Have you ever wondered what that itsy bitsy starfish is doing in your tank? The sneaky starfish probably hitchhiked its way in on some live rock or new coral, but now there are dozens of small grayish starfish roaming your tank. It’s likely that this ‘outbreak’ of echinoderms is in fact the Asterina starfish.
The Asterina starfish is seen as more of an aquarium pest than a pet, and although most species of Asterina can coexist in your tank without killing your corals, it can be difficult to tell which species of Asterina you’ve inherited. It’s true that some Asterinas can grow up to be coral munchers, but by and large Asterina are innocuous members of a mature reef aquarium population.
If you are keeping a reef tank, we can almost assure you at one point you will come across an Asterina starfish. It is up to you what to do with them as a consensus has still yet to be reached whether the Asterina is friend of foe. Should a starfish outbreak occur you want to keep monitoring your corals, especially the base of the coral. If you start noticing jagged white marks it’s possible your starfish have gotten a taste for corals polyps and it is best to remove them from your aquarium.
Asterina stars reproduce by fragmentation (fissiparous reproduction) and their bodies will split apart losing one or two legs at a time which regrow as new starfish. The Asterina star can have an asymmetrical appearance, and it could look like your have a bunch of 3 legged starfish crawling around in your tank. This is also why it can seem like suddenly overnight what used to be a handful of tiny starfish are now covering your rock work.
Asterina starfish are small, around 1/4” – 1/2” across and can reach a maximum size of 3/4″, or 2cm. As you can image it would be difficult to remove each starfish one by one. If you’re ready to rid your reef of Asterinas it’s time to enlist the help of the Harlequin shrimp. This beautiful crustacean is a starfish killing machine and will seek and destroy your starfish by rolling them onto their backs and devouring their delicious tube feet. They will rapidly consume an infestation of Asterina after a few weeks or months of adding Harlequins.
If you do purchase a Harlequin clean up crew make sure you continue feeding them starfish or sadly they will die. You could also join forces with a few reefing friends and share the shrimp amongst a few hobbies to keep your Asterina populations in check.