Lee Juhyung, Hughes Brent B, Kroeker Kristy J, Owens Ava, Wong Candace, Micheli Fiorenza
Hopkins Marine Station of Stanford University, 120 Ocean View Blvd, Pacific Grove, CA 93950, USA.
Nicholas School of the Environment, Duke University, Beaufort, NC 28516, USA.
Sci Total Environ. 2022 Feb 20;808:151594. doi: 10.1016/j.scitotenv.2021.151594. Epub 2021 Nov 24.
Global stressors are increasingly altering ecosystem resistance, resilience, and functioning by reorganizing vital species interactions. However, our predictive understanding of these changes is hindered by failures to consider species-specific functional roles and stress responses within communities. Stressor-driven loss or reduced performance of strongly interacting species may generate abrupt shifts in ecosystem states and functions. Yet, empirical support for this prediction is scarce, especially in marine climate change research. Using a marine assemblage comprising a habitat-forming seagrass (Phyllospadix torreyi), its algal competitor, and three consumer species (algal grazers) with potentially different functional roles and pH tolerance, we investigated how ocean acidification (OA) may, directly and indirectly, alter community resistance. In the field and laboratory, hermit crabs (Pagurus granosimanus and P. hirsutiusculus) and snails (Tegula funebralis) displayed distinct microhabitat use, with hermit crabs more frequently grazing in the area of high algal colonization (i.e., surfgrass canopy). In mesocosms, this behavioral difference led to hermit crabs exerting ~2 times greater per capita impact on algal epiphyte biomass than snails. Exposure to OA variably affected the grazers: snails showed reduced feeding and growth under extreme pH (7.3 and 7.5), whereas hermit crabs (P. granosimanus) maintained a similar grazing rate under all pH levels (pH 7.3, 7.5, 7.7, and 7.95). Epiphyte biomass increased more rapidly under extreme OA (pH 7.3 and 7.5), but natural densities of snails and hermit crabs prevented algal overgrowth irrespective of pH treatments. Finally, grazers and acidification additively increased surfgrass productivity and delayed the shoot senescence. Hence, although OA impaired the function of the most abundant consumers (snails), strongly interacting and pH-tolerant species (hermit crabs) largely maintained the top-down pressure to facilitate seagrass dominance. Our study highlights significant within-community variation in species functional and response traits and shows that this variation has important ecosystem consequences under anthropogenic stressors.
全球压力源正通过重组重要的物种间相互作用，日益改变生态系统的抵抗力、恢复力和功能。然而，由于未能考虑群落内物种特定的功能作用和应激反应，我们对这些变化的预测性理解受到了阻碍。压力源驱动的强相互作用物种的损失或性能下降，可能会导致生态系统状态和功能的突然转变。然而，这一预测的实证支持很少，尤其是在海洋气候变化研究中。我们使用了一个海洋群落，其中包括一种形成栖息地的海草（托氏叶垫藻）、其藻类竞争者，以及三种具有潜在不同功能作用和耐pH值能力的消费者物种（藻类食草动物），来研究海洋酸化（OA）如何直接和间接地改变群落抵抗力。在野外和实验室中，寄居蟹（颗粒寄居蟹和多毛寄居蟹）和蜗牛（黑凹螺）表现出不同的微生境利用方式，寄居蟹更频繁地在高藻类定殖区域（即浪草冠层）觅食。在中宇宙实验中，这种行为差异导致寄居蟹对藻类附生生物量的人均影响比蜗牛大2倍左右。暴露于海洋酸化环境对食草动物产生了不同影响：在极端pH值（7.3和7.5）下，蜗牛的摄食和生长减少，而寄居蟹（颗粒寄居蟹）在所有pH值水平（pH 7.3、7.5、7.7和7.95）下保持相似的觅食率。在极端海洋酸化（pH 7.3和7.5）下，附生生物量增加得更快，但蜗牛和寄居蟹的自然密度阻止了藻类的过度生长，无论pH处理如何。最后，食草动物和酸化共同增加了浪草的生产力，并延迟了草茎衰老。因此，尽管海洋酸化损害了最丰富的消费者（蜗牛）的功能，但强相互作用且耐pH值的物种（寄居蟹）在很大程度上维持了自上而下的压力，以促进海草的优势地位。我们的研究强调了群落内物种功能和反应特征的显著差异，并表明这种差异在人为压力源下具有重要的生态系统后果。
