I've got same on the sand where the nerites won't go, though I don't know if they will or won't eat it. Mysteries aren't interested.
Interestingly it's only in the area away from the structure (plants & bamboo) suggesting somebody over there is eating it. An RTS in the bamboo, one or two juv.shrimp (Macrobrachium?) underneath & an occasional sneaky-sneaky amphipod is persisting, it seems, as I see them in the filter.
An excuse to get a few fan shrimp (AKA vampire shrimp) at the river next week, see if they dig it.