The location, strength, and mechanisms behind marine biogeographic boundaries of the east coast of North America

range boundaries in these systems (Gaylord and Gaines 2000, Kinlan and Gaines 2003). In the case of marine biogeographic boundaries, the effects of temperature and currents are hard to separate because changes in the ocean circulation are often associated with abrupt changes in temperature. New insights to separate the effects of correlated environmental factors on species distributions can be gained by analyzing the permeability of biogeographic boundaries to species with different characteristics (Wares et al. 2001, Gaines et al. 2009). Species traits that are more likely to be affected by currents can help to distinguish whether currents or temperature could be more important (Wares et al. 2001, Gaines et al. 2009). An important trait that can influence the location, as well as permeability, of boundaries is larval duration. In many marine species that have a pelagic larva in their life cycle, the larvae can be in the water weeks or months; and due to this long larval duration, the distribution of larvae in these species can be affected by currents. Theoretical models demonstrate the potential of ocean currents to create range boundaries by affecting larval transport and the importance of larval duration in determining the fate of populations and the location of range boundaries (Gaylord and Gaines 2000, Byers and Pringle 2006, Gaines et al. 2009). These models, developed for species Ecography 38: 722–731, 2015 doi: 10.1111/ecog.01135 © 2014 The Authors. Ecography © 2014 Nordic Society Oikos Subject Editor: Maria Dornelas. Editor-in-Chief: Miguel Araújo. Accepted 7 October 2014