I remember snorkeling off of Panama City Beach, Florida as a kid and finding starfish and sand dollars in the water. These incredible creatures have fascinated me ever since, though I had no idea people could have them as pets.
In recent years, though, as I’ve delved more deeply into marine tank fishkeeping, I’ve learned heaps on these critters and discovered that sea stars not only are beautiful creatures of the sea, but they make for fascinating pets.
To help newer sea star keepers, I thought we’d look into some questions like what do crown of thorns starfish eat or what do chocolate chip starfish eat? Or generally, what do starfish eat? We’ll take a deep dive into all things starfishes diet!
Background on Starfish
Starfish belong to the Echinoderms class of creatures, which is a large group of marine-only animals. This class means they have symmetrical limbs around a single central point, have tube feet and no head, and a flat body.
Total, there are about 7,000 species of Echinoderms. These include sand dollars, sea urchins, sea cucumbers, crinoids, brittle stars, and starfish or sea stars. These creatures are not technically fish, so sea star is kind of more accurate.
Sea stars use sea water instead of blood to circulate the nutrients in their bodies. They have no scales, gills, or fins, but use tiny tube feet to move around. These tiny feet are on the undersides of their bodies, with up to 15,000 of them allowing them to move as quickly as nine feet every minute.
Specifically, sea stars belong to the Asteroidea class, which is derived from the words in Greek meaning “aster” and “form,” since they kind of look like aster flowers. Most species have 5 radial arms, but some species can have as many as 40 arms. They may regrow these arms if they are damages and they may actually intentionally shed limbs to free themselves from danger or are subjected to high temperatures for too long.
They may grow up to 9.4-inches long and the largest species can weigh up to 11 pounds. They have eye spots on each arm that are sensitive to light.
On average, they live between 5 and 35 years, depending on the species, environment, and level of care.
These unique creatures have been eluding our knowledge for years. It was only finally in 2013 that scientists finally came to understand how starfish feed. Let’s take a look.
How Do Starfish Eat?
In 2013, a brief was released by scientists upon their discovery of how starfish eat. “Scientists have identified a molecule that enables starfish to carry out one of the most remarkable forms of feeding in the natural world. A starfish feeds by first extending its stomach out of its mouth and over the digestible parts of its prey, such as mussels and clams. The prey tissue is partially digested externally before the soup-like ‘chowder’ produced is drawn back into its 10 digestive glands.”
They don’t have visible mouths, so it’s not terribly surprising it took scientists many years to discover this eating process. Their mouths and stomachs – they have 2, including the one they extend outward to get the food – are on the undersides of their bodies, however, and their arms allow to the feel around for their food. Movement is a big key to their success in eating, as movement allows them to discover viable food options.
This video gives you an idea of how they move.
Their arms also allow them to grab onto and hold their food, pry shells on mollusks apart, etc.
Once they have absorbed the food, they draw the stomach (called the cardiac stomach) back into the body where they then digest the food with the second stomach (called the pyloric stomach). This process enables them to eat things that are larger than their stomachs.
To witness this strange and incredible process, you can check out a video from Vancouver Aquarium.
What Do Starfish Eat in the Ocean?
Just like different fish species eat different food types, starfish species vary in their diets. Some are scavengers, some eat similarly to fish, and some are predators. Most species are carnivores and feed on mollusks like clams and oysters. A single sea star in the wild can eat over 50 clams in a single week.
Other things they eat in the wild include:
- Hermit crabs
- Decomposed organic material
- Coral polyps
- Other starfish
- Sea snails
- Sea urchins
- Slow-moving fish
- Sea cucumbers
- Fish eggs
- Sand dollars
- Other crustaceans
What Do Starfish Eat in Aquariums?
Pet starfishes diet will obviously vary from that in the wild, as it is a closed system that you, the owner, must develop. They typically need to be fed every 2-3 days and they should not be kept by beginners. They are complicated and require advanced care.
You’ll find it’s easy to tell if your starfish is hungry. Simply place a piece of food where it can access quickly and easily and it will gobble it down in short order. How to feed starfish is actually quite simple. Put the food near them. If need be, place the starfish directly over the food to make sure it gets the food rather than other critters in the aquarium.
They are typically nocturnal, but they will adapt to daytime feedings if you need them that way.
The most important thing is to research your specific species’ diet before you introduce them to your aquarium. Some species may eat your stocked corals or other critters.
Let’s take a deeper look into what do pet starfish eat by looking at specific species starfish food.
Species Specific Diets
Because the differences vary so widely between species, here’s a list for folks to see which ones eat what.
Chocolate Chip Starfish
Chocolate chip starfish dine on shrimp, squid, chopped clams, sponges, soft corals, and tubeworms.
Crown of Thorn Starfish
Crown of thorn starfish eat the polyps of hard, relatively fast-growing stony corals like staghorn corals.
Marble Sea Star
Marble sea stars do best with live rock from which they can forage for detritus and mico-organisms. Supplement their diet with shrimp and flaked foods, as well.
Sand-sifting starfish need direct feeding via the sand bed. Food like shrimp, mollusks, and urchins will feed them, but they will quickly clear out detritus and excess food. They need supplementation or they will starve.
This one doesn’t need a whole lot of supplemental diet when they’re introduced into a well-established aquarium. If they do need supplementation, they’ll need clam meat or tablets placed underneath them.
Pacific Blood Starfish
This popular species eats bacteria, sponges, and planktons.
The leather starfish eats sea cucumbers, sponges, anemones, chitons, hydroids, fish eggs, and sea urchins.
Sunflower sea stars eat sea cucumbers, sand dollars, clams, crustaceans, mussels, sea urchins, fish, and gastropods.
Egyptian Sea Star
This species of starfish eats sponges, algae, and snails.
How Do You Feed a Pet Starfish?
Starfish have their mouths on their underside. To make feeding easier for them, place the food directly under them. Some species – though rare – may even eat straight from your hand.
Do starfish eat snails?
Some species of seastar eat snails. One species of seastar eats snails is the Egyptian Sea Star.
Do starfish eat algae?
Some species of starfish eat algae. Egyptian Sea Stars eat algae, for example.
Will starfish eat your pet fish and corals?
Some species are perfectly safe to keep with your other pet aquatic friends, while others will go after some of the pets you keep. The crown of thorn starfish, for example, may eat your corals because those are its natural diet. Other species, like the chocolate chip starfish, may find your shrimp or sand dollars a tasty snack. Be sure to study carefully before introducing starfish into your established aquarium.
Do starfish eat fish?
Some species do eat fish or fish eggs, though most do not. Be sure to study your specific species to determine if your species will eat the fish you stock or not.
How often do starfish need to be fed?
Starfish typically need to be given food every two to three days. You can determine the frequency by placing food near the starfish. If the sea star eats the food immediately, the starfish is hungry. You should adjust your feeding schedule accordingly to avoid your starfish from getting too hungry.
Will my fish eat my sea stars?
Thanks to the bony, calcified skin that protects sea stars, most of them are safe from your pet fish. They also are able to camouflage themselves, despite their striking colors, to help ward off potential attackers.
Are there any freshwater sea stars?
Starfish are purely saltwater animals. There is not a single species that’s been discovered that lives naturally in freshwater.
Looking for more interesting facts about what aquatic creatures eat? Check out our post on what tadpoles eat here.