Chemical ecology of sponges on Caribbean coral reefs

海绵现在是大多数加勒比海珊瑚礁上主要的栖息地形成动物。与珊瑚和一些大型藻类不同，海绵有未钙化的骨骼，不容易受到海洋酸化的影响。最近发表的一项关于佛罗里达群岛珊瑚礁上巨型桶状海绵的人口统计研究表明，2000年至2006年间，这种海绵的数量增加了约40%。这个更新项目将调查加勒比海珊瑚礁海绵的化学生态学，这一群体的分类和次生代谢产物已经得到了很好的描述。一些珊瑚礁海绵产生化学防御，而另一些则受到鱼类捕食者的放牧。集体群落分布在一个大的生物地理区域，在那里，各种人为影响允许测试关于生态系统功能、间接影响和资源分配的基本假设。知识价值：以前nsf资助的研究已经改变了对加勒比海珊瑚礁生态系统的理解。对70多种加勒比海绵的化学、结构和营养抗掠食性防御进行了调查，然后利用珊瑚礁鱼类的自然种群进行了实地试验，结果从15多种海绵中分离和鉴定出了威慑化合物。一系列的操纵实验清楚地表明，吃海绵的鱼类限制了海绵的分布，而鹦嘴鱼是主要的海绵体动物，从而推翻了关于吃海绵的鱼类对珊瑚礁群落影响的传统观念。新的凝胶分析揭示了海绵代谢物对其他海绵和珊瑚物种的不同化感作用。因此，加勒比珊瑚礁的生态系统模型涉及营养和竞争相互作用，预测了其他生态系统已知的级联和间接影响。测试生态系统模型的三个主要目标是：(1)扩展对海绵群落自上而下控制的研究。在世界资源研究所“濒危珊瑚礁”数据库的指导下，将对加勒比次区域过度捕捞与保护良好的珊瑚礁上的海绵及其捕食者的群落结构进行预测和比较。在不同受影响的珊瑚礁上进行食物选择实验时，鹦嘴鱼捕食海绵的过程将被录像。海绵和珊瑚之间的化感竞争相互作用（珊瑚光合作用和漂白的海绵代谢物）的研究将继续使用改进的凝胶基现场试验和潜水- pam荧光法；(2)改进对另一种假设的检验，即自下而上的过程——微浮游生物作为食物的可用性——控制着珊瑚礁群落。捕食者排除实验将在微浮游生物丰富和贫乏、深礁和浅礁地点分离捕食对海绵生长的影响；(3)拓展海绵生命史在化学防御、生长和繁殖之间资源分配权衡的研究。人工礁表面已知年龄的海绵群落在招募和演替方面的差异将被研究。这部分内容建立在最近在佛罗里达州基拉戈附近的Spiegel Grove沉船甲板上发现的海绵群落演代上，这强烈表明了化学防御与繁殖或生长之间的资源权衡。更广泛的影响:该研究项目的更新将提供(1)在教学密集型，主要是硕士水平的大学为本科生和研究生提供支持和培训（68%的直接成本用于学生支持），(2)科学家与来自美国和国外的学生合作进行三次为期两周的研究巡航，(3)基于网络的外展，包括人口统计，漂白，和加勒比海绵的化学防御，并进一步改进加勒比海绵易于使用的摄影钥匙。该项目的结果将有助于判断从陆地生态系统研究中得出的化学防御理论的普遍适用性，同时促进对珊瑚礁环境中底栖无脊椎动物、它们的捕食者和它们的竞争对手之间复杂关系的理解，在珊瑚礁环境中，全球气候变化和海洋酸化的影响可能会使竞争平衡向非钙化生物倾斜，如海绵。

Sponges are now the dominant habitat-forming animals on most Caribbean coral reefs. Unlike corals and some macroalgae, sponges have uncalcified skeletons, and are less prone to effects of ocean acidification. A recently published demographic study of the giant barrel sponge on the Florida Keys reefs showed population increases by ~40% between 2000 and 2006. This renewal project would investigate the chemical ecology of Caribbean reef sponges, a group whose taxonomy and secondary metabolites are well described. Some reef sponges produce chemical defenses, while others are subject to grazing by fish predators. The collective community is found over a large biogeographic area where variable anthropogenic impacts permit the testing of fundamental hypotheses about ecosystem function, indirect effects, and resource allocation. Intellectual merits: Previous NSF-funded research has transformed understanding of Caribbean coral reef ecosystems. A survey of chemical, structural and nutritional anti-predatory defenses of over 70 species of Caribbean sponges, followed by field experiments using natural populations of reef fishes, resulted in the isolation and identification of deterrent compounds from over 15 species. A series of manipulative experiments clearly demonstrated that sponge-eating fishes limit sponge distributions, and that parrotfishes are major spongivores, thereby overturning conventional ideas about effects of sponge-eating fishes on reef communities. Novel gel-based assays revealed differential allelopathic effects of sponge metabolites against other sponge and coral species. The ecosystem model for Caribbean reefs thus involves trophic and competitive interactions, predicting cascades and indirect effects known for other ecosystems. Three primary objectives for testing the ecosystem model are to: (1) extend studies of top-down control of the sponge community. Guided by the World Resources Institute "Reefs at Risk" database, predictions and comparisons will be made of the community structure of sponges and their predators on overfished vs. well-protected reefs across sub-regions of the Caribbean. Parrotfish predation on sponges will be video recorded during food choice experiments on differently impacted reefs. Studies of allelopathic competitive interactions between sponges and corals (sponge metabolites on coral photosynthesis and bleaching) will continue using a modified gel-based field assay and diving-PAM fluorometry; (2) improve testing of the alternative hypothesis that bottom-up processes -- availability of picoplankton as food -- control reef communities. Predator-exclusion experiments will decouple effects of predation from sponge growth at picoplankton-rich and -poor, deep- and shallow-reef sites; (3) expand studies of sponge life history trade-offs in resource allocation between chemical defense, growth and reproduction. Differences in recruitment and succession will be examined among sponge communities of known age on artificial reef surfaces. This component builds on the recent discovery of sponge community succession on the deck of the Spiegel Grove shipwreck off Key Largo, FL, which strongly suggests a resource trade-off between chemical defenses and reproduction or growth. Broader impacts: Renewal of this research program will provide (1) support and training for undergraduate and graduate students at a teaching-intensive, predominantly MS-level university (68% of direct costs for student support), (2) collaboration between scientists and students from the US and abroad on three 2-week research cruises, (3) web-based outreach, including updated links on the demographics, bleaching, and chemical defenses of Caribbean sponges and further refinement of an easy-to-use photographic key to sponges of the Caribbean. Results of this project will be useful in judging the general applicability of chemical defense theories derived from studies of terrestrial ecosystems, while advancing understanding of the complex relationships between benthic invertebrates, their predators and their competitors in coral reef environments where the effects of global climate change and ocean acidification may be tipping the competitive balance toward non-calcifying organisms, such as sponges.