I've been doing some snorkeling at Olowalu beach right at mile post 14 on the west side of Maui. The water is shallow, I mean scratch yourself against coral shallow, but there are lots of little fish nurseries and a large variety of creatures to find if you look around. The first time I went there were waves and I got a little nervous about getting trapped in the shallow coral. After getting scratched on my hand I decided to head for the sand and just watch the fish from the beach for a bit.
Coral is not something you ever want to touch. First - it is bad for the coral. Second - it is razor sharp. You'll be cut to ribbons before you even notice. Third - coral is made of a bunch of tiny living things, things you don't want in an open wound. By the time bits of broken coral make it to the shore they have been polished near smooth, but living coral? Don't touch!
I went out again to mile 14 on a calmer day and the snorkeling was much better. There were so many fish! Still, I was wary of getting too close to any coral and preferred to stay in the deeper waters on the edges of the coral rather than trying to float above the large tables of reef.