Animals in the sea include seahorses, sharks, jellyfish, tuna, crabs, cuttlefish, octopus, turtles, oysters, whales, abalone, hairtail, minnows, red-winged fish, hooked fish, dolphins and sea lions. There are algae plants in the sea, such as cyanobacteria, red algae, brown algae, green algae, coral, kelp, sponge, spirulina, charophyte and so on.
Animals living in the sea are mostly aquatic animals that have never lived without water in the process of species evolution, or aquatic animals that have changed from terrestrial animals to aquatic animals. They can breathe aerobically in water. For example, whales breathe with their lungs.
The plants in the sea are mainly algae, and occasionally there are others, such as algae, which reproduce very fast. Therefore, the crazy growth of algae in some sea areas will cause seawater eutrophication, which will affect the life of marine animals and the growth of nearby plants.
These animals and plants are interdependent. For example, after animals die, rotting corpses become the nutrition of aquatic plants. Many plants are food for animals, so no one is needed.