Do Starfish Eat Corals?

This is a question that comes up a lot in reef aquarium forums, club meetings, and newbie hobbyists standing in a reef aquarium store. The short answer depends entirely on the species of starfish. The longer one goes into understanding starfish properly. For example, one wrong decision can quietly destroy a reef system. Let’s walk you through everything you need to know!

Are all starfish the Same?

The word starfish covers thousands of species found across our oceans, which means their diets are very different. Some starfish are scavengers, munching on detritus and uneaten food, while some are grazers, moving slowly across the sand and rock formations. And some starfish are destructive and active predators of coral tissue. 

The key mistake reef hobbyists make is assuming that because starfish move slowly, they must be harmless, but in reality, starfish are incredibly effective hunters. Starfish use chemical sensing to locate prey, and some species can evert their entire stomach outside their bodies to digest tissue externally. This means that they don’t need to bite as we do. The starfish simply position themselves above a coral and begin digesting it from the outside in - quite gross to watch, but super cool!

Starfish that are NOT Reef Safe

Crown-of-Thorns Starfish - Acanthaster planci

These starfish are the most ecologically significant coral predator among all starfish. In the Indo-Pacific, including the Great Barrier Reef in Australia, population outbreaks of crown-of-thorns starfish (CoTS)  have caused mass coral mortality in the past. For example, in Moorea, coral cover decreased from 40% to 5% between 2005 and 2010 due to a CoTS outbreak. 

One single CoTS can consume several square meters of coral per year. They also target hard corals, particularly Acropora corals - the exact species many of us hobbyists work so hard to keep and frag. CoTS are not found in the hobby, and you likely will never see one in a fish store, but understanding their impact gives important context to the broader conversation of starfish captivity compatibility.   

Sand Sifting Starfish - Astropecten polyacanthus

These starfish are frequently sold as cleanup crew additions. Sand sifters are coral-safe, but they come with a different red flag. They are extremely good at consuming the microfauna in sand - they are practically surface hoovers. This means that any amphipods, worms, copepods, or other small organisms found in the sand, which form the base of a healthy reef food web, will be sucked up. 

In mature, larger reef tanks, sand sifting starfish can coexist, but in most home reef tanks, they are not suitable because they constantly exhaust the sandbed’s biology, eventually starving your system. 

Chocolate Chip Starfish - Protoreaster nodosus

It is important to mention these guys as they are widely available in fish shops, are visually striking, and are sold without warning. Chocolate chip starfish are voracious predators. They will happily eat clams, sponges, corals, and other invertebrates, and they are absolutely not reef-safe. If you have a chocolate chip starfish in a reef tank, your corals will be at risk as they move slowly and feed at night, causing damage that is well underway before you notice something is wrong. 

If you urgently want one, they belong in a FOWLR  (fish only with live rock) aquarium setup if kept at all. 

Starfish that are Considered REEF SAFE

Brittle and Serpent Stars

These are technically not true starfish, but they are often grouped in hobbyist conversations. Many serpent stars are fantastic scavengers and are genuinely reef-safe. They come out at night and consume uneaten food and detritus, making great clean-up crew members. 

The green brittle star is one exception from the bunch. These have been observed actively hunting and consuming small fish and shrimp, so avoid these if you have fish and shrimp in your tank. 

Fromia and Linckia Species

These are the most popular starfish for reef tanks, and with good reason. Fromia stars are largely reef-safe. They graze on surface film and microorganisms found on the tank glass and rockword. 

Linckia star, specifically blue Linckia, are low-risk for corals. However, they do have a reputation for being challenging to keep long-term, as they require very stable parameters and a mature, well-established reef system to thrive. 

Warning signs to look for

If you’re worried a starfish may be targeting your corals, look out for the following signs:

• Localised tissue recession - particularly at the base or underside of the coral

• A starfish that is constantly positioned on or very near the same coral for a few days

Remember, trust your instinct. If something doesn’t look right, investigate. The problem with coral predation is that hobbyists often jump to conclusions and point the finger at water chemistry issues. While this may be the case, the culprit could actually be slowly walking across the rockword when the lights are out.

Check your water parameters to see if they are stable. If they are stable but you’re still seeing unexplained tissue loss, it’s worth being on night-watch to see what is moving around your system. If your starfish is disrupting your tank, remove it to an isolation chamber asap. 

Questions to ask yourself before buying starfish

Over the last decade, the reef hobby has boomed, and the availability of marine life from online suppliers and local stores means there is a lot to choose from. However, this can lead to uninformed purchases. 

Before adding any starfish to your reef tank, ask yourself these three questions:

1. What does this species eat in the wild?

2. Has this starfish been observed predating coral or invertebrates in captivity?

3. Is my system mature enough to support starfish long-term?

If the person selling the starfish can’t tell you if a starfish is reef-safe or not, that’s useful information in itself. Quick tip - experienced fish and coral stores will know the answer. 

Summary

Starfish are one of the ocean’s most interesting and ecologically important animals. In the wild, they play key roles in maintaining the balance of reef ecosystems and controlling prey populations, but in our tanks, we need to learn from the devastating events like the crown-of-thorns, as that context matters. If you’ve got your eyes set on keeping starfish, you don’t have to avoid them entirely. 

Keeping starfish can be one of the most rewarding achievements if you select the right species, in the right reef system, and properly care for them. So, do starfish eat corals? Some do, very destructively and deliberately. But some starfish make perfectly peaceful neighbors. Knowing the difference between these two traits is the knowledge you need, and it is why this community here at Reefco Aquarium exists. At Reefco Aquariums, our team of experts is here to share what we’ve learned, so fewer stunning corals have to pay the price of uninformed decisions. 

If you are still unsure if a starfish is right for your reef aquarium, contact the Reefco Aquariums team today.