Coral live in tropical oceans where nutrients are very scarce. Coral are colonies of tiny animals which trap plankton for food. There is very little plankton in tropical ocean water. However, within the tissues of the coral live symbiotic algae which photosynthesize using nutrients liberated from the animals ingested by the coral, passing some of the organic matter produced back to the coral. This tight nutrient cycling enables the coral reef to be one of the most productive ecosystems in the world, even though the surrounding ocean is no more productive than a terrestrial desert.
Most higher plants have mycorrhizal fungi associated with their roots.
The minute filaments of the fungus greatly extends the surface area for absorption of nutrients. The fungus also breaks down organic matter, liberating nutrients which are passed directly to the plant roots. The plant, in turn, passes carbohydrates to the fungus. Many plants will only grow with mycorrhizae on their roots. Nearly all herbivores have special fermentation chambers in their gut where micro-organisms break down some of the more resistant plant materials.