days and reproduces asexually. The reproduction phase creates 1 or 2 zoospores which grow inside of the parent's cell wall until they become new cells. Observed in the laboratory under culture, asexual reproduction begins when the protoplast contracts away from the parental cell wall. In P. fusiformis, the protoplasm contracts near the middle of the cell forming two lobes, as opposed to Pyrocystis lunula, which forms crescent moon-like shapes while dividing. Once the protoplasm divides, it differentiates into reproductive cells. These cells then swell very quickly, creating new parent cells. Ecology Phytoplankton including P. fusiformis play a large role in global carbon cycling by fixing carbon while also producing a large amount of oxygen through photosynthesis. Some oxygen produced by phytoplankton is dissolved into marine waters and helps support respiration for heterotrophic organisms. However, large quantities of oxygen diffuse into the atmosphere through surface waters, contributing up to 50% of the world’s atmospheric oxygen. Phytoplankton also form the basis of the marine food chain and are preyed upon by various organisms, such as grass shrimp, mosquito fish, mysids, and copepods. They contribute to the primary production of the ocean through the fixing of carbon into usable energy. It is estimated that P. fusiformis occurs most frequently at a depth of 60 and 100 meters in marine waters, tropical and subtropical bays and also oligotrophic waters, and has been found as deep as 200 meters. This species has been found in Taiwan, the Adriatic Sea, Black Sea, Canary Islands, Baja California, Brazil, India, China and Australia. In oligotrophic water, nitrogen (N) is a limiting nutrient for phytoplankton growth. Nitrate (NO−3) and ammonium (NH+4), both inorganic form of nitrogen, are most often taken up by phytoplankton and are necessary for growth and metabolic processes. P. fusiformis is known to metabolize both nitrate and ammonium at relatively equal rates during both the day and the night, and is able to take in nitrate at depths of 120m or greater, deeper than many other phytoplankton. P. fusiformis is also able to take advantage of surplus carbon (C) in surface waters by using what it needs for metabolic processes immediately, and then catabolizing and storing excess C for use at greater depths, allowing it have a relatively constant rate of cell division throughout the euphotic zone. Human interest P. fusiformis is interesting to humans as a natural phenomenon to observe in the ocean, in addition