The value of the seagrass Posidonia oceanica: A natural capital assessment

•We valued Posidonia oceanica services through ecosystem's ecological performances estimate.•We propose a tool to include hidden costs of natural capital depletion in policies.•Emergy analysis has been applied and a system approach has been followed.•We obtained a monetary estimate of P. oceanica natural capital and its losses.•Appraisals were made about insertion of these estimates in intervention choices.

Making nature's value visible to humans is a key issue for the XXI century and it is crucial to identify and measure natural capital to incorporate benefits or costs of changes in ecosystem services into policy. Emergy analysis, a method able to analyze the overall functioning of a system, was applied to reckon the value of main ecosystem services provided by Posidonia oceanica, a fragile and precious Mediterranean seagrass ecosystem. Estimates, based on calculation of resources employed by nature, resulted in a value of 172 € m−2 a−1. Sediment retained by meadow is most relevant input, composing almost the whole P. oceanica value. Remarks about economic losses arising from meadow regression have been made through a time-comparison of meadow maps. Suggested procedure represents an operative tool to provide a synthetic monetary measure of ecosystem services to be employed when comparing natural capital to human and financial capitals in a substitutability perspective.