Testing the sponge-loop hypothesis for Caribbean coral reefs

测试加勒比珊瑚礁的海绵环假说

• 批准号: 1558580
• 负责人: Christopher Finelli
• 金额: $ 81.8万
• 依托单位: University of North Carolina at Wilmington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-02-15 至 2021-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558580&HistoricalAwards=false
• 关键词: Testing; sponge; loop; hypothesis; Caribbean

Sponges are bottom-dwelling animals that dominate Caribbean reefs now that reef-building corals have been declining for decades. Sponges feed by filtering huge volumes of seawater, providing a mechanism for recycling organic material back to the reef. A new theory has been proposed called the "sponge-loop hypothesis" that is potentially the most important new concept in marine ecology in many years, because it seeks to explain Darwin's Paradox: how do highly productive and diverse coral reefs grow in desert-like tropical seas? The sponge loop hypothesis proposes that sponges on coral reefs absorb the large quantities of dissolved organic carbon (molecules such as carbohydrates) that are released by seaweeds and corals and return it to the reef as particles in the form of living and dead cells, or other cellular debris. This project will use a rigorous set of techniques to test the sponge-loop hypothesis in the field on ten of the largest and most common sponges on Caribbean reefs. For each species, the contributions of particles and dissolved organic carbon to sponge nutrition will be measured, as well as the production of cellular particles in the seawater flowing out of the sponge. For selected sponge species, the concentration of dissolved organic carbon entering the sponge will be experimentally enhanced to determine the capacity of the sponge to absorb this potential food source, and to gauge its effect on the production of cellular particles. This project will provide STEM education and training for postdoctoral, graduate and undergraduate students and public outreach in the form of easily accessible educational videos. Further, this project is important for understanding the carbon cycle on coral reefs where the effects of climate change and ocean acidification may be tipping the competitive balance toward non-reef-building organisms, such as sponges. The cycling of carbon from the water-column to the benthos is central to marine ecosystem function; for coral reefs, this process begins with photosynthesis by seaweeds and coral symbionts, which then exude a substantial portion of fixed carbon as dissolved organic carbon (DOC) that may be lost to currents and tides. But if sponges, with their enormous water filtering capacity, can return DOC from the water column to the reef, it would represent a major unrecognized source of carbon cycling. The "sponge-loop hypothesis" has the potential to transform our understanding of carbon cycling on coral reefs. Building on preliminary data from studies of the giant barrel sponge, this project will investigate each of the three components of the sponge-loop hypothesis for ten common barrel, vase and tube-forming species that span a range of associations with microbial symbionts, from high microbial abundance (HMA) to low microbial abundance (LMA) in the sponge tissue. Specifically, the experimental approach will include InEx techniques (comparative sampling of seawater immediately before and after passage through the sponge), velocimetry, and flow cytometry to determine whether each species consumes DOC and produces particulate organic carbon (POC) in the form of cellular detritus. Then, for species that consume DOC, the same techniques will be used in manipulative experiments that augment the amount of DOC from three categories (labile, semi-labile and refractory) to determine the types of DOC consumed by sponges. In addition to testing the sponge-loop hypothesis, this project will use molecular techniques to investigate the differences among HMA and LMA sponge species, targeting the microbial symbionts that may be responsible for DOC uptake.

海绵是生活在海底的动物，在加勒比海珊瑚礁中占主导地位，因为造礁珊瑚已经减少了几十年。海绵通过过滤大量海水为生，提供了一种将有机物质循环回珊瑚礁的机制。一种被称为“海绵环假说”的新理论被提出，这可能是多年来海洋生态学中最重要的新概念，因为它试图解释达尔文悖论：高产多样的珊瑚礁是如何在沙漠般的热带海洋中生长的？海绵环假说提出，珊瑚礁上的海绵吸收海藻和珊瑚释放的大量溶解的有机碳（碳水化合物等分子），并以活细胞和死细胞或其他细胞碎片的形式将其以颗粒的形式返回珊瑚礁。该项目将使用一套严格的技术，在加勒比海珊瑚礁上10种最大和最常见的海绵上实地测试海绵环假说。对于每个物种，将测量颗粒和溶解有机碳对海绵营养的贡献，以及从海绵流出的海水中细胞颗粒的产生。对于选定的海绵物种，将通过实验提高进入海绵的溶解有机碳浓度，以确定海绵吸收这种潜在食物来源的能力，并衡量其对细胞颗粒生产的影响。该项目将为博士后、研究生和本科生提供STEM教育和培训，并以易于获取的教育视频的形式向公众宣传。此外，这个项目对于了解珊瑚礁上的碳循环很重要，因为气候变化和海洋酸化的影响可能会使竞争平衡向非造礁生物倾斜，比如海绵。碳从水柱到底栖生物的循环是海洋生态系统功能的核心；对珊瑚礁来说，这个过程始于海藻和珊瑚共生体的光合作用，然后它们以溶解有机碳（DOC）的形式释放出相当一部分固定碳，这些固定碳可能会被水流和潮汐流失。但是，如果海绵具有巨大的水过滤能力，可以将DOC从水柱返回到珊瑚礁，它将代表一个未被认识的碳循环的主要来源。“海绵环假说”有可能改变我们对珊瑚礁碳循环的理解。基于对巨型桶状海绵研究的初步数据，本项目将研究海绵环假说的三个组成部分，包括10种常见的桶状、花瓶状和管状物种，这些物种与海绵组织中的微生物共生体有一系列关联，从高微生物丰度（HMA）到低微生物丰度（LMA）。具体来说，实验方法将包括InEx技术（在通过海绵之前和之后立即对海水进行比较采样）、测速法和流式细胞术，以确定每个物种是否消耗DOC并以细胞碎屑的形式产生颗粒有机碳（POC）。然后，对于消耗DOC的物种，将使用相同的技术进行操纵实验，从三个类别（不稳定，半不稳定和难降解）增加DOC的数量，以确定海绵消耗DOC的类型。除了测试海绵环假说外，该项目还将利用分子技术研究HMA和LMA海绵物种之间的差异，以可能负责DOC吸收的微生物共生体为目标。