Coastal areas are among the most developed and exploited in most regions of the world. Human populations in these areas use the resources from the sea, modify the landscape and produce large amounts of waste and chemical substances, which are released into the marine environment. This extensive use of goods and services from the sea is an indicator of its large contribution to the wealth of human societies. This contribution can be measured in terms of availability of fish, clean water, space, etc., and of desireable services such as recreation, waste disposal and production of food. Production of goods and services in the marine environment is to a large extent based on the large diversity of species of animals and plants and their associated ecological processes. Therefore, to allow continuing use of the resources of the coastal seas, the diversity of species and their associated functions need to be protected and managed in a sustainable way.