Hamilton Sara L, Bell Tom W, Watson James R, Grorud-Colvert Kirsten A, Menge Bruce A
Department of Integrative Biology, Oregon State University, Corvallis, Oregon, 97331, USA.
Earth Research Institute, University of California, Santa Barbara, California, 93106, USA.
Ecology. 2020 Jul;101(7):e03031. doi: 10.1002/ecy.3031. Epub 2020 Apr 17.
A critical tool in assessing ecosystem change is the analysis of long-term data sets, yet such information is generally sparse and often unavailable for many habitats. Kelp forests are an example of rapidly changing ecosystems that are in most cases data poor. Because kelp forests are highly dynamic and have high intrinsic interannual variability, understanding how regional-scale drivers are driving kelp populations-and particularly how kelp populations are responding to climate change-requires long-term data sets. However, much of the work on kelp responses to climate change has focused on just a few, relatively long-lived, perennial, canopy-forming species. To understand how kelp populations with different life history traits are responding to climate-related variability, we leverage 35 yr of Landsat satellite imagery to track the population size of an annual, ruderal kelp, Nereocystis luetkeana, across Oregon. We found high levels of interannual variability in Nereocystis canopy area and varying population trajectories over the last 35 yr. Surprisingly, Oregon Nereocystis population sizes were unresponsive to a 2014 marine heat wave accompanied by increases in urchin densities that decimated northern California Nereocystis populations. Some Oregon Nereocystis populations have even increased in area relative to pre-2014 levels. Analysis of environmental drivers found that Nereocystis population size was negatively correlated with estimated nitrate levels and positively correlated with winter wave height. This pattern is the inverse of the predicted relationship based on extensive prior work on the perennial kelp Macrocystis pyrifera and may be related to the annual life cycle of Nereocystis. This article demonstrates (1) the value of novel remote sensing tools to create long-term data sets that may challenge our understanding of nearshore marine species and (2) the need to incorporate life history traits into our theory of how climate change will shape the ocean of the future.
评估生态系统变化的一个关键工具是对长期数据集进行分析，然而这类信息通常很稀少，而且在许多栖息地往往无法获取。海带林就是快速变化的生态系统的一个例子，在大多数情况下，关于海带林的数据很匮乏。由于海带林具有高度动态性且年际变化很大，了解区域尺度的驱动因素如何影响海带种群，尤其是海带种群如何应对气候变化，需要长期数据集。然而，许多关于海带对气候变化响应的研究仅聚焦于少数几种寿命相对较长、多年生、形成冠层的物种。为了了解具有不同生活史特征的海带种群如何应对与气候相关的变化，我们利用35年的陆地卫星图像来追踪一种一年生、杂草性海带——鲁氏巨藻在俄勒冈州的种群规模。我们发现鲁氏巨藻冠层面积的年际变化很大，且在过去35年里种群轨迹各不相同。令人惊讶的是，俄勒冈州的鲁氏巨藻种群规模对2014年的一次海洋热浪没有反应，尽管此次热浪伴随着海胆密度的增加，而海胆密度的增加使北加利福尼亚州的鲁氏巨藻种群数量大幅减少。与2014年之前的水平相比，俄勒冈州的一些鲁氏巨藻种群面积甚至有所增加。对环境驱动因素的分析发现，鲁氏巨藻种群规模与估计的硝酸盐水平呈负相关，与冬季波高呈正相关。这种模式与基于对多年生海带巨藻的大量先前研究预测的关系相反，可能与鲁氏巨藻的一年生生命周期有关。本文证明了：（1）新型遥感工具对于创建长期数据集的价值，这些数据集可能会挑战我们对近岸海洋物种的理解；（2）需要将生活史特征纳入我们关于气候变化将如何塑造未来海洋的理论中。
