At this point, I have seen no research that indicates that turbo's eat coralline. Their mouth is not designed to cut through the hard shell-like algae. War is correct that they will aide in the proppropagationthe coralline because they clean it as well as "brush" it when they move over it. This helps it release the spore into the water column.
Most of the time, the coralline dies off because of excessive lighting, fluctuation in water chemistry, or low levels of Ca
Urchins are known to eat coralline, but they provide the same service that a bear in the forest would. He eats the berries and then poops out the seeds a mile or so away. The long term effect is more coralline over the entire tank in a shorter amount of time than just natural growth.