Erich Horgan, Erica Estrada, Heather Macrellis, Steven Boyd, Shannon McGrath, Larry Madin, Stephen BollensImmunological methods to qualitatively analyze visually unrecognizable gut contents of various invertebrate predators in the marine environment has been successful. In our effort to understand the temporal and spatial impact invertebrate predators have on copepod populations on Georges Bank, polyclonal antibodies were raised against the copepod Calanus finmarchicus, purified, and used to probe for the Calanus epitope in both controlled laboratory experiments with fresh predators, and in formalin and glutaric dialdehyde preserved predators collected from Georges Bank. Our antibody recognizes late naupliar and all copepodite stages of Calanus. Several invertebrate predators found on Georges Bank prey upon Calanus. These include: the hydroid Clytia gracilis, the sandshrimp Crangon septemspinosa, and the hyperid amphipod Themisto gaudichaudii. Using an Elisa-blot method, initial experiments testing the cross reactivity of the primary and secondary antibodies against fresh Clytia, Crangon, and Themisto showed no cross reactivity. In formalin and glutaric dialdehyde (Process 95 cruises) fixed samples, slight cross-reactivity existed. To solve this, a modified primary antibody was prepared by adding predator proteins (toxoid) directly to the primary antibody. In fresh Crangon fed Calanus (n=2), the epitope was detectable throughout the gut with differing relative signal intensities after ingestion, with a maximum signal at 3-4 hours. The Calanus epitope seems to be so stable that we find positive results testing Crangon fecal pellets fed only stage CV Calanus. Crangon fed Calanus (n=2) and placed in 3% formalin for 4 hours test positively for Calanus at up to a 1:1000 dilution. Laboratory testing shows that living Crangon becomes coated with the Calanus epitope under simulated collection conditions and measured copepod densities, as does both 202mm Nitex netting and codend PVC.