Every food web originates with a producer, a plant that converts sun energy into food energy. But these vast fields of Spartina in San Francisco Bay are not consumed by animals. This grass is only broken down by microbes. These microbes are then food for protozoa, invertebrate larvae, and birds such as herons and egrets. (Insets: Left-Cattle egret. Center-Great Blue Heron. Right-Great egret.)