana distributed between 18° and 30°S and Lessonia spicata, which is found from 29° to 41°S along the Chilean coast. This region presents a latitudinal gradient of environmental variables, which leads to an increase in air exposure as latitude decreases. Therefore, populations of L. spicata are likely to be exposed to lower desiccation levels than those of L. berteroana. To assess adaptation to air exposure, early stages of development of these species were exposed to air daily for 0, 0.5, 1, and 2 h, and the activities of two antioxidant enzymes (ascorbate peroxidase and catalase) were measured. Results showed that L. spicata spores ceased their postgermination development when exposed to 1 and 2 h of air, contrasting with L. berteroana, in which spore development was not abruptly stopped as for L. spicata. In addition, the apparent inactivation of the antioxidant enzyme catalase in both species strongly suggests a lower buffering capacity to an excess of reactive oxygen species (ROS) triggered by air exposure. Thus, air exposure seems an important factor determining the northern geographic limit of L. spicata.