My black serpents stars' arm fell off!!

[kookerson]

Im not sure if it was ripped off or if it fell off, but assuming it wasnt a predator, what else could cause this? Im pretty sure that there arent any predators in the tank (A goby, a firefish, a coral beauty angel and a scooter blenny), so is there any other reason that this would happen?

 

[woodycb]

My serpant star has lost an arm before, not sure how it happened but they grow back.

 

[KUDA]

Stress from acclimation or a rapid change in the water quality or salinity could cause a starfish to drop arms.