Species invasion and the ecology of rocky subtidal communities

作为研究海洋的生态学家和学生，我们越来越意识到，相对于自然进化的状态，人类的活动已经深刻地改变了沿海生态系统。最紧迫的问题之一是将新物种引入海洋生物群落，然后迅速扩大以取代本地物种。这些人为媒介的生物入侵可能导致生境和生态系统结构和功能的显著变化，往往会带来可怕的生态和经济后果。生活在加拿大大西洋多岩石海床上的海藻、无脊椎动物和鱼类群落是严重受影响的生态系统的一个显著例子。从历史上看，这个群落一直在两种生态状态之间交替，这两种状态依赖于一种关键的草食动物--海胆的丰度：海胆稀少的海带床和海胆占据主导地位、海藻稀少的荒地。这些状态之间的周期性交替是由一种导致海胆死亡的疾病的零星爆发推动的。在这种扰动和不稳定的背景下，最近引入的物种之间的协同作用使生态系统转向由一种入侵的亚洲海藻主导的新的群落状态。我们研究的目的是了解生物和环境过程，这些过程调节生态系统状态之间的转换或决定其持久性。特别是，我们将使用一系列实验和观察方法来研究入侵物种对生态系统结构和功能的影响，以检查物种之间的相互作用，构建食物网，并开发预测数学模型，这些模型是对这个日益扰动的生态系统进行智能管理所需的。

As ecologists and students of the ocean, we have become increasingly aware that coastal ecosystems have been profoundly altered, relative to their naturally evolved state, by the activity of humans. Among the most urgent concerns is the introduction of new species into marine communities, that then expand rapidly to replace native species. These human-mediated biological invasions can result in pronounced changes in habitat and ecosystem structure and function, often with dire ecologic and economic consequences. The community of seaweeds, invertebrates and fish that inhabit the rocky seabed of Atlantic Canada provides a striking example of a heavily impacted ecosystem. Historically, this community has alternated between two ecological states dependent on the abundance of a key herbivore, the sea urchin: kelp beds where urchins are rare and barrens where urchins dominate the seascape and seaweeds are absent. Cyclical alternations between these states are driven by sporadic outbreaks of a disease that kills urchins. Amid this backdrop of perturbation and instability, synergistic interactions between recently introduced species have shifted the ecosystem towards a novel community state dominated by an invasive Asian seaweed. The objective of our research is to understand the biological and environmental processes that regulate transitions between ecosystem states or determine their persistence. In particular, we will investigate the effects of invasive species on ecosystem structure and function using a range of experimental and observational approaches to examine species interactions, construct food webs, and develop predictive mathematical models that are needed for intelligent management of this increasingly perturbed ecosystem.