With increasing global concern over marine biodiversity loss, defining Marine Protected Areas (MPAs) – regions where human activity is limited to allow marine ecosystems to thrive – is simple and appealing. But the health of marine ecosystems continues to decline, even as the total area of MPAs around the world is increasing. Why aren’t MPAs helping? It turns out that the places where biodiversity is under the most pressure are also the places humanity is most reluctant to relinquish, due to their social or economic value. Dr Piers Dunstan of CSIRO will give us the What (is happening), Why (isn’t it working), Where (should they be) and How (do we fix this) of MPAs.