The resolution of structure and function within pelagic food webs requires the use of appropriate techniques and equipment. Gelatinous zooplankton are targeted in this proposal as they represent a poorly studied but ecologically important fauna throughout the oceanic water column. Due to their delicate nature, the metabolism of most soft-bodied zooplankton can only be investigated in their natural environment and it is hypothesized that in situ measurements of oxygen consumption will lead to reduced errors associated with animal handling, pressure and temperature changes, and light shock. Data obtained in situ will be used to quantify the contribution of gelatinous zooplankton to the energetics of midwater communities. Furthermore, comparisons of this information with similar metabolic data on crustaceans and fishes will provide an important counterpoint and permit a better understanding of selective pressures in the deep sea.