Months back I noticed a cute mini starfish with misshaped arms. I did some research and identified them as Asterina starfish. I've read mixed reviews that they are harmless but I'm no so sure. Their population has exploded in my tank and when they attach to the zoanthids they close up. I haven't noticed them eating any but I'd rather not have them in there. Should I add a harlequin shrimp or some other natural predator or just let them be?