Marine Planning
Practical Approaches to Ocean and Coastal Decision-Making


Scientists, agencies and organizations increasingly are using systematic planning approaches to identify where and how to allocate effort in conservation and management, particularly at regional levels. Photo © Mark Godfrey/TNC

Marxan is a decision support tool developed by Ian Ball and Hugh Possingham that is the most widely adopted site selection tool by conservation groups globally. Marxan is a stand-alone software program that provides decision support to teams of conservation planners and local experts identifying efficient areas that combine to satisfy a number of ecological, social and economic objectives. Given data on species, habitats, ecosystems and other biodiversity features, Marxan was designed to minimize the cost of selected sites while meeting all representative goals.

There are many examples of this tool being applied to local and regional planning efforts in over 60 countries around the world. The Marxan decision support tool is designed to provide an objective approach to site prioritization which is adaptable and repeatable, based on a function that evaluates millions of possible alternatives and retains “best” solutions given a stated set of criteria.

Comprehensive, Representative, and Adequate

There are three key aims that Marxan attempts to capture: comprehensiveness, representativeness and adequacy.

A comprehensive selection of high priority conservation sites, for instance, captures every known element of biodiversity. In terms of efficiency the algorithm samples each element and represents each in the final selection process. This approach is based on the representation principle which assumes that our objectives for conservation are to capture viable examples of species, habitats, and ecosystems within a region. Based on this assumption, efficient solutions are sought to meet these aims at the least total cost (and area is often used as a key measure of cost). Adequacy refers to how well the selection process met the representation goal, here primarily a conservation biodiversity objective but can also accommodate other objectives including economic, social or restoration perspectives.


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