Ocean plants and animals come in a variety of shapes and sizes, from the tiny shrimp-like krill to the massive blue whale that feeds upon it. Across the vast expanse of the Pacific Ocean, a huge number of marine species thrive. The nutrient-rich waters support organisms in the Pacific Ocean on all levels of the food web.

When you think of Pacific Ocean plants, you probably imagine kelp forests and bright green seaweed drifting in the current. You might be surprised to find that kelp and seaweed are not true plants, but algae. Researchers classify true plants and algae into entirely different kingdoms!

One of the few types of true Pacific Ocean plants is seagrass. Seagrasses grow true roots, unlike algae, which attach to the seafloor via a ​holdfast​. Seagrass also produces seeds and flowers for reproduction.

Many different species of seagrass flourish throughout the Pacific Ocean and support entire ecosystems. Herbivores such as dugongs feed on the seagrass, while fish and invertebrates use seagrass as shelter from predators.

Though not true plants, kelp forests provide incredibly important habitats for a variety of organisms in the Pacific Ocean. The largest species of kelp can reach up to 150 feet long. Kelp forests provide shelter for fish and nurseries for the young of a variety of species. Predators like sharks and marine mammals cruise through the kelp to hunt for prey.

Pacific Ocean animals and plants rely on one another in marine ecosystems in many ways. Pacific Ocean plants provide homes to small animals of all kinds, and predators rely on the ecosystems built around these plants to provide prey for them to eat.

Many different marine mammals live in the Pacific Ocean. The cetaceans, or whales and dolphins, make up the largest group. Some notable species include the blue whale, killer whale, humpback whale and bottlenose dolphin.

The Pacific Ocean is also home to several unique marine mammal groups as well. Dugongs feed on seagrasses in the western Pacific. Sea otters forage for clams and sea urchins in the eastern Pacific. A number of different pinnipeds also range throughout the Pacific Ocean, including California sea lions, elephant seals, fur seals and more.

Fish provide some of the greatest diversity of organisms in the Pacific Ocean. Numerous smaller fish species provide important food to larger fish, sharks and marine mammals. These include herring, grunion, mackerel, sardine and more. The large predatory fish that feed on the smaller species include swordfish, marlin, tuna and salmon. A wide variety of sharks and rays also make their home in the Pacific. Some examples include the infamous great white shark, and the gentlest of giants, the filter-feeding whale shark.

Pacific Ocean invertebrates make up an important part of the food web. Crustaceans such as krill, shrimp and crabs provide important food to animals from elephant seals to blue whales. Cephalopods like squid, octopus and cuttlefish also feed various marine mammals and large predatory fish. Additional types of invertebrates, such as sea urchins and clams, provide food for sea otters and other marine predators.

When you think of the ocean, you likely don't imagine reptiles. However, six different species of sea turtle live and migrate through Pacific Ocean waters: the flatback, green, Pacific ridley, hawksbill, loggerhead and leatherback. In addition to sea turtles, you can also find several species of sea snakes in the western Pacific Ocean. Finally, you have the uniquely adapted marine iguana, which braves the rough waters off the coast of the Galapagos Islands to graze on algae.