We used Marxan as the conservation planning software. This approach allows planners to create both a horizontal and a vertical zoning of management actions while still following the core principles of systematic conservation planning. It enables planners to account for depth-related variability in biodiversity, human activities, threats to biodiversity, environmental conditions and the cost of conservation actions.
The key modification enabling this is the creation of 3D planning units, with x, y and z dimensions (Fig 1). This means planning units can potentially share boundaries with other planning units that are next to them but also above or below.
Given that Marxan attempts to minimize the boundary of the resulting network of selected planning units (see Decision Point #62), we can use the 3D adjacency of planning units to integrate the third dimension into Marxan. Moreover, having 3D planning units enabled us to stratify the water column into different layers, allowing planners to account for biodiversity, threats, and cost of conservation actions, at different depths. It makes sense in theory but how does it work in practice? We tested our new approach using the entire Mediterranean Sea as a case study. This involved developing a conservation plan which involved choosing sites where at least 20% of the distribution (accounted for in cubic kilometres) of over 1000 conservation features was represented.
The results from our case study showed that it was possible to achieve configurations of chosen 3D planning units in which the targets for all the conservation features were achieved. More importantly, we demonstrated that through this new approach, in some areas of the ocean, not all the planning units available along the water column were selected for conservation.
Created with images by Johnny Chen - "Fish near the sea bottom" • joakant - "swarm fish meeresbewohner fish swarm underwater blue" • Skitterphoto - "tropical aquarium fish"