Marine Food Chain

Marine Food Chain

The marine ecosystem is made up of a complicated series interconnected energy producers—like plants and photoplankton—and consumers—from plant-eaters to meat-eaters, both great and small.

Grades

3 - 10

Subjects

Biology, Ecology

Image

Dugong Feeding on Seagrass

As herbivores, dugong and their manatee cousins occupy the second level of the marine food chain. Here, a dugong feeds on seagrass in the Red Sea.

Photograph by Adam Suto
Leveled by
Newsela
Selected text level


It's a Fish-Eat-Fish World

Some 300,000 marine species are known to science—about 15 percent of all the species identified on the planet. But the sea is so vast that a million or more as yet unknown species may live in its waters. Most of these aquatic species are tied together through the food web.

Level One: Photoautotrophs

The foundation of the sea's food chain is largely invisible. Countless billions of one-celled organisms, called phytoplankton, saturate sunlit upper-ocean waters worldwide. These tiny plants and bacteria capture the sun's energy and, through photosynthesis, convert nutrients and carbon dioxide into organic compounds. On the coast, seaweed, and seagrasses do the same thing.

Together, these humble plants play a large role: They are the primary producers of the organic carbon that all animals in the ocean food web need to survive. They also produce more than half of the oxygen that we breathe on Earth.

Level Two: Herbivores

The next level of the marine food chain is made up of animals that feast on the sea's abundant plant life. On the ocean's surface waters, microscopic animals—zooplankton, which include jellyfish and the larval stages of some fish, barnacles, and mollusks—drift across the sea, grazing opportunistically. Larger herbivores include surgeonfish, parrotfish, green turtles, and manatees.

Despite their differences in size, herbivores share a voracious appetite for ocean vegetation. Many of them also share the same fate—which is to become food for the carnivorous animals of the food chain's top two levels.

Level Three: Carnivores

The zooplankton of level two sustain a large and diverse group of small carnivores, such as sardines, herring, and menhaden. This level of the food chain also includes larger animals, such as octopuses (which feed on crabs and lobsters) and many fish (which feed on small invertebrates that live near shore). Though these animals are very successful hunters, they often fall prey to a simple fact of ocean life: Big fish eat smaller fish.

Level Four: Top Predators

The large predators that sit atop the marine food chain are a diverse group that includes finned (sharks, tuna, dolphins), feathered (pelicans, penguins), and flippered (seals, walruses) animals. These apex predators tend to be large, fast, and very good at catching prey. They are also long-lived and usually reproduce slowly.

But the marine food chain's top predators are common prey for the most deadly hunters of all—humans. When top predator species are depleted, their numbers are often slow to rebound, and their loss can send shock waves through the entire food web.

Alternative Food Chains

The primary marine food web, which is based on plant productivity, includes many of the sea's species—but not all of them. There are other deep-ocean ecosystems that are entirely independent of the sunlight energy that kick-starts the main marine ecosystem. At their roots, these unique ecosystems are fueled by chemical energy, which enters the ocean from sources like seafloor hydrothermal vents.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Director
Tyson Brown, National Geographic Society
Author
National Geographic Society, National Geographic Society
Production Managers
Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society
Program Specialists
Sarah Appleton, National Geographic Society, National Geographic Society
Margot Willis, National Geographic Society
Producer
Clint Parks,
other
Last Updated

June 2, 2022

For information on user permissions, please read our Terms of Service. If you have questions about licensing content on this page, please contact ngimagecollection@natgeo.com for more information and to obtain a license. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. She or he will best know the preferred format. When you reach out to him or her, you will need the page title, URL, and the date you accessed the resource.

Media

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text

Text on this page is printable and can be used according to our Terms of Service.

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources