Ocean Acidification, Temperature and Light Effects on Carbon-use Mechanisms, Calcification, and Growth of Tropical Macroalgae: Drivers of Winners and Losers

海洋对大气中二氧化碳的封存提高了海水中二氧化碳的有效性，降低了海洋的pH值，通常被称为“海洋酸化”。海洋大型藻类可能会对海洋化学的这两个变化(二氧化碳升高和酸化)作出反应，其方式可能会降低珊瑚礁和其他沿海生态系统的可持续性，带来潜在的经济后果。珊瑚礁上有两种主要的海洋大型藻类：一种是肉质藻类，其特征是生长潜力很快，使它们成为令人讨厌的物种，并在竞争中胜过珊瑚；另一种是钙化物种，生长较慢，但有助于巩固珊瑚礁，促进珊瑚幼体的定居。目前，关于肉质大型藻类光合作用和生长对海洋二氧化碳增加的反应的信息很少。此外，对海洋酸化对大型藻类钙化的影响了解不足。这项拟议的研究将考察模拟未来海洋酸化的一系列pH和CO2水平上无机碳吸收光合作用的基本途径(2100)。还将研究海洋酸化下光合作用、生长和钙化是如何受光和温度调节的。这些数据将被用来确定海洋酸化对具有重要生态意义的大型藻类的影响以及由此对珊瑚礁生态系统的影响。这项关于海洋大型藻类的研究增加了我们对海洋酸化对海洋钙化物的影响的理解，这是国家海洋委员会确定的研究重点。该研究机构位于Gumbo Limbo(GL)自然中心，每年接待10万名游客，并有教育项目支持每年15,000名K-12学生。这项研究与已建立的外展设施并列在一起，为向广大公众受众传播开放式获取科学及其社会影响提供了独特的机会。与浮游植物和微藻相比，大型藻类对海洋酸化的反应可能是不同的，因为它们的表面积与体积比低，外边界层对二氧化碳的抵抗力高，对辐射的要求也更高。了解热带大型藻类光合作用和钙化对升高的二氧化碳、温度和光照的具体机制响应，对于预测以大型藻类为主的热带群落，包括那些生长在其温度极限附近的群落，是至关重要的。本研究的目的是：(1)对光合作用和钙化的生物化学和生理学提供新的见解，以驱动热带大型藻类对光合作用和气候变暖的生长反应；(2)阐明热带物种光合作用的碳利用机制，以了解光合作用对HCO3利用的影响；(3)确定光合作用-钙化过程是否被光合作用-钙化过程解偶联；(4)阐明光合作用和钙化作用在光合作用和钙化反应中的作用；(5)研究光合作用、温度和光照对生活在接近其温度极限的物种光合作用和生长的热最适温度的协同效应。为了实现这些目标，将进行一系列短期生理实验，以确定10种主要肉质和钙质热带大型藻类的HCO3利用机制、Ci吸收动力学、利用碳聚集机制(CCM)的潜力以及光合作用C利用机制与钙化之间的物种特异性联系。这些生化和生理数据随后将用于解释在三个不同季节进行的水族研究中的较长期(20d)生长(有机和无机钙化和晶体形成)反应，以及光合作用响应面实验对pH、辐射和温度梯度的影响。

Ocean sequestration of atmospheric CO2 enhances the availability of CO2 in seawater and lowers ocean pH, commonly referred to as 'ocean acidification'. Marine macroalgae are likely to respond to these two changes in ocean chemistry (elevated CO2 and acidification) in ways that have the potential to reduce the sustainability of coral reefs and other coastal ecosystems with potential economic consequences. There are two major forms of marine macroalgae on reefs: fleshy species that are characterized by a rapid growth potential which allows them to become 'nuisance species' and out-compete corals, and calcified species that are slower growing, but help cement the reef and promote coral larval settlement. Currently, there is very little information on fleshy macroalgal photosynthesis and growth responses to increased ocean CO2. Further, there is an inadequate understanding of ocean acidification effects on macroalgal calcification. The proposed research will examine the fundamental pathways of inorganic carbon uptake for photosynthesis across a range of pH and CO2 levels simulating ocean acidification into the future (2100). How photosynthesis, growth and calcification are modulated by light and temperature under ocean acidification will also be examined. These data will be used to identify ocean acidification effects on ecologically important macroalgae and consequential impacts to coral reef ecosystems. This research on marine macroalgae increases our understanding of ocean acidification effects on marine calcifiers, a research priority identified by the National Ocean Council. The research facility is sited at The Gumbo Limbo (GL) Nature Center that receives 100,000 visitors/yr and has educational programs supporting 15,000/yr K-12 students. This juxtaposition of research with an established outreach facility provides a unique opportunity to communicate OA science and its societal implications to a large public audience. Macroalgae responses to ocean acidification (OA) are likely to be distinctive compared to phytoplankton and microalgae due to their low surface area to volume ratios, high external boundary layer resistance to CO2 and higher irradiance requirements. Understanding specific mechanistic responses of tropical macroalgal photosynthesis and calcification to elevated pCO2, temperature and irradiance is critical to develop predictions of OA effects on macroalgal dominated communities of the tropics, including those that grow near their thermal limits. The research objectives are to (1) provide new insights into the biochemistry and physiology of photosynthesis and calcification that drive growth responses to OA and warming in ecologically important tropical macroalgal species, (2) elucidate photosynthetic C-use mechanisms in tropical species to understand OA influences on HCO3- use, (3) determine if photosynthesis-calcification processes become uncoupled by OA, (4) clarify the role of irradiance in photosynthetic and calcification responses to OA, and (5) examine the synergistic effects of OA, temperature and light on the thermal optima of photosynthesis and growth in species living close to their thermal limits. To meet these objectives, a series of short-term physiological experiments will be conducted to ascertain HCO3-use mechanisms, Ci uptake kinetics, potential to employ carbon concentrating mechanisms (CCMs), and species-specific linkages between photosynthetic C-use mechanisms and calcification in ten dominant fleshy and calcareous tropical macroalgae species. These biochemical and physiological data will subsequently be used to interpret longer-term (20 d) growth (organic and inorganic calcification and crystal formation) responses in aquaria studies conducted over three different seasons, and photosynthesis response surface experiments to gradients of pH, irradiance and temperature.