Some will eat phyto, cyclo, and other small foods. but if the coral is photosynthetic, you don't really need to feed it.
What types of clams are you talking about? Tridacnid clams, like croceas, maximas, and squmosas, only need to be fed when small, like under 2 - 2.5 inches. They also contain symbiotic photosynthetic algae and will be fine under strong lighting.
Steer clear of things like flame scallops, as they are difficult to keep alive in aquariums.