Answer:
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 balance of the ecosystem.
Lately, the bottlenose dolphins have been identified as sentinels of the coastal marine ecosystems, because they consume of a wide variety of fishes and squids, they absorb pollutants in their bodies when there are high concentrations of contaminants in the water so scientists can have an idea of the status of the marine environment.