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.


3 - 12


Biology, Ecology


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
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.
Leveled by
Selected text level

There are around 300,000 known ocean species. A species is a particular kind of animal or plant. Ocean species are also called marine species.

Most marine species are part of a food chain. A food chain is a top-to-bottom set of animals and plants. They are connected to each other because those on top eat those below. These food chains come together to form a food web.

Level One: Photoautotrophs

The bottom level of the ocean's food chain is made up of tiny living things. These are called phytoplankton. They are so small they cannot be seen without a microscope.

Billions of phytoplankton live in the upper part of the ocean. They take in the sun's light. Through a process called photosynthesis, they turn that light energy into food.

Level Two: Herbivores

The next level of the food chain is made up of plant-eaters. Plant-eaters are known as herbivores. Many are microscopic animals called zooplankton. They drift across the ocean's surface. As they drift, they graze on plants.

There are also larger herbivores. Some examples are turtles and manatees.

Together, herbivores eat a huge amount of plant life. Many end up being eaten themselves. They become food for the carnivorous, or meat-eating, animals. Carnivores make up the food chain's top two levels.

Level Three: Carnivores

The third level of the food chain is made up of small carnivores. It includes fish, such as sardines and herring. These fish eat a great amount of zooplankton. However, they are often eaten, too. They are munched on by bigger fish.

Level Four: Top Predators

Large predators sit at the top of the food chain. They include sea animals, such as sharks, tuna and, dolphins.

Most top predators are very good hunters. They are large and fast.

However, top predators can be eaten too. They are eaten by humans. Some have been nearly wiped put by too much fishing.

The disappearance of top predators can create serious problems. Populations of smaller animals they feed on become too large. These animals then kill off even smaller animals. Or, they eat too much plant life. Then, plant-eating animals no longer have enough food.

Other Food Chains

The main marine food web is based on sunlight and plants. It includes many of the ocean's species. However, it does not include all of them. There are other, separate deep-ocean ecosystems. These depend on chemical energy. This energy enters the ocean through openings in the ocean floor. Such openings are called hydrothermal vents. They release heated minerals from deep within Earth.

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.

Tyson Brown, 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
Clint Parks
Last Updated

October 19, 2023

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.


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


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

Related Resources