Aquarium Friend or Foe?: Micro Brittle Starfish

Spotted a tiny, starfish-like creature seeming to “walk” across your tank using a multitude of long, spindly and seemingly hairy arms? Or maybe you’ve noticed said spindly arms sticking out of your live rock? Fear not. It’s not an alien, just a micro brittle starfish!

Micro brittle stars can hitchhike their way into your aquarium on live rock or other material. Is that a good thing? Are these aquarium friends, or should you remove them from your tank? Let’s find out!

What is a micro brittle starfish?

There isn’t a single species of micro brittle starfish: this is a broad term applied to pretty much all brittle starfish that stay under 1″ in diameter. Brittle stars, by the way, are echinoderms belonging to the class Ophiuroidea, which has been around in our oceans for many millions of years.

As their name suggests, brittle stars are closely related to true starfish of the class Asteroidea. However, even non-aquarists will be able to spot the difference at a glance: brittle star legs are much longer and thinner than starfish legs, and covered in bristles. A good few species are kept in the aquarium, as they’re easier to care for than their starfish cousins, which are notoriously finicky and known for their low survival rates.

Larger brittle stars, like the popular Ophiocoma echinata, are creatures you’ll generally have to pay for at your local aquarium store. The micro varieties are a different story, as they’re common hitchhikers. They reproduce reasonably quickly and like hiding in live rock, meaning they often end up in your tank without any intervention on your end.

Identification

There are many species of micro brittle star, but not all of them tend to make their way into our aquariums. If you see one in your tank, it will usually (though not always!) be either of these two:

• Ophiactis savignyi (Six-Armed Brittle Star): With six* banded arms. This is probably the most common brittle star in the world, and it adapts very well to aquarium life.
• Amphipholis squamata (Dwarf Brittle Star): Whitish in color with five arms. It’s quite faint, but this species is actually bioluminescent!

*Arm mileage may vary, as starfish can lose appendages or accidentally sprout extra ones. There’s no difference between micro brittle star species in terms of care; they don’t really need much of anything from you.

Tip: If you spotted something small and starfish-like with more compact legs, it’s probably an Asterina instead. Brittle stars have long, stringy appendages.

Micro, or not?

We haven’t seen it happen all that often, but juveniles of larger brittle stars (or their very closely related serpent cousins, which lack the leg bristles but are otherwise almost identical) can sometimes hitch a ride into your aquarium as well.

If your brittle star keeps growing past 1″ in length, keep an eye on it to make sure you’re not dealing with the voracious giant green brittle star, Ophiarachna incrassata, which tends to develop a taste for fish in adulthood. Most other species, like the rather decorative banded serpent starfish, are unlikely to cause mayhem and can usually stay.

Micro brittle starfish: Aquarium friend or foe?

Micro brittle stars aren’t the prettiest creatures to be found in our tanks, that’s for sure. Often, the only visible parts are a few squirmy legs (between 3 and 6, usually) sticking out of rock crevices, giving a slightly creepy effect. But fear not: micro brittle stars mean well. In the vast majority of cases, they are aquarium friends.

Micro brittle stars have several useful characteristics:

• They don’t reproduce as quickly as Asterina stars, so they’re less likely to overrun your tank
• They’re scavengers that can make useful additions to your clean-up crew
• They’re totally reef-safe and won’t bother corals, inverts, or fish

Additionally, you usually don’t see micro brittle stars much unless you’re looking for them. Good news for those among us who don’t like their looks!

To remove, or not to remove?

There’s usually no need to attempt to remove micro brittle stars from your tank. They help deal with leftover food and other bits. In fact, they can themselves function as an additional source of nutrition for creatures nimble enough to pull them out of their hides, like wrasses, hawkfish, small puffers, and the wacky harlequin shrimp (the latter prefers true starfish, but will eat brittles as well).

In rare cases, brittle stars can start to overrun an aquarium—or at least parts of it, like sump or filter compartments. If this is happening to you, consider whether you may be overfeeding the tank. All those stars need food, after all, so a population explosion can indicate an excess.

Once you start cutting back on feeding (or start using less messy feeding methods, or cleaning the tank more often), the micro brittle star population should slowly start to stabilize. You can speed up the process by catching the stars using something like a DIY bottle trap left near the rockwork overnight with some bait inside.

Tip: If you’ve caught a bunch of micro brittle stars, check whether anyone wants them rather than culling them straight away. They may be useful to another aquarist, who may even be willing to pay for them—they make a great meal for starfish-eating creatures, such as harlequin and bongo shrimp.

Need help?

A thriving reef aquarium is one of the most beautiful pieces of home decor you can add to your space, but it’s also a lot of work to maintain and requires specialized knowledge of all sorts of creatures and natural processes—including hitchhikers like micro brittle stars.

Dreaming of a colorful tank for your home or business, but lack the time? That’s where the FantaSEA Team comes in! Contact us with your ideas so we can design, set up, and maintain your reef for you.

PS: If you like brittle stars and true starfish, don’t forget to have a look at our post on easy and reef-safe starfish for your aquarium.