Plankton needs sunlight, water, and carbon dioxide to survive. Phytoplankton, the primary food source in the ocean ecosystem, use chlorophyll to make their food. They are typically buoyant and float on water to access all these essentials. Zooplankton feeds on these plant-like materials. It’s important to add that plankton also needs a population-free environment to survive. Without this, their life remains at risk even if they can make food well.