Systematic planning shows more than half of the most species-rich ocean region is needed to include all species in representative protected areas

1.The Convention on Biological Diversity Target 3 aims for at least 30% of each marine habitat to be protected by 2030. How much biodiversity will be protected depends on where this 30% is located. The West Pacific region, having the richest marine biodiversity on Earth, is especially important for nature conservation.2.Here, using multiple data-driven measures of the breadth biodiversity, from species to ecosystems from the sea surface to seabed, at a spatial resolution of 0.5° (~55km latitude), we mapped the optimal “Representative Biodiversity Areas” (RBA) for West Pacific countries using decision support software. The measures included surface and near seabed Ecosystems, which were mapped by physical, biochemical and nutrient variables relevant to ecological functioning. Species richness, seagrass, kelp, mangrove, and shallow water coral reef biomes (biological habitats at a local scale) and seabed topographic variation (as rugosity) were also included as complementary measures to maximise representivity of biodiversity overall.3.The 30% RBA generally covered 30% of the Ecosystems, over 77% of the Biomes of seagrass, kelp, mangrove, and shallow water corals, and 60% of physical habitat heterogeneity (topography) and the most species rich areas. Because protecting only these four biomes was not sufficient to include all species, physical habitat heterogeneity and ecosystems should be included in conservation prioritisation because they extend offshore and to all depths.4.To cover the distributions of 80% species in the region, at least 53% of the total area should be under protection.5.Only 25% of the RBA were in MPAs, and < 1% in no-take MPAs. Three countries, Indonesia, Australia and New Zealand, occupied almost half (47%) of the RBA, and 11 countries had more than 30% of their Exclusive Economic Zones in the RBA.6.Opportunities exist to expand and merge existing MPA, increase levels of protection, and having MPA in areas of disputed or shared governance, including 5% of RBA being in the study area’s High Seas. Consideration of the geographically uneven distribution of biodiversity is thus necessary in achieving the 30% by 2030 target. Systematic conservation planning, as shown here, can lead to at least twice as much biodiversity being protected per area. That at least half of the West Pacific Ocean in MPA may be necessary to protect all marine biodiversity, indicates how critical it is to use resources outside MPA in an ecologically sustainable way.