Marine plants and animals live in an environment where chemical signals are often more important than visual signals. Waterborne chemicals provide marine organisms with critical information about the quality of their environment and the location of food, predators, and mates. However, when the tide is out, intertidal plants and animals spend large amounts of time exposed to air, where waterborne chemical signals are unavailable but airborne chemical signals may be important. Preliminary data has shown that when they are being consumed by grazers, some intertidal plants release dimethyl sulfide, an airborne chemical that can cause nearby plants to produce additional defenses against grazers. This use of airborne signaling chemicals by marine plants is a new and potentially important mechanism of communication among marine intertidal organisms. Because dimethyl sulfide can be detected by animals, it may serve as a signal to other grazers and to their predators about the presence of food or enemies. Thus, the release of dimethyl sulfide has the potential to affect interactions throughout marine food webs. This project will use biochemical methods to measure the release of dimethyl sulfide by marine plants under a variety of environmental conditions and its subsequent movement throughout the environment. A variety of behavioral, physiological, and ecological assays will then be used to determine the effects of airborne dimethyl sulfide on defensive responses and growth rates of nearby plants as well as the responses and feeding rates of herbivores and predators. The results of this study will provide fundamental information about how marine food webs function. Because dimethyl sulfide is important in the global cycling of sulfur, this study will also contribute to knowledge of sulfur movement from the oceans to the atmosphere. At least eight undergraduate students will help conduct this work; therefore, the project will contribute to the training of the next generation of marine scientists.