Interactive effects of elevated temperature and pCO<inf>2</inf>on early-life-history stages of the giant kelp Macrocystis pyrifera

Abstract

Rising atmospheric CO 2 is expected to increase global temperatures and partial pressure of CO 2 in surface waters, causing ocean warming and acidification. These changes may have important consequences for the physiological performance of early life-history stages of marine organisms. In this study we investigated the potential for interactive effects of ecologically relevant levels of temperature and pCO 2 on germination, dormancy and mortality of zoospores of the giant kelp Macrocystis pyrifera, a foundation species of temperate reef ecosystems. Newly settled kelp spores were cultured in the laboratory for seven days in a factorial design with temperature (13°C and 18°C) and pCO 2 (~370 and ~1800μatm) as experimental factors. The two levels of temperature and the low-pCO 2 treatment in our design were consistent with present-day environmental conditions in the kelp forest as measured by autonomous temperature and pH sensors, while the high-pCO 2 treatment reflects an extreme, future acidification scenario. Our results revealed that the combined effects of increased temperature and pCO 2 can significantly decrease germination rates and increase the mortality of kelp spores. Interactive effects of temperature and pCO 2 were detected on spore mortality and dormancy. Spore mortality only differed between pCO 2 treatments at high temperature. In contrast, spore dormancy was higher in the treatment with low temperature and high pCO 2 , which is similar to the environmental conditions experienced during upwelling events in southern California. Our results highlight the importance of considering multiple stressors to understand how the early-stages of foundation species such as M. pyrifera will be affected by global change. © 2014 Elsevier B.V.