In Lessons 11 and 13, we learned that some of these non-living things are dissolved substances called salt and limestone. Tiny plants and animals that float in almost all bodies of water called plankton are some of the many living things existing in the ocean that are small and difficult to see. Despite their small size, plankton plays an extremely important role in supplying food not only to the coral reef system but the entire ocean ecosystem. Plankton that are plants are called algae, or phytoplankton . Plankton that are animals are called zooplankton .
Phytoplankton are producers .
This means that in the process called photosynthesis , they produce their own food using sunlight, water, carbon dioxide, and nutrients. As animals, zooplankton are consumers and as a result must capture their food. Look at the drawings above and notice that zooplankton have various food capturing devices in the physical appearance whereas phytoplankton do not. Using the process of photosynthesis, phytoplankton rely on the sunlight energy that passes through the surface of the water to live in the ocean. For this reason phytoplankton, or algae as its commonly called, lives within few meters of the surface of the water where there is plenty of sunlight.