Species diversity
In the same way as on land, there are also many types of ecosystem in the ocean. Some are rich in species, such as kelp forests along the coast or cold-water coral reefs. These areas are important habitats for marine organisms during juvenile development and growth.=====   Many marine species are also associated with more than one type of ecosystem; some live partly on the bottom and also spend parts of their lives in open waters.

Biological production in the ocean varies from place to place, and through the year. During spring and summer, a rich supply of nutrients together with increasing day length and temperature lead to high primary production in phytoplankton. They are an important link between chemical and biological processes in the ocean; as primary producers they transform water and carbon dioxide into oxygen and glucose. Phytoplankton is food for several groups of zooplankton, which in turn are eaten by organisms on higher levels in the food web such as pelagic fish.

Resource diversity
The ocean has always been a very important resource for Norway. Along the coast, settlements depended on fisheries. Stockfish, and later also clipfish, have been important in exportation. Today, many marine species are commercially exploited and fish is the second most important export article (only preceded by oil). Ocean areas are therefore very important to the Norwegian economy. Important features of the cultural heritage and identity are also associated with the marine environment and marine species.

Environment and ecosystem
On earth, factors such as temperature, wind and humidity can display high local variation. In the ocean, on the other hand, these environmental variables are relatively stable over wide areas. As a result, many marine species can potentially move over large geographical areas before they encounter climatic spreading barriers.

This relatively uniform environment also affects marine biodiversity, and many marine ecosystem types have a more limited biodiversity than terrestrial ecosystem types. Marine food webs in general have more levels than terrestrial food webs. At the same time, they also spread over large geographic areas due to migration or transfer by ocean currents. Many organisms also have a life cycle were different stages are associated with different types of ecosystem, geographic areas and depths, in turn linking these environments together.