Trophic ecology of small hydromedusae: a new perspective on their function in coastal ecosystems

研究的重点是小水母(钟形直径5 mm)的营养作用。水母是重要的、通常具有高度选择性的浮游捕食者，可以强烈影响后生浮游动物的现存量以及鱼卵和幼虫。导致大型、显眼水母成功的摄食率、猎物选择模式和潜在的摄食机制已经得到了很好的研究。然而，大多数水母都很小。这些小型水母种类丰富，分类多样，通常具有世界性的分布。然而，尽管它们是海洋中最大、最多样化的胶状浮游动物群体，但它们的觅食生态实际上是未知的。初步数据表明，许多小型水母与它们体型较大的近亲相比，食物不同，营养作用也不同。这些初步研究表明，一些小的水母类物种(1)以包括浮游植物在内的微型浮游生物为食，(2)数量足够多，摄食率足够高，足以清除季节性出现的沿海生态系统中相当大比例的浮游植物。该项目将解决这样一种假设，即高丰度和高摄食率的组合使小型水母能够在季节性生产高峰期作为重要的浮游植物捕食者。因此，认为水母主要是浮游后生动物的捕食者的当代范例可能需要进行重大修订，以涵盖小型水母的营养作用。这项研究的目的是通过研究小型水母在罗德岛纳拉甘西特湾的营养作用来检查它们的摄食过程和影响。我们将使用(1)量化小型水母对罗德岛纳拉甘西特湾浮游生物群落的营养影响和(2)量化它们摄食和猎物选择的功能基础的综合方法。拟议活动的智力价值：这项研究将导致对群落摄食率、猎物选择模式和潜在摄食机制的新理解，这些机制导致了水母类中最多样化的分类群体的成功和进化寿命。如果小型水母主要作为杂食性动物以微型浮游生物为食，并能够显著影响微型浮游生物的现存量，那么这项研究将证明后生动物和微生物食物网之间存在新的重要营养联系。这一新知识将使原生生物生态学家更好地了解控制微型浮游生物现存量和生产率的因素。这项研究还将使进化生态学家更好地了解影响小型水母身体形态和功能进化的生物力学因素，以及原生动物的行为和身体形态。从这个角度来看，这项研究直接涉及了解影响生物多样性的因素及其在海洋系统中的生态后果的问题，这是美国国家科学基金会生物海洋学部门强调的一个具体主题。拟议活动的更广泛影响：该项目将通过记录远洋食物网中一种新的、但想必是常见的营养联系，鼓励科学发现。来自两个主要是本科生机构和一个主要是研究生机构的科学家的参与增加了培训和指导的机会。每所院校都将让学生参与研究的各个方面(在提案的每一年，5名本科生，2名来自威斯康星大学，2名来自PC；1名来自URI海洋生物学项目的本科生将在每个项目年度的春季学期与Gifford一起学习一门独立的学习课程(15学分))。在收到资助后，吉福德将申请预算补充资金，以支持一名中学科学教师在暑期参与该项目。与过去一样，我们将利用我们与公众教育媒体(广播、电视纪录片、新闻文章和水族馆展品)的接触来交流我们对美杜山生态的新发现。我们与这些机构与公众的持续对话使我们有机会向广大公众传达我们的调查结果，并教育公众。

The focus of the research is the trophic role of small (bell diameter 5 mm) hydromedusae. Medusae are important, often highly selective, planktonic predators that can strongly affect standing stocks of metazoan zooplankton as well as fish eggs and larvae. The feeding rates, prey selection patterns and the underlying feeding mechanisms that have led to the success of large, conspicuous medusae have been well studied. However, most medusae are small. These small medusae are abundant, taxonomically diverse, and often have cosmopolitan distributions. Yet their feeding ecology is virtually unknown despite their status as the largest and most diverse group of gelatinous zooplankton in the sea. Preliminary data indicate that many small hydromedusae feed differently and have different trophic roles than their larger relatives. These preliminary studies have shown that some small medusan species (1) feed as omnivores on microplankton, including phytoplankton and (2) are sufficiently abundant and have sufficiently high feeding rates to remove a significant proportion of the phytoplankton standing stock in the coastal ecosystems where they occur seasonally. This project will address the hypothesis that this combination of high abundance and high feeding rates enables small hydromedusae to function as significant grazers of phytoplankton during periods of peak seasonal production. Consequently, the contemporary paradigm that medusae are primarily predators of planktonic metazoans may require significant revision in order to encompass the trophic role of small hydromedusae. The goal of the research is to examine the feeding processes and impact of small hydromedusae by examining their trophic role in Narragansett Bay, Rhode Island. We will use a combined approach of (1) quantifying the trophic impact of small hydromedusae on the plankton community of Narragansett Bay, Rhode Island and (2) quantifying the functional bases of their feeding and prey selection. Intellectual Merit of the Proposed Activity: The research will lead to new understanding of community feeding rates, prey selection patterns and the underlying feeding mechanisms that have led to the success and evolutionary longevity of the most diverse taxonomic group of medusae. If small medusae feed primarily as omnivores on microplankton and are able to significantly affect microplankton standing stocks, then the research will document a new and important trophic link between the metazoan and microbial food webs. The new knowledge will provide protistan ecologists with enhanced understanding of the factors controlling microplankton standing stocks and production rates. The study will also provide evolutionary ecologists with a greater understanding of the biomechanical factors that have influenced the evolution of small hydromedusan body form and function as well as protist behavior and body form. From this perspective, this study directly addresses the issue of understanding factors influencing biological diversity and its ecological consequences in marine systems, a specific theme emphasized by NSF's Biological Oceanography division. Broader impacts of the Proposed Activity: The project will encourage scientific discovery by documenting a new, but presumably common, trophic link in pelagic food webs. The participation of scientists from two primarily undergraduate institutions and one primarily graduate institution enhances opportunities for training and mentorship. Each institution will involve students in every aspect of the research (5 undergraduates during each year of the proposal, 2 from RWU and 2 from PC; 1 undergraduate from the Marine Biology program at URI will do an independent study course (15 credits) with Gifford during the spring academic term of each project year). Upon receipt of funding, Gifford will apply for a budget supplement to support participation in the project by a secondary school science teacher during the summer months. As in the past, we will use our contacts with media involved in education of the general public (radio, television documentaries, news articles and aquarium exhibits) to communicate our new findings about medusan ecology. Our continuing dialog with these outlets to the public allows us avenues to communicate our findings to a wide public audience and to educate the general public.