Department of Biological and Environmental Sciences, University of Gothenburg, 405 30 Göteborg, Sweden.
Proc Natl Acad Sci U S A. 2013 May 21;110(21):8603-8. doi: 10.1073/pnas.1303797110. Epub 2013 Apr 29.
It is well known that ocean acidification can have profound impacts on marine organisms. However, we know little about the direct and indirect effects of ocean acidification and also how these effects interact with other features of environmental change such as warming and declining consumer pressure. In this study, we tested whether the presence of consumers (invertebrate mesograzers) influenced the interactive effects of ocean acidification and warming on benthic microalgae in a seagrass community mesocosm experiment. Net effects of acidification and warming on benthic microalgal biomass and production, as assessed by analysis of variance, were relatively weak regardless of grazer presence. However, partitioning these net effects into direct and indirect effects using structural equation modeling revealed several strong relationships. In the absence of grazers, benthic microalgae were negatively and indirectly affected by sediment-associated microalgal grazers and macroalgal shading, but directly and positively affected by acidification and warming. Combining indirect and direct effects yielded no or weak net effects. In the presence of grazers, almost all direct and indirect climate effects were nonsignificant. Our analyses highlight that (i) indirect effects of climate change may be at least as strong as direct effects, (ii) grazers are crucial in mediating these effects, and (iii) effects of ocean acidification may be apparent only through indirect effects and in combination with other variables (e.g., warming). These findings highlight the importance of experimental designs and statistical analyses that allow us to separate and quantify the direct and indirect effects of multiple climate variables on natural communities.
众所周知，海洋酸化会对海洋生物产生深远的影响。然而，我们对海洋酸化的直接和间接影响知之甚少，也不知道这些影响如何与其他环境变化特征（如变暖、消费者压力下降）相互作用。在这项研究中，我们测试了消费者（无脊椎中型食草动物）的存在是否会影响酸化和变暖对海草草甸中底栖微藻的相互作用。方差分析评估的酸化和变暖对底栖微藻生物量和生产力的净效应相对较弱，无论是否存在食草动物。然而，使用结构方程模型将这些净效应划分为直接和间接效应，揭示了一些强烈的关系。在没有食草动物的情况下，底栖微藻受到与沉积物相关的微藻食草动物和大型藻类遮荫的负面影响，而间接和直接受到酸化和变暖的正面影响。综合间接和直接效应，没有或几乎没有净效应。在有食草动物的情况下，几乎所有的直接和间接气候效应都不显著。我们的分析强调了（i）气候变化的间接效应可能至少与直接效应一样强烈，（ii）食草动物在介导这些效应中至关重要，以及（iii）海洋酸化的影响可能只有通过间接效应和与其他变量（如变暖）相结合才能显现出来。这些发现强调了实验设计和统计分析的重要性，这些设计和分析可以使我们分离和量化多种气候变量对自然群落的直接和间接影响。
