Which Ocean Has the Most Marine Life?

By MarEx 2014-05-20 20:10:00

Emily Tripp, marine scientist and commentator, answers the question: Which world oceans have the most marine life?

Short Answer: It’s complicated because there really are no concrete borders between oceans. But if we had to pick, it would probably be the Pacific because it’s the largest and contains the most coral reefs.

Long Answer: It’s easier to determine where the most life is by separating the oceans into different zones. The pelagic zone contains everything except for the coast and the sea floor and is divided into five parts. The epipelagic zone extends from the surface to 200m down. It receives plenty of sunlight and therefore contains the most biodiversity in the ocean. Next comes the mesopelagic zone which extends from 200m to 1,000m. It is also called the twilight zone because of the limited light that can filter through these waters. It is too dark for photosynthesis so life in this area is limited. 

The bathypelagic zone extends from 1,000m to 4,000m and receives no sunlight at all. (Sperm whales can reach this zone in search of food.) The only light here comes from some organisms that can produce their own light. The abyssopelagic (or abyssal) zone continues to 6,000m where very few creatures can be found due to the lack of light and near freezing temperatures. The deepest a fish was ever found was here in the abyss at 8,372m down. Finally, the hadalpelagic zone extends from 6,000m to the very deepest parts of the ocean in deep trenches and canyons. Some starfish, tube worms and other invertebrates can be found way down here.

Long Answer: Check out the following facts about our oceans!

Pacific Ocean

The largest ocean covers nearly a third of the planet and contains 135,663 km of coastline.
It is home to the deepest point in the world, the Challenger Deep in the Mariana Trench.
It has largest number of coral reefs. There are typically about twice as many coral species in Pacific Ocean reefs as in Atlantic Ocean reefs. More than 70 per cent of the world’s fish catch comes from the Pacific Ocean.

Atlantic Ocean

The second largest ocean covers about a fifth of the planet and contains 111,866 km of coastline. The North Atlantic is the saltiest area in all the oceans. About 20 per cent of the global fish catch comes from the Atlantic Ocean.

Indian Ocean

The third largest ocean contains 66,526 km of coastline. It is the world’s warmest ocean and has a fairly low oxygen content. A little over 8 per cent of the global fish catch comes from the Indian Ocean.

Southern Ocean

The fourth largest ocean is comprised of the southern most parts of the Pacific, Atlantic and Indian Oceans. It is home to 17 species of penguins. It contains 17,968 km of coastline. Less than one per cent of the global fish catch comes from the Southern Ocean, although many fisheries here are completely unregulated and unreported.

Arctic Ocean

The smallest of the five oceans is also the most extreme and least explored. It contains 45,389 km of coastline. There are 400 known fish species living in Arctic seas and adjacent waters, most living on or near the bottom.

So, based on global fisheries and the overall biodiversity of coral reef ecosystems, the Pacific Ocean wins for most marine life.

Emily Tripp is the publisher and editor of MarineScienceToday.com, an online magazine about what's in, on, and around the oceans. She holds marine science and biology degrees from the University of Miami's Rosenstiel School of Marine and Atmospheric Science.

Photo credit: NOAA