fig. 2.14 > This map shows which marine regions host the highest number of different marine habitats, such as seagrass meadows, coral reefs, estuaries or trenches. The darker the colour of each box, the greater the number of habitats that can be found in that region. The corresponding numerical values have been calculated using a diversity index. Such indexes are applied to compare the biodiversity or habitat diversity of two regions. The two best-known diversity indices are the Shannon-Wiener index used here and the Simpson index. Both take into account the number of species or habitats and their distribution in a given area.

fig. 2.15 > Water temperature and the availability of light and food determine the depth distribution of marine life. Researchers distinguish five depth zones.