Remember that 80 percent of all Earth’s life is found in oceans. You may not be able to see them from shore or even from a boat, but beneath the waves are diverse habitats that support huge communities of plants and animals.

On land are rainforests; in the ocean are coral reefs. The “forests” of the sea are populated by giant kelp, a type of algae. At first glimpse, a desert might seem dead, but it supports many species especially adapted to survive the dry, harsh conditions. Being dry isn’t an issue in the sea, but at the ocean bottom, the pressure is intense, the water temperature is near freezing, and there is no light. Still, animals thrive in this seemingly inhospitable place. Near the ocean’s boundaries are estuaries, tidal flats, and wetlands such as mangrove swamps that bridge the land-ocean barrier and serve as veritable “nurseries” for many species of fish, shellfish, waterfowl, and crustaceans.

On land, the primary producers in the food chain are plants, and the same is true in the ocean. However, the plants in the ocean are microscopic phytoplankton. Phytoplankton and tiny ocean animals called zooplankton are abundant enough to feed an entire ocean. The Earth’s largest sea creatures-baleen whales-feed on plankton and krill, tiny shrimp-like creatures. As in any food chain, there are producers and consumers, including predators. A simple ocean food chain might look like this: Zooplankton eat phytoplankton; small fish eat zooplankton; jellyfish eat the small fish; and, finally, sea turtles eat jellyfish.