Below surface is permafrost, frozen all year. Lichen, grasses, andsmall shrubs dominate. It consists of the following recognized habitats. Estuaries -Regions where fresh water enters the marine habitat,sometimes used to describe collectively any body of water surrounded by landwith open connection to sea water. There is a wide range of salinites, depending on tides and wate flow.
Estuaries are nutrient rich and very fertile.
They serve as the breeding ground for many invertebrates and somefish. The benthic zone is the bottom of the marine habitat. The zone in which enough sunlight penetrates for photosynthesis to occur is called the euphotic zone, usually about 200 meters deep. This is the least productive of marine habitats, due to lack of nutrients and verysmall planktonic organisms in warmer waters. At high temperatures the amount of oxygen produced by the symbiotic photosynthetic organisms becomes toxic to the coral animals.