I have heard that it is because the Hawaiian Islands are so young that the reef shelf is thin. Perhaps the topography has something to do with it also. The water temperature may account for the fact that there are only a few species of soft corals here. Nevertheless, the snorkeling and the scuba diving is exciting with a large assortment of reef fish and corals to be seen and no lack of large fish and mammals.
One of the best places to snorkel is Kealakekua Bay. There are three ways to get to that part of the Bay where the snorkeling is excellent: by boat, by kayak or by hiking several miles down, and back up, from the highway. There are several snorkeling trips to Kealakekua Bay offered.