Defining conservation targets for fish and molluscs in the Port Stephens estuary, Australia using species-area relationships

•The use of species-area relationships to define conservation targets was examined.•Target values were influenced by taxonomic group and modelling assumptions.•Targets based on species-area relationships outperformed uniform habitat targets.•Species-area based targets provided improved species representation in planning.

Effective planning for marine protected areas should be based on conservation targets that are representative of underlying habitats and species distributions. Here, we present the results of an investigation into using species-area relationships (SARs) to define habitat conservation targets for two dominant taxonomic groups (fish and molluscs) using data from the Port Stephens estuary in New South Wales, Australia. Results demonstrated that planning conducted using variable habitat targets, based on SARs, provided significant improvements in representation of habitats and species, compared to planning using uniform (fixed percentage) habitat targets. Planning based on SARs was also found to provide significant improvements in species protection for fish and molluscs when compared with planning implemented without the benefit of detailed biodiversity information. However, SAR targets were found to be sensitive to the function type chosen to represent species distributions (i.e. power-law and exponential), and to the method used for estimation of species richness. Therefore, where SARs are used to set targets in conservation planning, it is important to ensure that they are representative of underlying species distributions. Overall, the improved performance of conservation planning based on SARs indicates the potential for broader application of this technique in planning marine protected areas.