Elevated temperature and changed carbonate chemistry: effects on calcification, photosynthesis, and growth of Corallina officinalis (Corallinales, Rhodophyta)

Recent ecophysiological studies of coralline algae have highlighted the effects of several environmental concerns, such as acidification and warming of the world's coastal oceans. Among these, elevated temperature might be the most critical environmental factor affecting rocky benthic communities, where coralline algae tend to dominate the habitat. This study was conducted to investigate changes in photosynthesis, calcification, and growth of the geniculate coralline alga Corallina officinalis after 7 d of acclimation to four temperature conditions (13, 18, 23, and 28 degrees C). Calcification rates decreased with increasing temperature in the light, although growth of C. officinalis did not differ considerably under different temperatures. Furthermore, although photosynthesis was largely unaffected by increasing temperature, respiration increased significantly under the highest temperature. These physiological responses are strongly related to the carbonate chemistry of seawater, which is itself affected by elevated temperature. Our results also indicate that C. officinalis exhibits physiological tolerance to a wide range of temperatures, even when increased by more than 10 degrees C above ambient temperature of 18 degrees C. Consequently, if noncalcareous macroalgae are negatively affected by higher temperatures, the ability of C. officinalis to acclimate to these conditions could cause it to become a more dominant species of rocky macroalgal habitats as ocean temperatures continue to rise.