also affected by various biophysical parameters (not shown in figure). The translation from ecosystem structure and functions to ecosystem goods and services is given by an ecological production function, and the translation from ecosystem goods and services to value is given by an economic valuation function. There may be occasions in which the structure of the ecosystem is valued directly by humans, without the intermediation of functions, goods, or services. For example, people may value the existence of redwood forests in their own right rather than because of any functions, goods, or services that they might provide; a possibility indicated in Figure 1-3 by the direct connection from ecosystem structure to values (also given by an economic valuation function). Estimating the value of ecosystem services requires uncovering both the ecological production function and the economic valuation function. As Chapters 3, 4, and 5 illustrate, uncovering each of these functions is difficult. Furthermore, because aquatic ecosystems are complex, the production of goods and services can be complicated and indirect; this in turn makes the translation from ecosystem structure and function to ecosystem goods and services difficult. The lack of markets and market prices and of other direct behavioral links to underlying values makes the translation from quantities of goods and services to value difficult as well.