Just like food webs in terrestrial, or land, environments, marine food webs also describe the interactions between organisms that feed on one another in a set environment. A marine food web can involve many different creatures in a complicated set of connections, but our picture shows a simplified web to help you clearly understand the different types of life in the oceans and how they are connected.
Photosynthesis is the basis of most marine food webs, just like on land. In shallow water, light can penetrate down to the sea floor where plants can grow underwater using photosynthesis to produce their own food. In deeper water, phytoplankton (floating algae, diatoms, dinoflagellates, cyanobacteria, and plants), float at the surface level and also produce their own food using photosynthesis. Together, these two groups are called producers.
Zooplankton, which are small animals that float on the ocean waters, eat phytoplankton. Many benthic, or bottom dwelling, organisms feed on plants or filter plankton out of the water. These animals include sponges, sea stars, anemones, crustaceans, clams, and more and are considered primary consumers.
Secondary consumers are creatures that prey on primary consumers and include fish, whales, and some sharks (also fish!). These animals eat things like crustaceans, zooplankton, and clams. Even though the blue whale is the largest animal living on the earth, it eats only zooplankton which it filters out of the water.
Tertiary consumers include animals that eat secondary consumers, such as predatory fish. Some sea birds catch and eat fish and are considered tertiary consumers in the marine ecosystem. At a level above them, sharks, whales, and other marine animals which feed on other predatory animals can be considered quaternary consumers.
All of these marine creatures are connected to each other in a delicately balanced marine food web!