Since plants are the only organisms able to produce new food from inorganic matter, the rate of photosynthesis determines the production of organic carbon compounds and, ultimately, the availability of food in the Bay ecosystem. To illustrate how these factors affect the productivity of the Bay, let's look at the Chesapeake's most abundant food producer-the phytoplankton. Like all plants, phytoplankton require sunlight, nutrients and water. In the Bay, water is never a limiting factor. However, the amount of sunlight and nutrients can limit phytoplankton growth.
Temperature also controls the rate of photosynthesis.
Nutrients in the form of carbon dioxide and usable nitrogen and phosphorus are rarely available in the exact proportions required by plants. Normally, one nutrient is in short supply compared to the others and is considered the limiting nutrient. If a limiting nutrient is added, a growth spurt may occur. Conversely, reducing the amount of a limiting nutrient causes plant production to decline. Phosphorus controls the growth of some phytoplankton species in the spring, especially in the tidal freshwater and brackish areas.