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What Do Sea Urchins Eat? Diet Facts & FAQ

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By Lindsey Stanton

sea urchin in sand underwater

Sea urchins are extremely interesting pets that you can keep alone or as part of a larger community. They are also safe to keep in a coral reef tank because they won’t damage it. Many interesting varieties can add quite a bit of color to your aquarium, and they don’t require much space, so you can usually add several to your tank.

One question we get frequently is what exactly urchins eat. If you are thinking about getting one of these colorful pincushions for your saltwater aquarium, keep reading while we look at the different foods they eat in the wild and what you should feed them in captivity to get the maximum life span.

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What Are Sea Urchins?

Sea urchins are spiny globular animals, and you can find more than 900 species on the ocean floor all around the world, including Antarctica. They come in a wide variety of colors with different types of spines. Some will have poison tips to protect them from predators, like the sea otter, starfish, tigerfish, and humans. Some small animals will even hide inside the spikes for protection, while other animals, like some crabs, may carry the urchin in its claw and use it as a weapon. Urchins will usually range from 1 to 4 inches in diameter, but species can grow as large as 14 inches.

sea urchin
Image Credit: Piqsels

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What Do Wild Sea Urchins Eat?

The sea urchin is an omnivore, so it will eat both plants and animal protein. The majority of its diet consists of algae, which is why it makes a good addition to an aquarium, but it also eats plankton and seaweed from rocks and coral reefs. It will also feed on decomposing fish if there is any in its path. Some sea urchins that live in the soft and sandy ground will eat the sand to get at the microorganisms it contains. Other species may have similarly specialized adaptations to their environment.

What Do Sea Urchins Eat in Captivity?

In captivity, your sea urchin will serve the same function as catfish and plecos in freshwater tanks. They eat the algae off the glass, rocks, substrate, and any other surfaces you have in your aquarium. Your sea urchin will also enjoy algae wafers, especially if there are not a lot of algae in the tank. We also like to give our sea urchins a treat of sinking koi food, which is mostly whitefish, and they seem to love it.

We also found that our sea urchins tend to hover near the waterline when there aren’t enough algae in the tank. When this happens, we found that sticking some seaweed between them and the glass will give them a good treat, and they will then go back to the depths of the aquarium.

sea urchin in underwater aquarium
Image Credit: sarangib, Pixabay

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How Do I Feed My Sea Urchin?

Many owners will tell you that you don’t need to feed your sea urchin at all. It should get all of the food it needs scavenging around the tank and eating algae, especially if you have several fish. Fish and other amphibians in the aquarium will leave little bits of food on the floor that the sea urchin will collect. As we mentioned earlier, we noticed our sea urchins staying near the waterline when they cleaned out all of the algae. Sliding some seaweed between them and the glass would cause them to eat it immediately, after which they returned to deeper waters.

If you still think it needs more food, your sea urchin will enjoy algae wafers. You can also indulge its meat-eating side by giving it a small amount of goldfish food or freeze-dried brine shrimp.

sea urchin underwater
Image Credit: Piqsels

How Does My Sea Urchin Eat?

Your sea urchin eats by moving over its food and using its specialized mouth placed at the bottom of the body to collect, grind up and swallow the food. It even has a tongue. As the food travels through the body, it gets digested for nutrients. It expels the waste from the top of the body through the anus.

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As you can see, sea urchins have a more varied diet than you might have expected. However, they require little care once you introduce them to the aquarium and many owners never feed them at all. We feel it’s more fun to give our pets a treat once in a while and the shrimp, wafers, and goldfish food give you plenty for your money.

We hope you have enjoyed this short guide and it has answered your questions. If you have learned something new about your pet, please share this guide to what sea urchins eat on Facebook and Twitter.

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Featured Image Credit: Piqsels

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