Cunningham 9808267 This project investigates the impact of the powerful 1997 El Nino Southern Oscillation Event on coastal marine organisms. During E.N.S.O. years, the ocean current that normally brings cold water south along the Western United States changes direction. This change in direction not only reverses the direction of flow, but raises sea surface temperatures far beyond normal. During E.N.S.O. years, many marine organisms are found far to the north of their normal geographic ranges. In this project, we are asking whether E.N.S.O. events have an effect on the genetic population structure of the common acorn barnacle Balanus glandula. Previous work has shown that barnacles collected to the south of Monterey Bay have a characteristic genetic signature. We will be asking if the proportion of southern individuals north of Monterey increases as a result of the northward flowing current. This project is important because the warmer conditions of E.N.S.O. years provide a window onto the consequences of global warming on the geographic ranges of marine species. These studies can help identify which species will benefit, and which ones will be hurt by global warming. This study takes the unique perspective of studying the effects of warming trends on the genetics within species. This is especially useful, because genetics can provide information about past distribution and dispersal patterns.