Alternative stable states of a kelp-bed ecosystem

我的研究计划的长期目标是：1)调查在加拿大东部，海带床和海胆贫瘠的岩石潮下生态系统的两种可选状态之间进行大规模转变的生物和物理过程；2)确定这些状态变化对生态系统功能和服务的影响；3)建立有助于生态系统健康评估和自然资源管理的群落结构和动态预测模型。在状态上经历周期性交替的浅层系统与深水中的相邻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（主要的食草动物）提供了一个热避难所，防止一种疾病在25米以上的深度杀死它们的种群。当海胆死亡后，海带和其他海藻重新在浅水区定居，这些生活在深海的海胆沿着新出现的海带床的下边缘形成觅食聚集（前沿）。这些锋面向海岸迁移，开始了破坏性放牧的过程，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更深的栖息地是另一种形式的连通性。海带叶子不断地被侵蚀和破碎，或者在风暴中被移走。波浪和水流将这些漂浮的碎片和颗粒物质带到更深的水域，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要素，因为它们适用于新斯科舍省的海岸：1)引入病原体的机制，驱动过渡到海带床状态；2)海胆积累抗病能力的潜力，可增强对荒漠状态的适应能力；3)深海海胆的分布和丰度，在大规模死亡事件发生后重新在浅水区繁殖；4)海带碎屑对支持这些深海海胆生长和繁殖的重要性；5)海胆收获作为调节放牧强度以维持过渡状态之间动态平衡的手段的潜力。

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.