The effects of off-road vehicles (ORVs) on invertebrates inhabiting macrophyte debris (wrack) and supratidal sands on energetic beaches in the northeastern United States were studied at Cape Cod (MA) and Fire Island (NY) National Seashores. the authors focus on the effects of off-road vehicles on the supratidal invertebrates. First, they compare four different wrack-laden beaches in the northeastern U.S. (three within Cape Cod National Seashore, one within Fire Island National Seashore) that have neighboring sections of ORV-traveled and ORV-free beach and second, the authors perform a controlled direct-impact study, in which we drive over colonized, experimental wrack clumps near Ballston Beach, MA, to assess the effects. By replicating their sampling at four beaches and using several sampling methods, the authors strove to maximize the chances that observed differences between treatment (traffic) and control (non-traffic) sites were due to ORV activity. In the manipulative experiment, the authors controlled the level and timing of the traffic that the wrack-associated species received. In addition, the authors compared accompanying environmental variables that may be good indicators of the effect of traffic on invertebrate habitat.