| Summary: | Includes bibliographical references (p. 36-42). Future levels of atmospheric carbon dioxide, currently at 380ppm are predicted to reach 1000ppm by the year 2100 and the accompanying increase of dissolved CO_ in the oceans will result in an overall decrease in seawater pH. Most research on ocean acidification has found reduced calcification in animals that create calcium carbonate (CaCO_) structures, but few have focused on photosynthetic coralline algae, such as those prevalent in kelp forest ecosystems. Here, we compare photosynthesis and calcification in three of the dominant species of geniculate coralline algae along the coast of California, Bossiella californica, Calliarthron tuberculosum and Corallina officinalis, with the purpose of identifying how they will respond to elevated pCO_. Specifically we conducted short-term exposure experiments by subjecting algae to two pCO_ levels, 380ppm and 1000ppm, under a range of irradiances for 2.5 hours during bottle incubations. Construction of photosynthesis-irradiance curves indicated the algae suffered reductions in both maximum rates of photosynthesis and saturation irradiances. However, all three species exhibited higher photosynthetic efficiencies under non-saturating irradiances (those below 30 _mol photons×m-2×s-1). In contrast, calcification rates under elevated pCO_ varied among the species, declining by 18% in B. californica and 49% in C. officinalis, but increasing by 20% in C. tuberculosum. Likewise, percent CaCO_ in the algal thalli decreased in B. californica and C. officinalis, but increased in C. tuberculosum under elevated pCO_, suggesting that B. californica and C. officinalis may be more strongly adversely impacted by climate change than C. tuberculosum. Assessing only the immediate responses to elevated CO_ neglects the possibility of phenotypic plasticity, which may result in variable abilities to acclimate to changing environmental conditions. To examine this in the three species of geniculate coralline algae, a longer four-week mesocosm ...
|
|---|