Examines how marine scientist Brent Hughes, working in Elkhorn Slough on the California coast, learned that sea otters were helping seagrass remain healthy despite fertilizer runoff from nearby farms, thereby solving a modern science mystery and uncovering secrets of the ecosystem. Features dozens of color photographs and charts, sidebars, activities, and conservation tips. Teaching Books: https://www.teachingbooks.net/tb.cgi?tid=54016.