A practical approach to setting heuristic marine biodiversity targets for systematic conservation planning

Abstract

Systematic conservation plans are proliferating as countries work towards identifying priorities for meeting international conservation commitments. These analyses generally require targets for input biodiversity features, which can be difficult to set quantitatively and defensibly. We aimed to develop a robust, heuristic approach for setting biodiversity targets for marine systematic conservation planning (SCP). From the literature, we distilled principles for increasing and decreasing a baseline biodiversity target, and identified recommended target amounts for the baseline targets and adjustments. These heuristic rules were tested in a systematic plan, run in Marxan, by using them to set targets for 976 marine biodiversity features from South Africa. Marxan outputs were compared with those from alternative scenarios that had: area-weighted targets (as an alternate heuristic); commonly used fixed targets of 10 %, 30 %, and 50 % (as planners align to Aichi Target 11, 30 × 30, and Nature Needs Half, respectively), and random targets. Both scenarios with heuristic targets (our heuristics, and area-weighted) passed the target sensitivity test and outperformed the scenarios with fixed targets in terms of feature representation for a given area and cost. This was better achieved using our heuristic targets, which had generally significantly higher feature representation in a more efficient design than all other scenarios. Our approach for systematically setting heuristic biodiversity targets can be widely applied, and although developed for marine planning, is expected to perform just as well for land-based planning. The rules and target amounts are not prescriptive but serve as a useful guide that can be adapted to other contexts.