ABSTRACT

Several studies have found that medusan predation plays a dominant role in a variety of marine planktonic communities, but the variables controlling medusan prey selection and ingestion rates remain contentious. A possible reason for this lack of consensus is that there is not a strong mechanistic understanding of medusan predation and, rather than a single uniform type, medusae are a diverse phylogenetic, morphological and functional array of predators whose mechanical differences must be understood before realistic predator models can be constructed. This study will examine the hypothesis that the diversity of functional alternatives are constrained to two major mechanical solutions for medusan motility: jetting and rowing propulsion. The investigators argue that these propulsion types are the key to understanding predation patterns because propulsive mode is directly related to foraging mode. However, this presents a major challenge because only jet propulsion has been quantitatively described in medusae. In contrast, all of the documented examples of planktonic standing stock limitation by medusae involve rowing-propelled, cruising medusae that feed by fluid entrainment of prey during swimming. The investigators contend that quantification of fluid interactions with medusan prey capture surfaces is a necessary prerequisite to the construction of realistic models predicting medusan prey selection and ingestion rates. The first goal of the project is to quantitatively delineate hydrodynamic characteristics of rowing and jetting propulsion. This will involve an interdisciplinary comparative study of representative members of major medusan lineages using DPIV measurements of free-swimming animals and newly developed methods for the analysis and interpretation of these quantitative flow visualizations. From these results, the investigators will deduce appropriate hydrodynamic models for application to major medusan lineages. The second major goal is to quantitatively describe the interactions between fluid flows and capture surfaces of the most ecologically influential medusan lineages - the rowing-propelled, cruising foragers. Members of this group include various lineages that capture prey in either the upstream (e.g. Narcomedusae, Coronatae) or downstream (e.g. Leptomedusae, Semastomeae, Rhizostomeae) components of flow around the swimming bell. This research will detail the fluid flow rates past capture surfaces and will serve as the basis for hydrodynamically-based clearance rate estimates of medusan predation.
Intellectual Merit of the Proposed Activity: Medusan predation affects all planktonic groups, and development of a hydrodynamically based understanding of medusan predation will have potentially wide application to studies of other planktonic taxa. Additionally, this information will contribute novel conceptual insights to the fields of animal swimming and integrated marine animal behavior. 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. Furthermore, the elucidation of governing design principles in marine locomotion can complement existing studies of underwater vehicle design inspired by fish swimming.
Broader impacts of the Proposed Activity: Students, primarily undergraduates, will participate in every aspect of the proposed research and the investigators will participate in programs designed to direct these opportunities for training and mentorship toward underrepresented undergraduate students. Two of the principal investigators participating in this collaboration are from primarily undergraduate institutions and one is from a primarily graduate institution. The participation of underrepresented undergraduate students will be encouraged through established programs at Caltech aimed at providing research opportunities to minority students from other campuses across the country. The Caltech investigator will also continue in his role as Coordinator of the Freshmen Summer Institute (FSI) Research Program at Caltech. This annual, four-week program was initiated in 2001 in response to the disproportionately low number of students from underrepresented groups participating in research activities on campus. In addition, they will use their contacts with media involved in education of the general public to communicate our new findings about medusan form and function. Finally, an online tutorial will be developed to disseminate the new experimental DPIV methods to other research groups investigating various topics in aquatic biomechanics and marine ecology.

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