Oceans are saltwater ecosystems that account for approximately 71 percent of the Earth's surface. The depth of an ocean may be a mile or more. The landforms characteristic of an ocean may consists of flat sandy bottoms, ravine or cavernous areas; or mountainous or volcano regions. The animal and plant life in the oceans is diverse and, for the most part, is limited to the first few hundred feet in depth. Virtually all living organisms of a saltwater ecosystem can be found within the first few hundred feet. Plant and animal life in the oceans range in size from microscopic organisms to the largest mammals on Earth -- the blue whale.
Estuaries form where freshwater and saltwater mix. These areas are some of the most diverse areas on Earth. The landforms common to an estuary include: rocky or sandy beaches, reefs, marshes, mangrove forests and mud. These landforms support an abundance of plant and animal life that contribute to life-sustaining symbiotic relationships. Plant life of an estuary can include: kelp forests, sea grass and woody swamps. The animal life is also diverse, and can include birds, microscopic organisms, crustaceans, sea reptiles and amphibians.
A coral reef is a collection of living or once-living multiplying coral polyps, upon which marine life live and establish symbiotic relationships with the coral and with other marine life. The landform essential for coral reef growth is a hard rocky surface, that will facilitate anchor. The diverse plant and animal life of the coral reef include those that are hosts to the coral reef and those of which the reef is composed. Some of the animal life include sponges, corals, snails, fishes, invertebrates and other marine life. Seagrass, mangroves and algae compose the plant life.
A saltwater shoreline is an area where the saltwater and the land meet. The landform of a shoreline is composed of a rocky or sandy beach, which is washed by saltwater. This area is an ecosystem, supporting the existence of a specialized group plants and animals. Plant life of a saltwater shoreline can include trees, shrubs, grasses and other ground cover. Saltwater animal life is also very diverse and includes numerous crustaceans.