RAPID: Testing the rocky intertidal community consequences of the decimation of purple sea star populations along the Oregon coast by sea star wasting disease

本研究将调查俄勒冈州海岸沿着的消耗性疾病对海星星种群的毁灭性生态后果。 消耗性疾病的特征是在海星星上形成溃疡，进展导致手臂丧失，最终导致动物死亡。 早在2013年4月，在不列颠哥伦比亚省、华盛顿和加州的海星星种群中就报告了消耗性疾病，包括紫海星星，Pisaster ochraceus。 在俄勒冈州，2014年4月首次观察到消瘦，到2014年6月，感染率高达80%，海星星星丰度下降。 按照这个速度，到2014年夏末，许多种群可能会消失。 先前的研究表明，在没有紫海星星的情况下，中海岸贻贝种群增加，最终导致海岸低的海藻和无脊椎动物过度生长，减少了生物多样性。 然而，由于这种规模的疾病事件从未在整个海岸线沿着发生过，目前还不清楚之前观察到的贻贝小规模扩张是否会是这一事件的普遍结果。 一种可能性是，不受消耗影响的捕食者，如海螺和螃蟹，将增加它们的捕食效果，并削弱预期的贻贝入侵低海岸。 该项目的研究将通过测试这些替代掠食者的作用来评估这种可能性。 更广泛的影响包括本科生和研究生的培训，沿海居民的参与和微纪录片和视频的制作，以记录这一生态系统不断变化的背景。 首先，在没有Pisaster ochraceus的情况下，海螺的捕食将通过增加海螺丰度和海螺大小来增加强度，并至少部分补偿Pisaster的缺失。 二是小海星星藻Leptasterias spp.也将扩大其作为捕食者的作用，通过增加规模和丰富性，并扩大其栖息地以外的贻贝床。 虽然这种海洋星星的个体也被观察到患有消瘦症，但到目前为止频率似乎很低，而且这种物种可能会持续下去。第三，通常主要是潮下带物种的巨蟹座，将扩大其范围到潮间带，并有助于弥补Pisaster的损失。 这些假设的检验将包括手动去除实验（去除青春痘、去除细粉虫、去除两者或两者都不去除）、笼排除实验（青春痘排除）、笼包含-排除实验（包含细粉虫、排除细粉虫）。 实验将在适当的控制下重复进行，并在俄勒冈州中部海岸的多个地点进行，这些地点在人口丰度、猎物和捕食者招募率以及海洋条件方面自然变化。 在这种前所未有的情况下获得的结果将加深和扩大我们的经验理解的动态的一个标志性的生态系统，并将有助于参数化社区模型。

This study will investigate the ecological consequences of the decimation of sea star populations by wasting disease along the Oregon coast. Hallmarks of wasting disease are the formation of sores on the sea star that progress to cause loss of arms, and ultimately death of the animal. Wasting disease was reported in sea star populations including those of the purple sea star, Pisaster ochraceus, in British Columbia, Washington, and California as early as April 2013. In Oregon, wasting was first observed in April 2014, and by June 2014 rates of infection ranged up to 80%, and sea star abundance had declined. At that rate, many populations may disappear by the end of summer 2014. Prior research has shown that in the absence of the purple sea star, mid-shore mussel populations increase, and ultimately overgrow the sea weeds and invertebrates that occur low on the shore, reducing biodiversity. However, because disease events of this magnitude have never occurred along the entire coastline, it is unclear if the small-scale expansion of mussels observed previously will be a general result of this event. One possibility is that predators unaffected by wasting, such as whelks and crabs, will increase their predation effects and blunt the expected invasion of mussels to the low shore. The research in this project will evaluate this possibility by testing the role of these alternative predators. Broader Impacts include the training of undergraduate and graduate students, the involvement of coastal residents and the production of microdocumentaries and video to document the changing context of this ecosystem.The research project is designed to test three hypotheses. First, that in the absence of Pisaster ochraceus, predation by whelks will increase in strength through increases in whelk abundance and in whelk size, and at least partially compensate for the absence of Pisaster. Second, the small sea star Leptasterias spp. will also expand its role as a predator through increased size and abundance, and expansion of its habitat beyond mussel beds. Although individuals of this sea star have been observed to suffer from wasting as well, the frequency so far appears low, and it seems likely this species may persist. Third, the crab Cancer productus, normally mostly a subtidal species, will expand its range into the intertidal and help to compensate for the loss of Pisaster. Tests of these hypotheses will include manual removal experiments (whelk removal, Leptasterias removal, removal of both and of neither), cage exclusion experiments (whelk exclusions), cage inclusion-exclusion experiments (Leptasterias inclusion, Leptasterias exclusion). Experiments will be replicated with appropriate controls, and done at multiple sites on the central Oregon coast that vary naturally in population abundances, rates of prey and predator recruitment, and oceanographic conditions. Results obtained under this unprecedented set of circumstances will deepen and expand our empirical understanding of the dynamics of an iconic ecosystem, and will help parameterize community models.