Introduction

The ecosystem services assessed in Part III are large-scale; some of them are planetary in nature and provide human benefits through the normal functioning of the natural systems in the ocean, without human intervention. This makes them intrinsically difficult to value. However, some of these same ecosystem services in turn sustain provisioning services that generate human benefits through the active intervention of humans. This is the case, for example, for the global ecosystem service provided by primary production by marine plants, which by synthesizing organic matter from CO2 and water, provide the base of nearly all food chains in the ocean (except the chemosynthetic ones), and provide the food for animal consumers that in turn sustain important provisioning ecosystem services from which humans benefit, such as fisheries.

The services in Part III are not the only ones provided by the ocean. Many other ecosystem services are directly or indirectly referred to in Parts IV to VI of this Assessment. The provisioning ecosystem services related to food security are addressed in Part IV, Assessment of Cross-Cutting Issues: Food Security And Food Safety (Chapters 10 through 16); those related to coastal protection are referred to in Part VI, Assessment of Marine Biological Diversity and Habitats, in Warm Water Corals (Chapter 43), Mangroves (Chapter 48), and in Aquaculture (Chapter 12), Estuaries and Deltas (Chapter 44), Kelp Forests and Seagrass Meadows (Chapter 47) and Salt Marshes (Chapter 49); the maintenance of special habitats are addressed in Chapters on Open Ocean Deep-sea Biomass (Chapter 36F); Cold Water Corals (Chapter 42) and Warm Water Corals (Chapter 43), Hydrothermal Vents and Cold Seeps (Chapter 45), High-Latitude Ice (46) and Seamounts and Other Submarine Geological Features Potentially Threatened by Disturbance (Chapter 51); the sequestration of carbon in coastal sediments, the so-called blue carbon, is addressed in Chapters on Mangroves (Chapter 48), Estuaries and Deltas (Chapter 44) and Salt Marshes (Chapter 49); the cycling of nutrients is covered in Estuaries and Deltas (Chapter 44) and Salt Marshes (Chapter 49, but also Chapter 6).

Because of the very large scale of the services analysed in Part III, although they are influenced by human activities, they cannot be easily managed, and in certain cases they cannot be managed at all.