I've only had trouble with amphipods devouring my Ulva, so I try to keep a good supply of it growing to keep them away from the pretty stuff. The snails only seem to be interested in decaying plant material, so I seldom see them on the good stuff. They will typically clean up the decaying part and leave the healthy growth alone. It could be your hitchhiker macros were starting to fade, thus triggering the CUC into action.
Also depends on what your CuC consists of. Small nerites and dwarf ceriths will only take care of the above mentioned decay and dying parts, with the exception of Ulva I've found. If you have Turbo Snails, emerald crabs, or urchins then they will demolish soft macros.
Edited by NinjaBum, 10 September 2011 - 07:17 AM.