In a food web, a group of organisms lives in a community. The movement of energy through the food web occurs first among primary producers, which are organisms that make their own food. Primary producers may use the sun’s energy via photosynthesis, or in the absence of adequate sunlight, they may use chemosynthesis. Consumers, or herbivore animals, eat primary producers. Primary producers play a crucial and irreplaceable role for life on Earth.
Primary producers form the bases of food webs and entire ecosystems. They produce their own food either via photosynthesis or chemosynthesis, depending on the availability of sunlight. Primary producers provide food for primary consumers or herbivores, which in turn provide food for carnivores, consumers at secondary or tertiary trophic levels.
Primary producers form the basis of a food web or tropic levels. Whether it's green plants using photosynthesis or benthic bacterial mats, these organisms provide food for consumers. Primary consumers are herbivore animals that eat primary producers. Carnivorous secondary consumers eat primary consumers. Tertiary consumers eat the secondary consumers. Eventually, the top member of a food web will die, and its body will feed decomposers. These decomposers provide organic material, converted for use by the next cohort of primary consumers, and begin the cycle again. Energy passes through each trophic level. However, throughout each step of the food web, energy is lost either as heat, for life processes such as movement, or in feces and decaying remains.
Plants, algae and photosynthetic bacteria comprise primary producers that use the sun’s energy for photosynthesis. Both terrestrial and aquatic primary producers perform this activity. In the water column, phytoplankton living closer to the water’s surface access the sun’s energy. Other primary producers in aquatic environments include seaweeds, algae, green plants, and blue-green or purple bacteria. They photosynthesize carbohydrates needed for energy. Phytoplankton comprise the foundation of ocean ecosystems, as many creatures from zooplankton to jellies to whales rely on them for food.
Some primary producers, such as some species of bacteria, do not use the sun for energy nor for fixing carbon dioxide. This process, chemosynthesis, occurs in the absence of sunlight, such as deep in the ocean around hydrothermal vents or cold water methane seeps. These primary producers metabolize inorganic material such as nitrogen, sulfur or iron to make food from carbon dioxide. These types of producers are called chemoautotrophs, and they form the basis of food webs for octopi, crabs and other sea animals. Chemoautotrophs can also be found in other hydrogen sulfide-rich ecosystems such as salt marshes.
The quality of primary producers directly affects the success of secondary consumers, and as a result, the entire food chain. Because of the interconnected nature of food webs, it is crucial for primary producers to remain intact. Even some of the smallest primary producers, such as phytoplankton, possess far-reaching effects. Many aquatic food webs rely on phytoplankton as primary producers. The different biochemical makeup of phytoplankton affects their nutritional value for zooplankton that feed on them. Biodiversity of primary producers, whether aquatic or terrestrial, yields greater success for herbivores because the animals have more nutritious options available.
Primary producers also rely on the work of decomposers to survive. Decomposers fix nitrogen so that it is available for primary producers. Various organisms work the soil to decompose organic matter and enhance its nutrients so that plants can grow and provide the basis of a food web. While different organisms can take the place of those that grow scarce, maintaining and protecting primary producers yields sustainable ecosystems.
