Marine Biologists study saltwater aquatic life. The world's seas and oceans contain saltwater ocean life. Some ethereal lakes contain saltwater. Marine Biologists also study aquatic habitations. These are the fundamental places and conditions, in which plants and animals live. Marine Biologists also probably might study ecology. Ecology is the study of the interaction between plants and animals in their natural habitats. Marine Biologists sometimes use their knowledge to help keep aquatic environments healthy. They do this in many ways; some marine biologists keep track of fish population for the government or fishing companies. This helps governments and fishing companies set fishing limits. Other Marine Biologists care for aquatic life at zoos or aquariums. These Marine Biologists decide which foods animals eat. They also make sure that plants and animals live in healthy environments. Marine Biologists may study fishes insides to figure out the fish's solitary diet.