Keepers of the ReefSharon Wismer reef ecologist and mom is the best tour guide a kid could have for a visit to the underwater world of Australia's Great Barrier Reef. Alice Wong's richly detailed, accurate watercolors take a boy and girl snorkeling to see the fishes that maintain the ecological balance between the corals and their main competitor, algae. Without the fish species that brush, crop, scrape, excavate, and browse the algae, coral reefs would die. A coral