Ecosystems¹are communities of organisms together with their physical environment. They can be of different sizes and can be marine, aquatic, or terrestrial. Broad categories of terrestrial ecosystems are called biomes. In ecosystems, both matter and energy are conserved.Ecosystem classifications²consider all four elements of the definition of ecosystems: a biotic component, an abiotic complex, the interactions between and within them, and the physical space they occupy (ecotope).Types of ecosystems³include:

• Natural ecosystems, which can be biotic (living components) or abiotic (non-living components).
• Aquatic ecosystems, which are located in a body of water.
• Terrestrial ecosystems, which exist on land.