But soon, the scene changes. Using special paddles that have become my virtual “hands,’’ I “touch’’ a stream of bubbles shooting up from volcanic vents on the ocean floor that are releasing carbon dioxide. Over time, carbon dioxide entering the oceans from these vents, as well as from the atmosphere, will react with water to produce carbonic acid, a noxious substance that leaves corrosion — including destroying the shells of crustaceans — wherever it goes. I look around. The reef is no longer so colorful. Brown fuzzy algae has taken over the rocks, and things look murky. Many animal species have disappeared. I can’t see any sea snails at all.