A scientist is studying an aquarium ecosystem that contains water, plants, and fish that eat those plants. The aquarium has glass walls so light can get in, but it is sealed so no material can move into or out of the tank. When the scientist turned the aquarium's light on, carbon in the water started decreasing. How is carbon moving and what is happening to the amount of carbon in the living things inside the aquarium? Explain your thinking as completely as possible. (Written response)