Departament of Ecology and Marine Resources, IMEDEA (CSIC-UIB), Esporles, Spain.
Department of Organic Chemistry, University of Cadiz, Cadiz, Spain.
Glob Chang Biol. 2017 Nov;23(11):4530-4543. doi: 10.1111/gcb.13768. Epub 2017 Jun 26.
Increases in seawater temperature are expected to have negative consequences for marine organisms. Beyond individual effects, species-specific differences in thermal tolerance are predicted to modify species interactions and increase the strength of top-down effects, particularly in plant-herbivore interactions. Shifts in trophic interactions will be especially important when affecting habitat-forming species such as seagrasses, as the consequences on their abundance will cascade throughout the food web. Seagrasses are a major component of coastal ecosystems offering important ecosystem services, but are threatened by multiple anthropogenic stressors, including warming. The mechanistic understanding of seagrass responses to warming at multiple scales of organization remains largely unexplored, especially in early-life stages such as seedlings. Yet, these early-life stages are critical for seagrass expansion processes and adaptation to climate change. In this study, we determined the effects of a 3 month experimental exposure to present and predicted mean summer SST of the Mediterranean Sea (25°C, 27°C, and 29°C) on the photophysiology, size, and ecology (i.e., plant-herbivore interactions) of seedlings of the seagrass Posidonia oceanica. Warming resulted in increased mortality, leaf necrosis, and respiration as well as lower carbohydrate reserves in the seed, the main storage organ in seedlings. Aboveground biomass and root growth were also limited with warming, which could hamper seedling establishment success. Furthermore, warming increased the susceptibility to consumption by grazers, likely due to lower leaf fiber content and thickness. Our results indicate that warming will negatively affect seagrass seedlings through multiple direct and indirect pathways: increased stress, reduced establishment potential, lower storage of carbohydrate reserves, and increased susceptibly to consumption. This work provides a significant step forward in understanding the major mechanisms that will drive the capacity of seagrass seedlings to adapt and survive to warming, highlighting the potential additive effects that herbivory will have on ultimately determining seedling success.
预计海水温度升高将对海洋生物产生负面影响。除了个体影响外，物种间热耐受性的差异预计会改变物种间的相互作用，并增加自上而下的影响的强度，尤其是在植物-食草动物的相互作用中。当影响到海草等形成栖息地的物种时，营养级联的变化将尤为重要，因为它们的丰度变化将在整个食物网中产生级联效应。海草是沿海生态系统的主要组成部分，提供了重要的生态系统服务，但受到多种人为胁迫的威胁，包括变暖。在多个组织层次上，海草对变暖的机制理解在很大程度上仍未得到探索，特别是在幼苗等早期生命阶段。然而，这些早期生命阶段对于海草的扩张过程和适应气候变化至关重要。在这项研究中，我们确定了 3 个月的实验暴露于地中海目前和预测的夏季平均海表温度（25°C、27°C 和 29°C）对海草波西多尼亚海洋床幼苗的光生理、大小和生态（即植物-食草动物相互作用）的影响。变暖导致死亡率、叶片坏死和呼吸增加，以及种子中碳水化合物储备减少，种子是幼苗的主要储存器官。随着变暖，地上生物量和根生长也受到限制，这可能会阻碍幼苗的建立成功率。此外，变暖增加了食草动物的易感性，可能是由于叶片纤维含量和厚度降低。我们的研究结果表明，变暖将通过多种直接和间接途径对海草幼苗产生负面影响：增加压力、降低建立潜力、减少碳水化合物储备、以及增加易感性。这项工作为理解将推动海草幼苗适应和生存变暖的主要机制提供了重要的一步，突出了食草动物将对最终确定幼苗成功的潜在附加影响。
