The title to the beds of all nonnavigable tidewaters where the tide regularly ebbs and flows shall vest in the owner of the adjacent land for all purposes, including, among others, the exclusive right to the oysters, clams, and other shellfish therein or thereon. If the water is the dividing line between two parcels of land, each owner's boundary shall extend to the main thread or channel of the water. If the main thread or channel of the water changes gradually, the boundary line shall follow the same according to the change. If for any cause the water takes a new channel, the original line, if identifiable, remains the boundary. Gradual accretions of land on either side accrue to the owner of that side.