Flower is right...your lionfish did not do this...seriously. They won't even LOOK at sea stars...in fact, snails and hermits are also safe from lionfish.
You have sandsifting stars there, and unless you have a very large, well-established sandbed, they will starve (they also deplete your sandbed of beneficial fauna as this is what they eat). Stars are also very sensitive to water quality, particularly nitrates, and will deteriorate due to bad water quality, copper treatments, etc.
If it's not lack of food or water quality, I'd be looking for a hidden hitchhiker that is doing this.
How long have you had the stars?