Salps are pelagic, barrel-shaped, jet-propelled swimmers that have higher filtering rates of small particles (1 m- 1 mm) than almost any other planktonic grazer. The majority of salp species are found in oceanic tropical and subtropical waters where they play a critical role in cycling of organic material. An understanding of their swimming behavior and filter feeding mechanics is critical to teasing out the ecological roles of these important grazers. The coupling of feeding and locomotion by salps during jet propulsion results in trade-offs between these two life processes. This group of animals is characterized by a diversity of morphology and swimming behaviors, that likely relate to ecological roles of co-occuring species. Preliminary data indicate that morphological differences may account for a range of lifestyles among salps from fast swimming forms to slower swimming forms. Fast swimming salps are characterized by enhanced musculature, higher pulse rates and linear, streamlined chain structures compared to slower, surface oriented salps.
This study will examine the swimming and feeding behavior of salp species present off the Pacific Coast of Panama and use this information to draw linkages between morphology, swimming mechanics and ecological roles. The approach will combine field and laboratory methods that span scales from the microscopic filtering apparatus to the flow field around the animal. The work will focus on Salpa cylindrica, a fast-swimming, streamlined form, Pegea confoederata, a slower swimming form and Cyclosalpa spp., a slow swimming form with wheel shaped aggregates. The specific goals of this project are to a) quantify the flow of water produced by swimming salps in the field and in the lab and examine the connection between flow and feeding efficiency, b) describe the form and movement of the entire filtering mesh with 3-dimensional video and, c) measure filtering mesh parameters microscopically in order to describe the small-scale mechanics of filtration. There is increasing knowledge of the substantial transport of material to the ocean's deep interior by gelatinous grazers but we lack information about the ecological function and relationships of individual species. The application of new techniques will provide a mechanistic basis for variations in filtering rates and particle retention efficiencies among salp species. This work will enhance our understanding of the evolutionary diversity of form present in salps and how it relates more broadly to the coexistence of other planktonic grazers.
Broader impacts of the proposed work include the training of one graduate student (Ph.D.) and two undergraduate students. The graduate student will develop skills in microscopy, fluid mechanics and methods for working with fragile planktonic organisms. Undergraduate students will gain research experience both in the field and the laboratory. The study of large gelatinous fauna in a pristine setting will be appealing to the public and we have already contacted the editors of WHOI's Oceanus magazine about publishing our findings. The online version of the magazine receives 30,000 hits each month and 6,500 print copies of each issue are distributed.
