RAPID: Testing the ability of the 2015-2017 El Nino Southern Oscillation (ENSO) to drive a community-level regime shift in the Galapagos marine ecosystem

各类生境的生态结构、生物多样性和生态系统功能都发生了变化。有时变化是如此之大和突然，生态系统切换到一个交替的状态或制度，持续很长一段时间（即几十年到几千年），如撒哈拉沙漠植被和沙漠生态系统之间的转换。 由于制度变化可能会极大地改变生态系统为人类提供的货物和服务，因此在实践和理论上都需要了解导致不同制度之间临界点的条件和驱动因素。到目前为止，很少有人知道的前提条件或驱动程序的政权变化，特别是在潮下带生境，在政权变化之前，相互作用的物种群落的生态状态的长期数据是很难获得的。关于海洋栖息地热带状态变化的大部分知识都集中在珊瑚和大型藻类之间的变化上，尽管这些生物只代表物种丰富的生态系统的一部分，该生态系统具有许多可能的状态变化轨迹和结果。因此，拟议调查的首要目标是测试本文开发的概念模型，预测2016年异常强烈的厄尔尼诺南方涛动（厄尔尼诺南方涛动）的厄尔尼诺和拉尼娜阶段如何在整个社区层面推动加拉帕戈斯岩石潮下带的政权转变。由于目标群落除藤壶、甲壳珊瑚藻、珊瑚、海胆、海星和掠食性鱼类外，还将海绵作为一个关键组成部分，该模型检验了海绵礁假说的预测，这是一个新出现的范例，预测随着珊瑚因未来气候变化而减少（代表珊瑚到海绵的状况变化），海绵可能会越来越多地主宰空间。 初步数据表明，相反的SRH，海绵下降期间异常温暖的温度在本厄尔尼诺/南方涛动开始在加拉帕戈斯潮下带社区。然而，海胆捕食海绵和CCA似乎在同一时间加速，因此建议进行操纵性现场实验，严格测试和区分ENSO温度升高对海绵死亡率的影响，增强海胆捕食海绵的影响。这些实验结果将在整个厄尔尼诺/南方涛动期间，通过对加拉帕戈斯中部12个地点的底栖生物群落重新进行定量取样，在整个群落的实际长期（13-16年）变化的范围内进行评价。 对这一基线进行重新抽样也将有助于分析导致假设政权更迭的指标。该项目将在从高中生到研究生和公众的各个层面产生更广泛的教育影响，虽然在许多生态系统中，状态变化被描述为响应自然或人为驱动因素而突然转变为交替的持久状态，但对热带海洋底栖群落状态变化的研究主要集中在从珊瑚主导的状态转变为大型藻类主导的状态。这种狭隘的关注忽视了固着无脊椎动物的多样组合的潜在影响，例如海绵，它们与珊瑚共享珊瑚礁坚硬基底上的空间，如果珊瑚减少，它们可能会作为一个新的政权扩散。SRH是一种新兴的社区生态范式，它假定海绵可能会越来越多地主导空间，因为珊瑚会因未来的气候变化和海洋酸化而减少，但它尚未经过严格的测试。在加拉帕戈斯群岛发生的异常强烈的厄尔尼诺现象提供了一个独特的机会，可以评估气候波动在社区一级造成状况变化的潜力，并测试SRH，因为自1999年以来，在加拉帕戈斯群岛中部的多个地点，至少每年都对潮下底栖生物群落结构进行量化。最近的2015年调查表明，与目前的厄尔尼诺变暖相一致，多个地点的海绵死亡率显着，与SRH相反。然而，海胆捕食海绵和甲壳珊瑚藻（CCA）似乎在同一时间加速，所以操纵现场实验，建议严格测试和区分ENSO升高的温度对海绵死亡率的影响增强海胆捕食海绵的影响。更具体地说，八个主要的假设沿着与四个备用假设的开发和提出了一个新的概念模型预测直接和间接途径的制度变化的社区CCA，海绵，藤壶，珊瑚，海胆，海星和掠食性鱼类。这项研究将在2016-2017年厄尔尼诺和拉尼娜阶段的四次旅行中，在加拉帕戈斯群岛中部12个社区基线地点的岩石潮下带进行。拟议的实验和观测（即基线重新取样）相结合的方法将能够严格评估气候引起的热带海底生态系统状况变化的直接和间接途径。

Changes in the ecological structure, biodiversity and functioning of ecosystems have occurred in all types of habitats. Sometimes the change is so large and abrupt that the ecosystem switches to an alternate state, or regime, that persists for long periods of time (i.e. decades to millennia) such as the switch between a vegetated and desert ecosystem in the Sahara. Since regime changes may drastically alter the ecosystem goods and services provided to humankind, there is a practical as well as theoretical need to understand the conditions and drivers leading to tipping points between alternate regimes. To date, little is known about either the pre-conditions or drivers of regime change, particularly in subtidal habitats where long-term data on the ecological state of communities of interacting species prior to regime change is difficult to obtain. Most of the knowledge about tropical regime shifts in marine habitats has focused on shifts between corals and macroalgae even though these organisms represent only part of a species-rich ecosystem with many possible trajectories and outcomes of regime change. Consequently, the overarching goal of the proposed investigation is to test a conceptual model developed herein predicting how both El Niño and La Niña phases of the unusually strong 2016 ENSO (El Niño Southern Oscillation) may drive a regime shift in the Galapagos rocky subtidal at the whole community level. As the target community involves sponges as a key component, in addition to barnacles, Crustose Coralline Algae (CCA), corals, sea urchins, sea stars and predatory fish, the model tests predictions from the Sponge Reef Hypothesis (SRH), an emerging paradigm predicting that sponges may increasingly dominate space as corals decline from future climate change (representing a coral to sponge regime change). Preliminary data indicate that counter to the SRH, sponges declined during the unusually warm temperatures at the outset of the present ENSO in Galapagos subtidal communities. However, sea urchin predation on sponges and CCA appears to have accelerated at the same time, so manipulative field experiments are proposed to rigorously test and differentiate the effects of ENSO elevated temperature on sponge mortality from the effects of enhanced sea urchin predation on sponges. These experimental results will be evaluated in the context of actual, long-term (13-16 year) changes in the whole community obtained by quantitative re-sampling of the benthic community at 12 sites in the central Galapagos throughout the present ENSO. Re-sampling this baseline will also enable the analysis of indicators leading up to the hypothesized regime change. Broader educational impacts of the project will transpire at all levels from high school students to graduate students and the public.Although regime changes have been described as abrupt shifts to alternate, persistent states in many ecosystems in response to natural or anthropogenic drivers, research on regime change in bottom-dwelling communities of tropical oceans has largely focused on a switch from coral-dominated to macroalgal- dominated regimes. This narrow focus overlooks potential influences of the diverse assemblages of sessile invertebrates such as sponges that share space on the hard substrate of reefs with corals and could proliferate as a new regime if corals are diminished. The SRH is an emerging community ecological paradigm that posits that sponges may increasingly dominate space as corals decline from future climate change and ocean acidification, yet it has not been rigorously tested. The exceptionally strong El Niño occurring in the Galapagos Islands presents a unique opportunity evaluate the potential for climate oscillations to create regime shifts at the community level and to test the SRH because subtidal benthic community structure has been quantified at least annually since 1999 at multiple sites in the central Galapagos Islands. Recent 2015 surveys indicated significant mortality of sponges at multiple sites coincident with the present El Niño warming, counter to the SRH. However, sea urchin predation on sponges and Crustose Coralline Algae (CCA) appears to have accelerated at the same time, so manipulative field experiments are proposed to rigorously test and differentiate the effects of ENSO elevated temperature on sponge mortality from the effects of enhanced sea urchin predation on sponges. More specifically, eight main hypotheses along with four alternate hypotheses are developed and proposed from a new conceptual model predicting direct and indirect pathways of regime change in a community of CCA, sponges, barnacles, corals, sea urchins, sea stars and predatory fish. The research will be performed in the rocky subtidal at the 12 community baseline sites in the central Galapagos archipelago during four trips in 2016-2017 bracketing the El Niño and La Niña phases. The proposed combination of experimental and observational (i.e. baseline re-sampling) methods will enable a rigorous evaluation of climate-induced direct and indirect pathways of regime change in tropical benthic ecosystems.