Dolphins live in all oceans of the planet and even in some important rivers.
Most dolphins live in the ocean, but there are some species which live in rivers.
The different species of dolphins live in most of the different climates of the world
Dolphins are important to the environment because they are able to be good natural indicators of the environment health.
Dolphins are important to the ecosystem in the sense that they are apex or top-level predators which control populations of fishes and squids and keep the ecosystem balance.