Contemplating the Coasts

show/hide words to know

Productive: getting a lot done or providing a favorable environment with food and shelter for many organisms to grow.

Upwelling: when seawater rises, usually forcing cold water from the bottom of the ocean to the surface. This is often due to the movement of deep ocean currents.

A Sea of Plenty

Coral reef at Jarvis Island

Shallow tropical seas allow living coral to grow and cover the bottom of the coastal biome. Click for more detail.

At the coast, land meets sea, fresh water meets salt water, and light trickles to the ocean floor. Because of this mixed meeting of different factors, the coast is very productive.

This means these seas have plenty of food, light, and nutrients to feed many types of organisms.

The coastal biome has two fairly well defined borders: the high water line near on the shore, and the steep edge of the underwater continental shelf far offshore.

Continental shelf

Coasts are found on the continental shelves. Click for more detail.

The border on shore is the intertidal zone, or the area that is sometimes exposed to the air during low tide. These tides flood and recede on a roughly 12-hour cycle because the gravity of the moon pushes ocean water around the planet.

Past the underwater continental shelf the water quickly becomes too deep for light to reach the bottom, so fewer organisms live there. Between these boundaries many creatures build their homes, which can be in coral reefs, oyster beds, kelp forests, sea grass meadows, or soft sandy habitats.

Flowing Waters

Whenever it rains on land, the fresh water flows downhill creating streams. These streams meet and create bigger and bigger rivers until they get to the sea.

If you've been to a large river, like the Mississippi, you know that river water isn't always clear. By the time fresh river water reaches the ocean, it has picked up dirt, silt, and minerals. This water often brings important nutrients to the tiny organisms living in the salty ocean water.

Mississippi River Delta

Many rivers lead to the ocean, like the Mississippi, shown here. Click for more detail

On the seaward side of the coastal biome, far away from shore and its rivers of fresh water, ocean currents carry more nutrients to the coast. These currents bring nutrients from the bottom of the ocean up to the coastal shelf where sun-loving organisms can use it for food. The movement of these nutrient-rich currents is called upwelling.

Under the Sun

The last piece of the productivity puzzle is sunlight. Even under water, sunlight is important for plants and animals to survive. Because sunlight shines through shallow coastal waters, this area is home to algae and phytoplankton. These organisms can use light and nutrients to make their own food. Algae and plankton then become food for larger animals like fish, clams, corals, whales, sharks, sea turtles, and even seabirds. More than half of the species on the planet live in the marine biome. Because of how productive coastal waters are, the coastal biome is home to a huge portion of these marine species.

Additional images via Wikimedia Commons. Gasflame nudibranch by Seascapeza.

View Citation

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Bibliographic details:

  • Article: Anatomy of the Coast
  • Author(s): Robert Wildermuth
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: November 17, 2014
  • Date accessed: July 16, 2024
  • Link:

APA Style

Robert Wildermuth. (2014, November 17). Anatomy of the Coast. ASU - Ask A Biologist. Retrieved July 16, 2024 from

American Psychological Association. For more info, see

Chicago Manual of Style

Robert Wildermuth. "Anatomy of the Coast". ASU - Ask A Biologist. 17 November, 2014.

MLA 2017 Style

Robert Wildermuth. "Anatomy of the Coast". ASU - Ask A Biologist. 17 Nov 2014. ASU - Ask A Biologist, Web. 16 Jul 2024.

Modern Language Association, 7th Ed. For more info, see
Gasflame nudibranch

Some animals, like many nudibranchs, can live in shallow coastal waters or in deeper waters of the ocean.

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