An example of a decomposer is a fungus, such as a mold or mushroom. Decomposers are essential to ecosystems because they break down dead organic matter, recycling nutrients back into the soil. This process enhances soil fertility and enables the growth of new plants. Decomposers can also include certain bacteria and detritivores like earthworms. Their role in decomposition is crucial for maintaining ecosystem health and ensuring the continuity of nutrient cycles.