Alternative stable states of a kelp-bed ecosystem

我的研究计划的长期目标是：1)调查控制加拿大东部岩石潮下生态系统两种不同状态--海藻床和海胆荒地--之间大规模转变的生物和物理过程；2)确定这些状态转变对生态系统功能和服务的影响；以及3)开发群落结构和动态的预测模型，帮助评估生态系统健康和自然资源管理。浅水系统在状态上经历周期性变化，与深水中相邻的组合之间的连通性已成为我目前研究的一个重要主题。较深的栖息地为海胆提供了一个热避难所，海胆是主要的食草动物，在超过25米的深处，这种疾病会使它们的种群大量死亡。随着海藻和其他海藻在海胆死亡后重新定居在浅水区，这些生活在深海的海胆沿着刚出现的海藻床的下缘形成觅食聚集体(前缘)。这些锋面迁徙到岸边，开始了破坏性的放牧过程，最终恢复了贫瘠的状态。有机物质和能量从浅层海藻床流向较深的栖息地是另一种连接形式。海带叶子不断地侵蚀和破碎，或者在暴风雨中被赶走。海浪和洋流将这些漂浮的碎片和颗粒物输送到更深的水域，在那里它成为海胆和其他消费者的食物来源。拟议的研究将解决替代状态动力学的几个关键和相互关联的因素，因为它们适用于新斯科舍省海岸：1)病原体引入的机制，推动向海带床状态的转变；2)海胆积累抗病的潜力，这将增强贫瘠状态的弹性；3)在大规模死亡事件后重新出现在浅水区的深海海胆的分布和丰富；4)海带碎片对支持这些深海海胆的生长和繁殖的重要性；5)捕捞海胆作为调节放牧强度以维持过渡状态之间动态平衡的一种手段的潜力。

The long-term goals of my research program are: 1) to investigate biological and physical processes that govern large-scale shifts between two alternative states of the rocky subtidal ecosystem in eastern Canada, kelp beds and sea urchin barrens; 2) to determine the consequences of these state-shifts on ecosystem function and services; and 3) to develop predictive models of community structure and dynamics that aid in assessment of ecosystem health and management of natural resources. Connectivity between the shallow system, which undergoes cyclical alternations in state, and adjacent assemblages in deeper water has emerged as an important theme in my current research. Deeper habitats provide a thermal refuge for sea urchins, the dominant grazers, from a disease that decimates their populations at depths above 25 m. As kelps and other seaweeds recolonize the shallow zone after an urchin die-off, these deep-living sea urchins form feeding aggregations (fronts) along the lower margin of emergent kelp beds. These fronts migrate shoreward to begin a process of destructive grazing that ultimately reinstates the barrens state. The flow of organic matter and energy from shallow seaweed beds to deeper habitats is another form of connectivity. Kelp fronds continuously erode and fragment, or are dislodged during storms. Waves and currents convey these drifting fragments and particulate matter to deeper water, where it serves as food source for sea urchins and other consumers. The proposed research will address several critical and interconnected elements of alternative-state dynamics, as they apply to the coast of Nova Scotia: 1) the mechanism of introduction of the pathogen that drives the transition to the kelp-bed state; 2) the potential for accumulated disease resistance in sea urchins, which would enhance the resilience of the barrens state; 3) the distribution and abundance of deep-living sea urchins that repopulate the shallow zone after mass mortality events; 4) the importance of kelp debris in supporting growth and reproduction of these deep-living sea urchins; and 5) the potential of sea urchin harvesting as a means of regulating grazing intensity to maintain a dynamic balance between states in transition.