Alternative stable states of a kelp-bed ecosystem

我的研究计划的长期目标是：1）调查生物和物理过程，管理在加拿大东部的岩石潮下带生态系统，海带床和海胆贫瘠地的两个替代状态之间的大规模转变; 2）确定这些状态转变对生态系统功能和服务的后果;（3）开发群落结构和动态的预测模型，以帮助评估生态系统健康和自然资源管理。在我目前的研究中，经历周期性交替状态的浅水系统与深水中相邻组合之间的连通性已成为一个重要主题。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25米以上的深度，海胆的数量会大量减少。当海胆死亡后，海带和其他海藻在浅水区繁殖时，这些生活在深水区的海胆沿着浮出水面的海带床的下缘形成了觅食群（前沿）。这些锋面向海岸迁移，开始破坏性的放牧过程，最终恢复贫瘠的状态。有机物质和能量从浅海藻床流向深生境是另一种形式的连通性。海带的叶子不断地被侵蚀和破碎，或者在暴风雨中被移动。波浪和水流将这些漂流的碎片和颗粒物质输送到更深的水域，在那里它们成为海胆和其他消费者的食物来源。拟议的研究将解决几个关键的和相互关联的要素交替状态的动态，因为他们适用于新斯科舍省的海岸：1）引进的病原体，驱动过渡到海带床状态的机制; 2）潜在的积累抗病能力的海胆，这将提高贫瘠状态的恢复力; 3）在大规模死亡事件之后重新填充浅区的深生活海胆的分布和丰度; 4）海带碎片在支持这些深生活海胆的生长和繁殖方面的重要性;和5）捕捞海胆作为调节放牧强度的一种手段以维持转型国家之间的动态平衡的潜力。

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.