Wetland Migration Barrier (image) Virginia Institute of Marine Science Share Print E-Mail Caption U.S. coastal wetlands generally lack dikes or levees, allowing marshes to migrate landward into coastal forests. Credit © Dr. Matt Kirwan/Virginia Institute of Marine Science. Usage Restrictions One-time use only. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.