From the predictable to the unexpected: kelp forest and benthic invertebrate community dynamics following decades of sea otter expansion
From the predictable to the unexpected: kelp forest and benthic invertebrate community dynamics following decades of sea otter expansion
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从可预测到意外：数十年海獭扩张后的海带森林和底栖无脊椎动物群落动态
作者：
A. Shelton;C. Harvey;J. Samhouri;Kelly S. Andrews;B. E. Feist;K. Frick;N. Tolimieri;Gregory D. Williams;L. Antrim;H. Berry
捕食者的恢复有可能恢复生态系统并从根本上改变它们提供的服务。一个标志性的例子是东北太平洋海獭的主要捕食行为。在这里，我们结合了美国华盛顿州海獭丰度、冠层海带面积和底栖无脊椎动物丰度的空间时间序列，以研究海獭重新引入对海带和海带森林群落的变化影响。我们利用海獭恢复的空间变化来了解海獭和海带森林群落之间的联系。海獭的增加导致海獭猎物（尤其是吃海带的海胆）显着减少，并导致冠层海带从 1980 年代末到 2000 年左右扩张。然而，虽然海獭和海带种群增长率在 2002 年之前呈正相关，但这种关联在过去二十年中消失了。尽管调查显示海獭的猎物数量持续减少，但这种脱节还是发生了。海带面积趋势与当前密度下的海獭和底栖无脊椎动物丰度脱钩。最近 15 年，海带丰度的变异性有所下降，因为不同地点的海带丰度具有同步性。总之，这些发现表明，近岸群落对海獭种群扩张的最初反应符合营养级联理论，但现在，其他因素在影响群落动态方面可能同样重要或更重要。因此，必须在复杂多变的环境条件背景下考虑海獭捕食在生态系统恢复中的效用。
The recovery of predators has the potential to restore ecosystems and fundamentally alter the services they provide. One iconic example of this is keystone predation by sea otters in the Northeast Pacific. Here, we combine spatial time series of sea otter abundance, canopy kelp area, and benthic invertebrate abundance from Washington State, USA, to examine the shifting consequences of sea otter reintroduction for kelp and kelp forest communities. We leverage the spatial variation in sea otter recovery to understand connections between sea otters and the kelp forest community. Sea otter increases created a pronounced decline in sea otter prey—particularly kelp-grazing sea urchins—and led to an expansion of canopy kelps from the late 1980s until roughly 2000. However, while sea otter and kelp population growth rates were positively correlated prior to 2002, this association disappeared over the last two decades. This disconnect occurred despite surveys showing that sea otter prey have continued to decline. Kelp area trends are decoupled from both sea otter and benthic invertebrate abundance at current densities. Variability in kelp abundance has declined in the most recent 15 years, as it has the synchrony in kelp abundance among sites. Together, these findings suggest that initial nearshore community responses to sea otter population expansion follow predictably from trophic cascade theory, but now, other factors may be as or more important in influencing community dynamics. Thus, the utility of sea otter predation in ecosystem restoration must be considered within the context of complex and shifting environmental conditions.