Collaborative Research: RAPID: Nearshore settlement and hydrodynamics in Southern California during El Nino, and the transition to normal ocean conditions: boom and bust?

了解幼虫如何在沿海海洋中运输是表征海洋生物种群波动的关键。研究表明，栖息在浅水中的物种的幼虫可以通过垂直移动到洋流中来对不断变化的海洋条件做出行为反应，这可以促进它们迁移到沿海、近岸栖息地，在那里它们定居到底部栖息地并完成其生命周期。然而，促进这种运输的海洋学机制，以及它们如何受到厄尔尼诺等罕见事件的影响，目前还没有得到很好的解决。鉴于气候变化下厄尔尼诺事件的发生频率和强度可能会增加，因此有必要评估厄尔尼诺现象如何影响幼虫运输和幼虫定居。为此，本研究将使用一套前所未有的近岸生物和物理测量数据，涵盖厄尔尼诺现象发生前、厄尔尼诺现象期间，以及预测的厄尔尼诺中性条件的回归，以机械方式测试近岸沿海环境中幼虫运输和定居的反应。该项目还将为文科大学圣地亚哥大学的学生提供教育和研究机会。将为本科生开发至少一项展示厄尔尼诺现象对幼虫运输和定居影响的实验室练习，并将招募学生参与该项目的各个方面，为他们提供实践研究经验。这项研究将构成至少一名硕士学位论文工作的基础。研究生。最后，鉴于该研究属于海洋保护区，结果将广泛传播并与沿海管理者和加利福尼亚州鱼类和野生动物部共享。幼体运输和定居是了解底栖无脊椎动物种群动态的基本过程。先前的研究和未发表的观察结果表明，厄尔尼诺事件深刻影响了社区和种群过程，在南加州，厄尔尼诺现象的影响范围从改变幼虫运输和当地种群的定居，到亚热带物种的地理扩张。这项研究将检验当前（2015-2016）厄尔尼诺事件将导致南加州近岸栖息地藤壶幼虫运输和定居减少的假设。可能涉及两种机制：首先，厄尔尼诺现象迫使温跃层加深，会导致内潮汐幼虫运输减少，而这种机制需要使温跃层变浅。其次，与厄尔尼诺中性条件相比，在厄尔尼诺现象期间，滨海藤壶幼虫的分布更深、更近海，对近岸栖息地的限制也更少，导致近岸幼虫丰度和定居减少。厄尔尼诺现象对南加州伯德罗克近岸环流、水文学、幼虫运输和定居的影响将通过以下方式测量：a) 部署一系列仪器来测量温度、压力（波浪）和洋流； b) 测量藤壶幼虫的每日沉降量； c) 评估无脊椎动物幼虫的跨岸和深度分布。这些观测结果将与 2014 年（厄尔尼诺中性条件）和 2015 年（厄尔尼诺现象期间）在伯德罗克进行的两年可比观测结果进行对比。此外，调查人员还将每周测量 Bird Rock 和以北 7 公里处的 Dike Rock 的沉积情况，之前在 1997/1998 年厄尔尼诺现象结束时的观测表明，藤壶沉积量非常高。这将能够评估厄尔尼诺现象消失时沉降反应的普遍性，并检查沉降沿海岸线的变化情况。

Understanding how larvae are transported in the coastal ocean is key for characterizing the population fluctuations of marine organisms. Studies demonstrate that larvae of species that inhabit shallow waters can behaviorally respond to changing oceanographic conditions by moving vertically into currents that can promote their transport to coastal, nearshore habitats where they settle to bottom habitats and complete their life cycle. However, the oceanographic mechanisms that promote such transport, and how they might be impacted by infrequent events such as El Niño, are poorly resolved. Given that El Niño events might increase in frequency and magnitude under climate change, it is imperative to assess how El Niño affects larval transport and larval settlement. To this end, this study will use an unprecedented set of nearshore biological and physical measurements spanning pre-El-Niño, during El Niño, and the predicted return to El Niño neutral conditions, to test mechanistically how larval transport and settlement respond in a nearshore coastal environment. This project will also provide educational and research opportunities for students at the University of San Diego, a liberal arts university. At least one laboratory exercise demonstrating the impacts of El Niño on larval transport and settlement will be developed for undergraduate students, and students will be recruited to participate in all aspects of the project to provide them with hands-on research experience. This research will form the basis for the thesis work of at least one M.S. graduate student. Finally, given that the research falls within a Marine Protected Area, results will be broadly disseminated and shared with coastal managers and the CA Department of Fish and Wildlife.Larval transport and settlement are fundamental processes for understanding the population dynamics of benthic invertebrates. Previous studies and unpublished observations indicate that El Niño events profoundly impact community and population processes, and in Southern California, El Niño effects range from alteration of larval transport and settlement of local populations, to the geographic expansion of subtropical species. This research will test the hypothesis that the current (2015-2016) El Niño event will result in a reduction of barnacle larval transport and settlement in Southern California nearshore habitats. Two mechanisms might be involved; first, a deepening of the thermocline forced by El Niño would result in reduction of larval transport by internal tidal bores, a mechanism that requires shallowing of the thermocline. Second, the distribution of larvae of littoral barnacles would be deeper, more offshore, and less constrained to nearshore habitats during El Niño than in El Niño neutral conditions, resulting in a reduction of nearshore larval abundance and settlement. The effects of El Niño on nearshore circulation, hydrography, larval transport and settlement in Bird Rock, Southern California, will be measured by a) deploying an array of instrumentation to measure temperature, pressure (waves) and currents; b) measuring daily barnacle larval settlement, and; c) assessing cross-shore and depth distribution of invertebrate larvae. These observations will be contrasted with two years of comparable observations taken at Bird Rock in 2014 (El Niño neutral conditions) and 2015 (during El Niño). Additionally, the investigators will measure weekly settlement at Bird Rock, and at Dike Rock, a site 7 km to the north, where previous observations at the end of the 1997/1998 El Niño indicated that barnacle settlement was very high. This will enable the evaluation of the generality of the settlement response as El Niño conditions eclipse, and examination of how settlement varies along a coastline.