Collaborative Research: Sponge Growth is Nitrogen Limited over the Shallow to Mesophotic Depth Gradient

珊瑚礁是众所周知的生物多样性热点，引起了公众和科学界的极大兴趣。世界各地的珊瑚礁目前正受到多种因素的威胁，如污染、沿海开发、过度捕捞和气候变化，热带水域的变暖和酸化导致珊瑚礁及其为我们提供的许多服务（如保护我们免受飓风破坏）的丧失。许多研究都集中在珊瑚上，珊瑚是许多珊瑚礁上明显占主导地位的生物群体，但其他生物也很重要。其中一组，海绵，对健康的珊瑚礁功能至关重要，因为它们为许多其他珊瑚礁生物提供食物和家园，它们显著地影响珊瑚礁的营养循环，它们合成生物医学界感兴趣的重要化合物。珊瑚礁科学的一个新兴领域是研究深度超过30米的深礁。这些珊瑚礁系统被称为中囊珊瑚礁生态系统，在技术潜水方法转移到科学界之前，它们在很大程度上是无法进入的。在这个项目中，研究人员将研究从3米到100米以上的海绵种群，以检查它们利用溶解和颗粒食物来源的能力，这可能有助于解释随着深度的增加，海绵生物多样性和生长速度的增加。该项目将为本科生和研究生以及退伍军人和博士后研究人员提供培训机会，特别是来自代表性不足的群体。此外，调查人员将为公众教育制定独特的外展计划。海绵是加勒比珊瑚礁群落中无处不在的成员，在那里它们扮演着多种角色。越来越多的证据表明，由于人为和自然因素导致珊瑚覆盖率下降，海绵种群数量正在增加。营养相互作用在控制物种分布和群落结构中起重要作用；然而，自上而下（捕食）和自下而上（营养资源）控制种群的相对重要性仍然是一个备受争议的话题。最近，有人提出海绵消耗大量的溶解有机碳（DOC）并释放大量的胆鞘细胞，这些胆鞘细胞为“海绵环”碎屑通路提供燃料，对更高的营养水平具有重要意义。要使“海绵环”假说得到广泛推广，一个很大程度上被忽视但却被明确指出的要求是，海绵必须表现出很少或没有净生长，这是平衡以海绵细胞（=碎屑）形式损失的碳的唯一途径，同时摄入颗粒有机碳（POC）和DOC；然而，海绵确实会生长。此外，在浅层和中厚层珊瑚礁（MCEs: 3-150m深度）上，海绵为食的浮游细菌资源存在很强的垂直梯度，海绵的存在促进了浮游细菌的生长，这表明颗粒有机碳（POC）的重要性。到目前为止，在这个讨论中遗漏了溶解和颗粒有机氮（DON/PON）的重要作用，这对珊瑚礁上的海绵生长至关重要。该提案有两个目标：1)量化以前从未做过的浅层到中深水深度梯度上可用的DOC/POC和DON/PON资源；2)通过广泛的海绵分类表示（包括浅层到中深水的多种生活史策略）量化对这些资源的深度依赖。为了完成第二项任务，研究人员将对海绵从浅层到中水深的生长进行研究，以梳理DOC/POC和DON/PON在海绵生长中的独立和交互作用。他们还将为利用这些资源的海绵构建碳、氮和能量预算。该项目将首次提供若干珊瑚礁的DOC/POC和DON/PON的全面清单。这将通过对浅层到中水深梯度的取食和生长的研究加以补充。随着浅层和中叶珊瑚礁群落结构的持续变化，了解我们是否可以使用生态系统功能模型预测哪些珊瑚礁将经历向海绵主导群落的转变，以及促成这些转变的因素，将对当地海洋资源管理者有用。这些数据还将为更广泛的海洋生态学领域提供信息，并为介孔珊瑚礁的结构和功能提供新的见解。最后，从中孔珊瑚礁收集的海绵样本通常代表新物种，并将根据科学家的要求提供给他们。

Coral reefs are well known biodiversity hotspots of considerable interest to the public and scientific community. Reefs around the world are currently under threat from multiple factors such as pollution, coastal development, overfishing and climate change, where both the warming and acidification of tropical waters contributes to the loss of coral reefs and the many services they provide for us, such as protection from hurricane damage. Many studies are focused on corals, the conspicuously dominant group of organisms on many coral reefs, but other organisms are also important. One group, sponges, are essential for healthy reef function as they provide food and homes for many other reef organisms, they dramatically effect the nutrient cycles on reefs, and they synthesize important compounds of interest to the biomedical community. An emerging area of coral reef science is the study of deep reefs at depths greater than 30 meters. These coral reef systems, known as mesophotic coral reef ecosystems, were largely inaccessible until the transfer of technical diving approaches to the scientific community. In this project the investigators will study sponge populations from 3 meters to over 100 meters to examine their ability to utilize both dissolved and particulate food sources that may help explain increasing sponge biodiversity and growth rates with increasing depth. This project will provide training opportunities for undergraduate and graduate students as well as veterans and post-doctoral researchers, especially from underrepresented groups. Additionally, the investigators will develop unique outreach programs for public education.Sponges are ubiquitous members of Caribbean coral reef communities, where they have multiple roles. There is evidence accumulating that sponge populations are increasing as coral cover declines due to anthropogenic and natural factors. Trophic interactions play crucial roles in controlling the distributions of species and community structure; however, the relative importance of top-down (predation) and bottom-up (nutrient resources) control of populations remains a hotly debated topic. Recently, it has been proposed that sponges consume large amounts of dissolved organic carbon (DOC) and release large numbers of choanocytes that fuel a "sponge loop" detrital pathway of significance to higher trophic levels. A largely overlooked, but clearly stated, requirement for the "sponge-loop" hypothesis to be broadly generalizable is that sponges must exhibit little, or no, net growth as the only way to balance the loss of carbon in the form of choanocytes (=detritus), with the intake of both particulate organic carbon (POC) and DOC; however, sponges do grow. Additionally, on both shallow and mesophotic coral reefs (MCEs: 3-150m depth), there is a strong vertical gradient in bacterioplankton resources on which sponges feed, and enhanced growth in the presence of spongivory argues for the importance of particulate organic carbon (POC). Missing so far in this discussion is the important role of dissolved and particulate organic nitrogen (DON/PON) that would be essential for sponge growth on coral reefs. This proposal has two goals: 1) quantify the DOC/POC and DON/PON resources available across the shallow to mesophotic depth gradient that has never been done before, and 2) quantify the depth dependence on these resources by a broad taxonomic representation of sponges that also includes multiple life-history strategies across shallow to mesophotic depths. To accomplish this second task the investigators will conduct studies on the growth of sponges from shallow to mesophotic depths to tease apart the independent and interactive roles of DOC/POC and DON/PON in sponge growth. They will also construct carbon, nitrogen and energetic budgets for sponges utilizing these resources. The project will provide the first comprehensive inventory of DOC/POC and DON/PON on several coral reefs. This will be complemented by studies of feeding and growth across the shallow to mesophotic depth gradient. With continuing changes in the community structure of both shallow and mesophotic reefs, understanding whether we can predict, using models of ecosystem function, which reefs will undergo transitions to sponge dominated communities and what factors contribute to these transitions, will be of use to local marine resource managers. These data will also inform the broader field of marine ecology, as well as provide new insights into mesophotic reef structure and function. Finally, sponge samples collected from mesophotic coral reefs often represent new species and they will be made available to scientists upon request.