Coastal and Marine Research Centre, Australian Rivers Institute, School of Environment and Science, Griffith University, Gold Coast, QLD 4222, Australia.
Coastal and Marine Research Centre, Australian Rivers Institute, School of Environment and Science, Griffith University, Gold Coast, QLD 4222, Australia.
Sci Total Environ. 2023 Nov 20;900:165865. doi: 10.1016/j.scitotenv.2023.165865. Epub 2023 Jul 27.
Ecosystems are increasingly affected by multiple anthropogenic stressors that contribute to habitat degradation and loss. Natural ecosystems are highly dynamic, yet multiple stressor experiments often ignore variability in stressor intensity and do not consider how effects could be mediated across trophic levels, with implications for models that underpin stressor management. Here, we investigated the in situ effects of changes in stressor intensity (i.e., fluctuations) and synchronicity (i.e., timing of fluctuations) on a seagrass community, applying the stressors reduced light and physical disturbance to the sediment. We used structural equation models (SEMs) to identify causal effects of dynamic multiple stressors on seagrass shoot density and leaf surface area, and abundance of associated crustaceans. Responses depended on whether stressor intensities fluctuated or remained static. Relative to static stressor exposure at the end of the experiment, shoot density, leaf surface area, and crustacean abundance all declined under in-phase (synchronous; 17, 33, and 30 % less, respectively) and out-of-phase (asynchronous; 11, 28, and 39 % less, respectively) fluctuating treatments. Static treatment increased seagrass leaf surface area and crustacean abundance relative to the control group. We hypothesised that crustacean responses are mediated by changes in seagrass; however, causal analysis found only weak evidence for a mediation effect via leaf surface area. Changes in crustacean abundance, therefore, were primarily a direct response to stressors. Our results suggest that the mechanisms underpinning stress responses change when stressors fluctuate. For instance, increased leaf surface area under static stress could be caused by seagrass acclimating to low light, whereas no response under fluctuating stressors suggests an acclimation response was not triggered. The SEMs also revealed that community responses to the stressors can be independent of one another. Therefore, models based on static experiments may be representing ecological mechanisms not observed in natural ecosystems, and underestimating the impacts of stressors on ecosystems.
生态系统越来越受到多种人为胁迫的影响，这些胁迫导致栖息地退化和丧失。自然生态系统具有高度的动态性，但多胁迫实验往往忽略了胁迫强度的可变性，也没有考虑到这些效应如何在营养级之间进行调节，这对支持胁迫管理的模型产生了影响。在这里，我们研究了胁迫强度（即波动）和同步性（即波动的时间）变化对海草群落的原位影响，将减少光照和物理干扰这两种胁迫施加到沉积物中。我们使用结构方程模型（SEM）来确定动态多胁迫对海草芽密度和叶片表面积以及相关甲壳类动物丰度的因果影响。这些响应取决于胁迫强度是波动还是保持静态。与实验结束时静态胁迫暴露相比，在同相（同步）和异相（异步）波动处理下，芽密度、叶片表面积和甲壳类动物丰度分别下降了 17%、33%和 30%，以及 11%、28%和 39%。与对照组相比，静态处理增加了海草叶片表面积和甲壳类动物丰度。我们假设甲壳类动物的反应是由海草的变化介导的；然而，因果分析只发现了通过叶片表面积进行介导的微弱证据。因此，甲壳类动物丰度的变化主要是对胁迫的直接反应。我们的结果表明，当胁迫波动时，应激反应的机制会发生变化。例如，在静态胁迫下增加的叶片表面积可能是由海草对低光照的适应引起的，而在波动胁迫下没有反应表明没有触发适应反应。SEM 还表明，群落对胁迫的反应彼此独立。因此，基于静态实验的模型可能无法反映自然生态系统中观察到的生态机制，并低估了胁迫对生态系统的影响。
