Everyone knows what a starfish is, but very few understand their structure and how they function. These are very unique and interesting aquatic creatures!
This is especially true for anyone who is planning on keeping one in their home aquarium. For many potential starfish owners, the process of feeding them can seem quite daunting (or confusing).
This guide will go over what starfish eat, how their diet varies based on location and species, and how they actually consume their food.
How Do Starfish Eat?
Right off the bat, the actual act of a starfish eating can seem quite strange. These iconic creatures hardly seem to move, and don’t appear to display any sort of “normal” eating behavior.
So how do they do it?
To understand this, we need to dive into their anatomy. Specifically, we need to understand their feet, arms, and stomachs (yes, they have two stomachs).
On the bottom of each of their arms, a starfish has thousands of little feet. These look like short tubes and are how these creatures slowly move themselves across various surfaces in the water.
But there’s more. A starfish also has an eye under the tip of each of their arms. This helps them navigate as well as look for food to eat.
Now let’s look at their stomach situation. Starfish don’t simply use their stomachs for digestion, they actually use it to “grab” the food they want to eat.
Here’s how the process works:
First, a starfish will move until it’s on top of what it wants to eat. As you can imagine, this isn’t a fast process (and their vision isn’t stellar). That’s why these sea creatures are essentially on the lookout for food at all times.
Once the starfish is in position, things get quite interesting. Through a process called eversion, the sea star will actually push one of its stomachs (the cardiac stomach) out of its mouth and envelop the food it’s going to eat. They are quite deft with this action, and can even slide their cardiac stomach into tiny mollusk shells. This process allows the starfish to begin digesting and absorbing their food with stomach acid.
After this process is complete, they’ll “retract” their cardiac stomach and hand off the rest of the digestion process to the pyloric stomach (aka stomach number two).
The Advantage Of This Process
You might be wondering why starfish would eat this way. It seems like there’s a lot of unnecessary steps right?
But as always, nature has a reason.
By bringing its stomach outside of its body to break down and digest food, a starfish is able to eat foods that would normally be too big for them. Instead of needing extra room to swallow a massive snail, oyster, or clam, they can essentially “liquify” the important bits for easy digestion.
That makes these animals one of the most efficient eaters in the world!
What Do Starfish Eat In The Ocean?
Starfish have a varied diet in the wild. This is influenced by their location and what foods or prey are nearby.
From a broad view, you’ll often see starfish happily eat mussels, oysters, clams, and snails. These are the perfect prey because they can be easily digested using the method described in the section above, and are easy to catch. But with that being said, some will even eat fish (if they’re able to get their arms around one).
In other situations, certain starfish will eat sea urchin, barnacles, bristle worms, coral polyps, and crabs. There’s a lot of variety in their diet, and it all depends on where the starfish lives and what food is available to them.
Author Note: Crabs are usually only on the menu for larger starfish. On the other hand, coral polyps make up a significant part of the diet for starfish (like the crown of thorns) that live in large reef systems. Some starfish will even eat other starfish! Like any food ecosystem, availability plays a big role.
Because starfish are constantly moving around in search of food, they’ll also do a bit of scavenging. This is especially true for starfish that aren’t very large. Foods like algae, seaweed, and decomposing animals or plants will get taken care of in short order (which makes them useful for certain home aquariums).
What Do Starfish Eat In Aquariums?
Providing the right food for your starfish requires you to understand the species you have and their natural environment. This typically means you’ll need to offer some variety if you want these creatures to thrive (you can’t go to the store and simply buy “starfish food”).
With that being said, they will usually consume some foods that will occur naturally in your tank. For more home aquariums, this typically means algae that has built up on various surfaces as well as fish food that has been missed by the other inhabitants of the tank.
But you can’t rely on that alone. Depending on what species of starfish you have, you’ll likely need to give them some mollusks to eat. Mussels, clams, oysters, snails, and even scallops are great food options. If you have any bristle worms around, those can be included in their diet too!
Author Note: When purchasing these foods for your starfish, it’s important to make sure you’re purchasing them from a reputable source. Also, make sure to give them a good cleaning before dropping them in your tank! Not only can unwanted chemicals be a problem for your starfish when eating these foods, but other critters in the tank could suffer as well.
If you want to mix things up a bit, consider adding some leafy greens to their diet as well. Kale, spinach, and lettuce are all common options. Make sure to boil them before feeding these to your starfish.
How Often Should You Feed Them?
Now that you know what starfish eat in a home aquarium environment, it’s important to cover their ideal feeding schedule.
While this can vary slightly based on the species you own, a good rule of thumb is to feed your starfish once every two to four days. This window of time will account for their digestion timeline and other variables that could impact their level of hunger (like if there was more algae than normal for them to eat recently).
In order to figure out if your starfish is hungry and ready to eat, simply place some food next to them and monitor their reaction. If they make a clear move to investigate and consume the food then they’re probably hungry and ready to eat. If they don’t show interest, it’s probably not time.
Some aquarists like to feed their starfish at night, since these critters are nocturnal. However, others like to let them gradually adjust to being fed during the day.
How Their Diet Varies By Species
In the sections above, we’ve covered what starfish eat in most situations. But with that being said, the species you’re dealing with will dictate what specific diet you’ll want to provide.
Here are the diets of some common species:
- Chocolate Chip Starfish: Sea urchins, snails, shellfish, shrimp, algae, and tubeworms. They will also eat coral (so be mindful of this)
- Brittle Starfish: Small invertebrates like shrimp, snails, and crabs.
- Asterina Starfish: Algae, coral, bristle worms, biofilm, and detritus.
- Marble Sea Starfish: Detritus, algae, shrimp bits, fish flake food.
- Sand Sifting Starfish: Small crustaceans, mollusks, bristle worms, feeder shrimp, and detritus.
- Panamic Starfish: Coral, shrimp, snails, algae, and sometimes other starfish.
- Linckia Starfish: Algae, detritus, biofilm, food flakes.
The Importance Of Knowing What Species You Have
Knowing what kind of starfish you have is incredibly important, and it’s easier to make a mistake here than you might realize. Some of the common species people keep as pets look very similar, and are mislabeled by their local pet store.
That means even though you might think you know what your starfish eats, you don’t. This could result in introducing a starfish into your tank that goes after your coral, or even the other inhabitants of the aquarium!
So take it from us, spend some extra time verifying the species you’re getting. It’s not worth the potential headaches if you get this wrong.
Do Starfish Eat Algae?
Starfish do eat algae, but their interest in it will vary based on the kind of species you’re dealing with.
For example, if you have an asterina starfish then algae will be consumed quite regularly (and will actually make up a reasonable part of their diet if it’s available to them).
On the other hand, a chocolate chip starfish will need other sources of food in order to survive. While it will probably eat algae it comes across, it’s not going to be the primary focus of its diet.
Do Starfish Eat Shrimp?
Certain starfish will eat shrimp if they can get ahold of them. Brittle, chocolate chip, and marble sea starfish are all examples of species that will happily snack on these crustaceans when they can.
That means if you have shrimp in your aquarium you’d like to keep around, steer clear of carnivorous starfish that are large enough to eat them. Despite their slow and unassuming nature, starfish are efficient predators!
Do Starfish Eat Coral?
This is another popular question when it comes to what starfish eat, and it’s understandable. Maintaining healthy coral in your tank can be challenging, and doing so can be a great source of pride for many aquarists.
And unfortunately, some starfish do eat coral. That means species like the asterina or panamic starfish are probably a bad choice. They’re obviously not doing it to be malicious, they’re just doing what you would do if you saw a tasty snack in front of you!
We hope this guide on what starfish eat (and how they do it) will make it easier for you to decide which species is right for you. Remember, spending some extra time to verify what kind of starfish you’re actually getting is essential. You don’t want to introduce one that wreaks havoc on your aquatic community!
If you have any questions about starfish diets or what foods they eat, send us a message. We’re more than happy to help you out!