After the occurrence described in Item 14, the phytoplankton concentration . Even though the amount of sunlight continues to increase, the phytoplankton change occurs because of the abrupt reduction in the nutrient concentration. This reduction comes about as phytoplankton, through photosynthesis, combine nutrients with carbon dioxide and water to form organic compounds. The dramatic phytoplankton population growth depletes the nutrient concentration and leads to the inevitable reduction of phytoplankton.