During the winter, Trichechus manatus latirostris (Florida Manatee) depends on long periods of rest in comparatively warm thermal refuges to help conserve energy and maintain stable body temperatures. Pterygoplichthys disjunctivus (Vermiculated Suckermouth Sailfin Catfish) has been observed attached to, and grazing algae from, Florida Manatee in Volusia Blue Spring. We hypothesized that the disturbance caused by grazing armored catfish would significantly alter Florida Manatee behavior. Analyses of 6 hours of underwater video of Florida Manatee behavior, with and without attached armored catfish, revealed that during each observation period, Florida Manatees with attached catfish demonstrated significantly higher activity levels and numbers of active behaviors. Increased Florida Manatee activity caused by the armored catfish may compound the impact of other known threat effects.