Phytoplankton are the start of the food chain. They have no biological predators; they live off of the energy of photosynthesis and nutrients. They are the biggest source of oxygen; they determine life on Earth. They are also part of the process that creates fossil fuels. The nutrients which they need are nonorganic, organic and traces of metal. These are all elements found naturally. Depending on the ratio of these components, different types of phytoplankton will start reproducing which helps regulate the density of phytoplankton. Human activity uses and produces elements that can either harm or are nutrients to phytoplankton. On one hand, human activity contaminates the water causing the annihilation of the phytoplankton which means no more production of oxygen in the water. On the other hand, human waste can be a nutrient to phytoplankton. We can see that phytoplankton are mostly present on the coasts and more precisely where there are dense populations. These nutrients allow the phytoplankton to over reproduce which creates a dense layer at the surface of the water, blocking the light. As the phytoplankton dies, their bodies are decomposed by bacteria in the water which consumes all the oxygen and produces carbon dioxide. The excessive nutrients in the water can also lead to the over growth of a type of plankton that is toxic. Disturbing in either killing or over nourishing the phytoplankton, leads to an eutrophication of the water. These create Dead Zones. æHumans are damaging what is the source of life.