The Biology of Gelatinous Zooplankton: Investigations on the Trophic Relationships of Salpa thompsoni and Salpa gerlachei in the Southern Ocean

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Two species of salps, Salpa thompsoni and S. gerlachei, occur in the Southern Ocean near the Antarctic Peninsula. Both are known to form immense blooms that almost entirely dominate the biomass. A knowledge of the biology of these species is essential to understand the trophic relationships and global processes that occur in the Southern Ocean. This project will investigate the feeding rates, defecation rates, assimilation efficiency, growth, reproduction and metabolism of both species, in order to develop an energy budget. The behavior of salps will be studied in the field, and laboratory experiments will incorporate these field observations. Feeding rates will be measured both in the laboratory and in the field, and the results will be compared. Growth, reproduction and metabolism will be measured in the laboratory. In addition, the hyperiid amphipod parasites of salps will be examined using a combination of field and laboratory methods. The potential effect of these parasites on the growth and reproduction of salps will also be considered. Several species of Antarctic fish will be observed in the laboratory to study predation on salps and other gelatinous zooplankton. A number of fish that occur near Palmer Station feed heavily on salps. Fish will be fed known quantities of gelatinous prey, and digestion rates will be determined. These studies will assess the ability to identify and quantify the remains of gelatinous organisms with gut content analyses. These studies will provide important data on the trophic position of salps in the Southern Ocean, both as consumers of phytoplankton and as prey of other organisms. These studies are an essential prelude to further studies on recruitment and population structure in Southern Ocean planktonic communities. In addition, the research proposed herein will provide basic information on the ways in which oceanic zooplankton cope with the seasonally variable food resources of the Southern Ocean.