Environmental Protection Agency Narragansett Bay Commission University of Rhode Island Office of Marine Programs

Estuarine Science

Planktonic Community

1. What is plankton?
2. How do we investigate plankton?
3. Why are plankton important to the biological community of estuaries?
4. What types of plankton live in Narragansett Bay?


3. Why are plankton important to the biological community of estuaries?

Phytoplankton are sometimes called the grasses of the sea. Like land plants, they produce lots of oxygen through photosynthesis. During photosynthesis they use the sun's energy to combine carbon dioxide and water into simple foods. This process removes carbon dioxide from seawater and allows the water to absorb a lot of carbon dioxide produced in the atmosphere. This "global carbon cycle" helps regulate the temperature of our planet.

Plankton are an important source of food for larger animals. Phytoplankton are the first link in the food chain. They are known as primary producers because they produce the first forms of food. Zooplankton and other small animals that graze on the phytoplankton are known as primary consumers. These, in turn, become food for larger organisms such as bivalves, crustaceans and fish. The fish and other animals then become food for animals near the top of the food chain, such as harbor seals and man.

Thalassiosira nordenskioeldii
©Jan Rines
Thalassionema nitzschioides
©Jan Rines
Copepod nauplius
(Click for larger images)

Estuarine fish and shellfish depend upon phytoplankton for survival. Zooplankton are the intermediate link that transfers energy captured by phytoplankton to these animals. Since the phytoplankton are the primary link, they must be produced in great quantities to support the estuarine food web. If the plankton disappear, the chain is broken and the animals will suffer. On the other hand, some phytoplankton produce chemicals that are harmful to humans and marine life. These species are not abundant but in some cases are cause for concern in coastal regions.


1. What is plankton?
2. How do we investigate plankton?
3. Why are plankton important to the biological community of estuaries?
4. What types of plankton live in Narragansett Bay?


(Image credits are listed in Image Index)

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