Algae are producers. This means they produce their own energy, usually through photosynthesis. Like most producers, algae turn sunlight, carbon dioxide and water into glucose for energy.
Algae are fundamental to the marine food web, because consumers depend upon these photosynthetic organisms for energy in some way. For example, primary consumers, such as certain crustaceans, are herbivores that feed directly on algae to obtain energy. Herring are an example of secondary consumers, which are carnivores that get energy by eating primary consumers. Larger carnivores, such as salmon, eat herring. However, all consumers have benefited from the energy provided by algae. Algae come in many forms, from single-cell organisms to kelps that reach 65 meters long.