Ecosystems, or communities in which living organisms and nonliving elements interact, fall into two categories: aquatic and terrestrial. Aquatic ecosystems are found in bodies of water, either marine or freshwater. Terrestrial ecosystems are found on land, either forest, desert, grassland or mountain.
Ecosystems, whether aquatic or terrestrial, and their respective subecosystems can be further categorized based on a variety of factors. Among these factors are climate and the type and density of living organisms. Marine aquatic ecosystems characterized by high mineral and salt content include the abyssal plain, polar regions, coral reefs, the deep sea, hydrothermal vents, kelp forests, mangroves, the open ocean, rocky shores, salt marshes and sandy shores. Freshwater aquatic ecosystems include slow moving water (pools, lakes, ponds), fast moving water (streams, rivers) and wetlands.
Terrestrial forest ecosystems characterized by a density of living organisms include evergreen forests, deciduous forests and taiga. Evergreen and deciduous forests are further divided into temperate or tropical, based on climate. Terrestrial desert ecosystems are characterized by low rainfall, extremely high temperatures, low water availability and intense sunlight. Terrestrial grassland ecosystems include tropical savannas and temperate prairies. Terrestrial mountain ecosystems are characterized by a scattered and diverse array of habitats and species of plants and animals.