Zooplankton and phytoplankton are commonly confused because they are both relatively small, live in aqueous environments and are the building blocks for marine life. The one key difference is that most zooplankton are animals and phytoplankton are plants.
Zooplankton have a wide variety of adaptations which allow them to float in their watery homes: flat or long bodies to increase their surface area, gas-filled floating appendages and oil droplet formation. They float closer to the surface at night.
Phytoplankton also adapt to their surroundings. Their shape is dependent on their environment.
Zooplankton eat phytoplankton and smaller species of zooplankton. In the spring, when the phytoplankton population increases, zooplankton will reproduce heavily to catch up with their food supply.
According to the NASA, phytoplankton need nutrients supplied by cool water currents to create their food through photosynthesis.
Scientist consider these tiny organisms to be a key health measurement of marine environments. Since zooplankton are a food supply for higher functioning organisms, like fish and whales, what affects zooplankton will also affect an entire ecosystem.
Phytoplankton also absorb carbon dioxide from the atmosphere. When they die, they sink. NASA says ocean depths are estimated to contain 90 percent of the world's carbon dioxide, much of it due to these tiny plants.