This document is the 4th in a series of assessments under the title ‘10 messages for 2010’ and focuses on marine ecosystems. The key messages from this document follow. Marine ecosystems provide key services both globally and locally, which are essential for maintaining life on our planet. However, marine biodiversity faces an unprecedented range of pressures. In recent years, climate change has caused changes in species distribution and presents new challenges for marine biodiversity as oceans become more acidic. Many of the problems faced by marine biodiversity were identified some time ago. European marine biodiversity is primarily protected by establishing Natura 2000 sites under Habitats and Birds directives. There is evidence that marine protected areas support marine biodiversity and fisheries and that extent of recovery increases with the age and size of the protected area. EU governments agree that an ecosystem-based approach is the best means to manage and govern activities affecting the marine environment. Synergies between this marine/maritime framework and well-established marine nature protection policy will benefit European marine biodiversity.