Dead snails

I have 16 gallon tank with couple corals, 2 Firefishes, 1 yellow clown goby, 2 wurdemannis. I HAD 4 turbo snails, 2 ceriths, 3 nassarius and 2 fighting counches. Corals and fish are doing great. I have algae problems, so i thought snails will have enough food.



But in the last couple of weeks, 3 turbos and 2 ceriths died. Why? Wurdemannis ate all of them but i dont think they killed them?