Other experts see more utility in the analysis. One table, for instance, lists specific ecosystem services, and their supposed value, for 11 biomes, or types of natural areas. These include the open ocean, estuaries, seagrass and algae beds, coral reefs, continental shelves, tropical forests, temperate forests, grasslands and rangelands, tidal marshes and mangroves, wetlands and flood plains and lakes and rivers. The next step, Costanza says, is to delineate more clearly the explicit linkages between particular local ecosystems and local economies. But since wetlands perform other services as well, the wetlands' value as a shrimp nursery would be only a minimum indication of their overall value.
Some experts advocate applying traditional economic arrangements to ecosystem services.
For instance, Dr. Graciela Chichilnisky and Dr. Geoffrey Heal, economists at Columbia University, have proposed selling investment shares in a given ecosystem. Using the Catskill watershed as an illustration, they say that the capital thus raised would pay for preserving the watershed. Returns to investors would come either from a share of the costs saved by not having to build a treatment plant or, if the investment were private, by actually selling ecosystem services. In the case of a watershed, clean water would be sold.