Most marine ecosystems present priorities for conservation which are different from, but no less urgent than, those of terrestrial systems. These priorities relate to understanding and regulating human use and impact within the large scale, and the high but variable degree of connectivity of marine systems. The identification and preservation of remnant examples of marine ecosystems, otherwise destroyed by human activity, is generally less of an issue than it is for terrestrial conservation. As a consequence, the needs of marine conservation are not readily addressed by models developed for terrestrial ecosystems, which are based on excluding or severely limiting human access in managed areas. An exception is the philosophy of the Biosphere Reserve, developed as part of the UNESCO Man and the Biosphere Programme. This appears particularly appropriate to marine environments, as it focuses on managing human activities and impacts within the sustainable capacity of the ecosystem. © 1990, Foundation for Environmental Conservation. All rights reserved.