Starfish are some of the most fascinating creatures out there and scientists are still discovering new things about their peculiar bodies, diets, and effects on the ocean floor biome. We do know quite a bit about them already too, including what they eat and how to care for them as pets. So, let’s go over what do starfish eat in the wild and in aquariums.
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In the wild, starfish live in the saltwater seas and oceans of the world. These awesome animals are invertebrates because they don’t really have backbones. They are also classified as echinoderms and are closely related to sea urchins, sea cucumbers, and sand dollars, and they can be found in almost any saltwater environment – from the waters of the warm tropics to the cold waters of the Arctic and Antarctic oceans.
This shouldn’t be much of a surprise given that there are about 2,000 species of sea stars in the world. Most have the body structure we tend to imagine when we hear about starfish – five limbs going out of a small body with suction cups and a mouth on the starfish’s lower side and spiny skin on the top. In fact, that’s what “echinoderms” means – that these creatures have hard calcified skin.
Many of the thousands of starfish species don’t just have five limbs, however. Some can even have as many as 40 such as the Labidiaster annulatus, also known as the Antarctic Sun starfish or the Wolftrap starfish, common to the Antarctic ocean.
Another commonality between starfish, regardless of where they live, is that they do not have fins, scales, or gills, like other fish. They don’t even have blood either. Instead, sea stars use saltwater as blood by pumping it through their bodies and carrying all the nutrients they’ve consumed via that saltwater thanks to the starfish’s special type of “water vascular system”.
Whether cold water or warm water, starfish can often be found on a reef, eating whatever they can find on the sea floor including the corals themselves. They also reproduce like most other fish – by females releasing eggs in the water and males fertilizing them by releasing sperm.
The number of these mass-fertilized eggs can often number as much as 2 million or more from a single female. The eggs then hatch into free-swimming starfish larvae that eventually settle on the sea bed after twenty or so days and morph into adult starfish.
How Do Starfish Eat?
Before we go into the varied diet of starfish, let’s go over the bizarre way in which they feed. At first glance, a starfish doesn’t look like it could even feed itself nor store a substantial amount of food in its body. However, a starfish has everything it needs – countless suction “tube feet” or cups on the lower part of each of its limbs that help the starfish move and feel out potential prey, “eyes” or light sensors on each limb as well, a mouth on the lower part of its torso, and a stomach too.
In fact, most starfish have two stomachs – a cardiac stomach and a pyloric stomach. So, most starfish feed by extending the cardiac stomach outside of their bodies through their mouths and using its digestive enzymes to start digesting the food before it has technically been “eaten”.
After that, the cardiac stomach would gather the semi-digested food and bring it inside the starfish’s body where it’d go into the pyloric stomach that’d then digest it further.
What Do Starfish Eat In The Ocean?
The preferred prey of most species of starfish include mussels, clams, oysters, and other mollusks. However, starfish are both primary and secondary consumers in their food chain. This means that as “primary consumers” they can directly consume the “energy producers” of the food chain, i.e. the organisms that live off sunlight and transform it into energy. And, as “secondary consumers”, starfish can also consume other primary consumers.
This means that they also feed on algae, multiple types of plankton, coral reefs, and various organic materials as well as other primary consumers such as barnacles, numerous species of sea snail, clams, hermit crabs, mussels, oysters, sea urchins, seaweed, and even other types of starfish and some slow-moving small species of fish they can catch.
In short, starfish are very opportunistic, highly adaptable, and flexible predators and scavengers. Obviously, there are significant differences between the thousands of species of starfish too, with some leaning more into scavenging and others – into predation. The exact diet each specie has also largely depends on its environment and what can be found in it.
What Do Starfish Eat In An Aquarium?
If you want to look after a pet starfish in a tank, there are quite a few things to note first as this isn’t a beginner-friendly pet. Most starfish will require a large tank of at least 100 gallons or more.
This is crucial as the bed of the tank needs to be wide enough and covered with plenty of rocks and surface area for the starfish to explore and feed off of. Many species of starfish will starve even if you throw enough food in the tank but there isn’t enough area to cover at the bottom.
Next, it’s important to do plenty of research on your particular specie of starfish before you buy it or start looking for its food. Also, note that fish stores are not infallible and often make mistakes with starfish names, species, and diets. This isn’t an ordinary pet and you can’t expect every pet store clerk to be without error.
This is important because some starfish species are enthusiastic carnivores that will gladly chew their way through the invertebrates in your reef tank regardless of how many fish pellets you throw at them as an alternative. Other starfish species, on the other hand, aren’t as aggressive.
In essence, before you get to what do starfish eat, you’ll need to replicate your pet’s exact natural environment if you don’t want to either starve or eat things it isn’t supposed to. Depending on the species, its preferred environment may be coral reefs, seagrass, tidal pools, a rocky shoreline, or mostly just seabed sand.
Once you’ve got the bottom of the tank sorted, it’s time to start putting edible things on it. Most starfish species are essentially grazers so they will eat almost anything they find on the floor, be it pellets, kale, vegetables, fish flakes, spinach, or other organic materials.
Many species such as the Serpent’s starfish will even scoop up the detritus that has built up on the water bed. In doing so, your starfish will essentially clean its own tank.
What your pet sea star will usually prefer to eat the most, however, are mollusks. So, if you want to keep your starfish healthy and happy, a big portion of its diet should include live mussels and clams placed on the tank’s water bed. You can buy those from most supermarkets, just make sure to rinse them properly before putting them in your starfish’s tank.
For a few extra options and diversity, you can also give your starfish some frozen prawns, shrimps, and sponges, although the latter should not be frozen, ideally.
Different Starfish Species And Their Diet
We can’t go over all the thousands of different kinds of starfish in a single article so you will need to do some extra research on the particular species you’ve chosen as a pet.
Some of the more common species of starfish include the Chocolate Chip Starfish, the Blood Star, the Crown of Thorns Starfish, the Egyptian Sea Star, the Marble Sea Starfish, the Sunflower Star, the Sand Sifting Starfish, the Linckia Starfish, the Pacific Blood Starfish, the Leather Starfish, and others. So, let’s quickly go over some of those to give you some idea of what to feed them:
- Marble Sea starfish need lots of live rock as they feed by foraging the micro-organisms and detritus off the rocks. You should add some extra flaked food and shrimp pieces to supplement that diet.
- Chocolate chips starfish are predators and rely on an abundance of shrimps, chopped clams, and even squid. They will also readily consume tubeworms, sponges, and soft corals so you can keep them in a tank with corals.
- Linckia starfish are very easy to look after as long as you put them in a well-established aquarium that’s been full for about a year or more. That’s because they mostly feed on sponges and bacteria film. Once that is present, you’ll only need to occasionally supplement your starfish diet with some small clams or fish food tablets.
- Sand sifting starfish is very quick to clear out the detritus and food left-overs present in an aquarium so it needs lots of food supplementation. This means plenty of sea urchins, mollusks, and shrimps.
How Often Should You Feed Your Starfish?
This can vary greatly depending on the exact species, age, and environment of the starfish. Most specimens will need to be fed once every two or three days. You should be able to pick up on your pet’s individual preferences after a while, however, by just observing how often and when it ignores the food you drop in the tank, and when it goes after it enthusiastically.
As for a particular time of day – most starfish are typically nocturnal and will prefer to feed in the evening or after midnight. However, when they live in aquariums they can easily adapt to a daytime feeding schedule after a while.
The exact time and manner of feeding is also important if you have other fish in the aquarium. It’s not uncommon for other species to go after the starfish’s food if they are hungry too. This can be a problem as most pet fish species are much quicker than a sea star.
You can go around this issue with a couple of simple tricks:
- Feed your other fish before you feed your starfish – this way they won’t be as hungry and eager to steal their roommate’s dinner.
- Once you drop your starfish’s frozen shrimp or clam on the tank’s floor you can just pick up the starfish and place it on top of its dinner.
Ideally, you won’t need to do the second point as your starfish will enjoy exploring and looking for its own food. It’s ok to do it at the beginning or every once in a while, however.
What Are The Starfish’s Predators?
While lots of starfish can eat crabs and shrimp, the opposite is also true. There are many species of shrimp, snails, and hermit crabs that thrive on starfish prey. For example, the giant triton marine snail is common in coral reefs across the Indo-Pacific region. These snails are very fond of the common Crown of Thorns starfish.
This is actually a great thing from the reefs’ point of view as thorns starfish are a huge menace for quickly-disappearing reefs such as the Great Barrier Reef near Australia. This issue is largely man-made as we hunt a lot of the other natural predators of starfish which makes these multi-limbed invertebrates overly common in many areas of the ocean.
This isn’t just curious trivia either, however. There are some common fish pets that also fall on the list of common starfish predators. Some of them include pufferfish, triggerfish, parrotfish, boxfish, and others. Having a starfish in a tank with any of these fish will be a problem for the multi-legged invertebrate.
All in all, starfish are a great pet that can be quite fun to look after. Once you get the hang of what do starfish eat and what environment they need, caring for them is pretty easy too. The first few weeks are crucial, however, as is the research and preparation you’ll need to do beforehand. That period Is why starfish are generally seen as a pet that’s not beginner-friendly. That and the fact that most of them thrive in well-established aquariums that have been running for a while.