Collaborative Research: The Influence of Sponge Holobiont Metabolism on Coral Reef Dissolved Organic Matter and Reef Microorganisms

珊瑚礁周围的海水通常营养成分较低，但珊瑚礁却充满了生命，经常被比作沙漠中的绿洲。生命之所以存在于这些“海洋沙漠”中，很大程度上是由于单细胞微生物与珊瑚和海绵等无脊椎动物之间的共生关系。溶解有机物（DOM）的浓度和类型也会影响珊瑚礁的健康。DOM是一种复杂的有机营养物，如氨基酸、维生素和其他多种化合物。珊瑚礁上DOM的组成与海水中自由生活的微生物的组成以及滤食性生物（如珊瑚和海绵）的营养有关。然而，影响珊瑚礁上DOM组成的因素及其变化的后果尚不清楚。最近的研究表明，海绵可能对珊瑚礁溶解有机营养物质的组成产生重大影响，这取决于海绵物种的过滤能力及其共生微生物群落的差异。该项目描述了不同的海绵物种如何在珊瑚礁上处理DOM，并确定了这种处理对自由生活的微生物群落的影响。在库拉索岛相对原始的地区，从珊瑚礁上的海绵（海绵过滤前和海绵过滤后）中收集海水，并进行孵化实验，测量海绵过滤对自由生活微生物群落生长的影响。采用尖端技术分析海水样品的有机营养成分，以区分海绵处理的营养成分类型。利用从珊瑚礁收集的自由生活微生物进行的孵化实验，量化了海绵过滤对该群落生长和组成的影响。这个项目提供了对海绵如何为珊瑚礁食物网的基础做出贡献的基本理解。随着人类驱动的影响不断改变珊瑚礁上生物的组成，这种理解对于预测珊瑚礁微生物食物网的变化是必要的，因此对科学家、珊瑚礁管理者和政策制定者来说是必不可少的。该项目培养本科生和一名博士后学者，并通过开发以海绵为中心的课程，重点关注美国东海岸当地的水生环境和珊瑚礁生态系统，为本科和K-12教育做出贡献。海绵过滤海水的能力和与之相关的微生物群落各不相同，导致不同的代谢策略经常在一个栖息地共存。虽然海绵在处理溶解有机物（DOM）方面很重要，这是还原碳化合物的重要储存库，并将这种能量转移到底栖食物网，但了解海绵处理对珊瑚礁DOM组成和远洋食物网的影响的工作有限。具体来说，虽然研究表明珊瑚和藻类的分泌物会选择特定的浮游生物（分别为自养和异养），但要了解影响DOM组成和珊瑚礁上浮游生物群落组成的多种因素，还需要海绵的类似数据。因此，本项目旨在解决海绵衍生DOM（海绵外代谢组）在珊瑚礁生物地球化学中作用的主要知识差距。针对著名的加勒比海绵和微微浮游生物孵化实验的原位采样设计相结合，以解决海绵外代谢组的组成和描绘由海绵外代谢组衍生的微微浮游生物群落的变化。通过两种DOM分析技术，即常用的荧光测定技术（fDOM分析）和高分辨率质谱法（LC-MS/MS），评估了海绵处理对海水DOM的分子水平变化以及这些变化对整个珊瑚礁DOM剖面的影响。此外，微生物组和功能基因谱、生长指标和营养分析被用于评估微浮游生物群落对海绵外代谢组的响应变化。然后，先进的数据分析技术将每种方法生成的数据综合起来，为珊瑚礁上尚未表征的生物地球化学途径提供新的见解。这里概述的工作代表了海绵代谢对DOM组成影响的全新信息，揭示了参与底-上层耦合的生物学重要分子，重要的是，使用标准化方法生成数据，从而便于与以前和未来的DOM数据集进行比较。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The seawater around coral reefs is typically low in nutrients, yet coral reefs are teeming with life and are often compared to oases in a desert. Life exists in these 'marine deserts' in large part, due to symbiotic associations between single-celled microbes and invertebrates such as corals and sponges. The concentration and type of dissolved organic matter (DOM), a complex pool of organic nutrients such as amino acids, vitamins, and other diverse compounds, also affects the health of coral reefs. The composition of DOM on coral reefs is linked to both the composition of free-living microbes in the seawater and to the nutrition of filter-feeding organisms, such as corals and sponges. However, the factors that influence the composition of DOM on coral reefs and the consequences of how it changes are not well understood. Recent work suggests that sponges could have a significant impact on the composition of reef dissolved organic nutrients, depending on sponge species due to differences in filtration capacity and in their symbiotic microbial communities. This project characterizes how diverse sponge species process DOM on coral reefs and determines the impacts of this processing on the free-living microbial community. Seawater is collected from sponges (pre- and post- sponge filtration) on coral reefs in the relatively pristine region of Curacao, and incubation experiments measure the impact of sponge filtration on the growth of the free-living microbial community. The organic nutrients of seawater samples are analyzed using cutting-edge techniques to distinguish the types of nutrients that are processed by sponges. The incubation experiments, using free-living microbes collected from the coral reef, quantify the impact of sponge filtration on the growth and composition of this community. This project provides fundamental understanding of how sponges contribute to the base of the coral reef food web. As the human-driven impacts continue to alter the composition of organisms on reefs, this understanding is necessary to predict changes to reef microbial food webs and is thus essential for scientists, reef managers, and policy decision makers. This project trains undergraduate students and a postdoctoral scholar and contributes to undergraduate and K-12 education through development of sponge-centric lessons that focus on local U.S. east coast aquatic environments as well as coral reef ecosystems. Sponges vary in their capacity to filter seawater and in their associated microbial communities, leading to diverse metabolic strategies that often coexist in one habitat. While it is well-established that sponges are important in processing dissolved organic matter (DOM), an important reservoir of reduced carbon compounds, and transferring this energy to benthic food webs, there has been limited work to understand the consequences of sponge processing on the composition of coral reef DOM and on pelagic food webs. Specifically, while studies have shown that exudates of corals and algae select for specific groups of picoplankton (autotrophic and heterotrophic, respectively), similar data for sponges are required to understand the multiple factors that shape the composition of DOM and of the picoplankton community on coral reefs. Thus, this project is aimed at addressing a major knowledge gap of the role of sponge-derived DOM (sponge exometabolome) in coral reef biogeochemistry. An in situ sampling design targeting prominent Caribbean sponges and picoplankton incubation experiments is coupled to address both the composition of sponge exometabolomes and delineate shifts in the picoplankton community derived from sponge exometabolomes. Molecular-level changes to seawater DOM by sponge processing and the impact of these changes on the overall coral reef DOM profile is assessed with two DOM analysis techniques: a commonly used fluorometry technique (fDOM analysis) and with high-resolution mass spectrometry (LC-MS/MS). Additionally, microbiome and functional gene profiling, growth metrics, and nutrient analyses are employed to assess changes in the picoplankton community in response to sponge exometabolomes. Advanced data analysis techniques then synthesize data generated by each approach to provide novel insight on a poorly uncharacterized biogeochemical pathway on coral reefs. The work outlined here represents entirely novel information on the impact of sponge metabolism on the composition of DOM, sheds light on biologically important molecules involved in benthic-pelagic coupling, and importantly, generates data using standardized methods, thus facilitating comparison to previous and future DOM datasets.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.