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

了解幼虫是如何在沿海海洋中运输的，是描述海洋生物种群波动的关键。研究表明，生活在浅海的物种幼虫可以通过垂直进入洋流来对不断变化的海洋条件做出反应，这可以促进它们向沿海和近岸生境迁移，在那里它们定居到海底生境并完成它们的生命周期。然而，促进这种迁移的海洋学机制，以及它们可能如何受到厄尔尼诺等罕见事件的影响，并没有得到很好的解决。鉴于厄尔尼诺现象在气候变化下可能增加发生的频率和程度，必须评估厄尔尼诺现象如何影响幼虫的运输和幼虫的定居。为此，这项研究将使用一套史无前例的、跨越厄尔尼诺现象之前、厄尔尼诺期间的近岸生物和物理测量，以及预计返回厄尔尼诺中性条件，从机械上测试幼虫在近岸沿海环境中的运输和定居反应。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。将为本科生开展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所有方面，为他们提供实践研究经验。这项研究将为至少一名硕士研究生的论文工作奠定基础。最后，鉴于研究属于海洋保护区，研究结果将被广泛传播，并与海岸管理者和加州鱼类和野生动物部分享。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。以前的研究和未发表的观察结果表明，厄尔尼诺事件对社区和人口进程产生了深远的影响，在南加州，厄尔尼诺效应的范围从改变幼虫的运输和当地人口的定居，到亚热带物种的地理扩张。这项研究将检验目前(2015-2016)厄尔尼诺事件将导致藤壶幼虫在南加州近岸栖息地的运输和定居减少的假设。这可能涉及两个机制：第一，厄尔尼诺现象迫使温跃层加深，将导致内部潮汐孔减少幼虫的运输，这一机制需要使温跃层变浅。其次，与厄尔尼诺中性条件下相比，在厄尔尼诺期间，滨海藤壶幼虫的分布将更深、更离岸，并较少受到近岸生境的限制，导致近岸幼虫丰度和定居减少。将通过a)部署一系列仪器来测量厄尔尼诺现象对南加州伯德岩近岸环流、水文、幼虫迁移和定居的影响；b)测量每日藤壶幼虫的沉降量；以及c)评估无脊椎动物幼虫的跨岸和深度分布。这些观测将与2014年(厄尔尼诺中性条件)和2015年(厄尔尼诺期间)在鸟岩进行的两年可比观测形成对比。此外，调查人员将测量Bird Rock和以北7公里处的Dike Rock的每周沉降量，在那里，1997/1998年厄尔尼诺现象结束时的先前观测表明，藤壶的沉降量非常高。这将使人们能够在厄尔尼诺现象减弱时评估定居点反应的一般性，并审查沿海岸线的定居点变化情况。

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.