Some major animals are sharks, fish, and whales. There are many individual species in each of the categories. Such as blue whales, salmon, and great white sharks. Many fish have adapted in special ways for self-defense. For example cuttlefish have different colored pigments and rapidly changing colors to escape predators.
Many sea animals find shelter among the seaweeds, in rocky crevices, or under the sand.
Matching the colors and even textures of the background also helps sea creatures remain undetected. A fish designed to blend into the coral. Hard shells are useful protection, at least from weak-jawed creatures. Many fish have special tactics for defending themselves from predators or attacking prey. Some produce venom to defend themselves and often advertise their danger with distinctive markings.