Biodiversity in water and on land

SummaryHabitats in the sea, in freshwater, and on land differ dramatically in species composition and diversity. Of the roughly 1.5 million known species of macroscopic organisms on earth, the modern ocean — despite its much larger area and volume — supports only about 15% of species, whereas terrestrial environments account for about 80% of species, and freshwater for the remaining 5% (Figure 1). Even when taking into account previously undetected biodiversity in all of the physical realms revealed through molecular techniques, these differences appear to be robust — certainly among multicellular organisms