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?


4. What types of plankton live in Narragansett Bay?

Narragansett Bay is home to a variety of plankton. Their abundance changes with the seasons. Phytoplankton bloom in the spring when more than 50 million cells per liter of water can be found in the Bay. Zooplankton, such as copepods, grow as they graze on the abundant phytoplankton. More than 100 zooplankton can be found in one liter of seawater during the spring blooms. Narragansett Bay is home to several hundred different species of plankton.

There are differences between the upper and lower Bay. Many oceanic organisms are found in the lower Bay, but not in the upper Bay. The upper Bay has more estuarine and freshwater species and is more productive than the lower Bay. An abundance of nutrients in the Providence River fuels huge blooms of phytoplankton. Some blooms called "red tides" are associated with polluted waters.

Phytoplankton

The phytoplankton species of Narragansett Bay are mainly diatoms and flagellates. Diatoms are single-celled plants that live alone or in colonies. These cells often form chains that resemble beaded necklaces. The most common phytoplankton in Narragansett Bay is Skeletonema costatum. Other genera of diatoms that are found in the bay include Asterionella, Chaetoceros, Ditylum, Eucampia, Leptocylindrus, Psuedonitzchia, Thalasionema, and Thalassiosira.

Skeletonema costatum
©Jan Rines
Thalasionema nitzschioides
©Jan Rines
Chaetoceros debilis
©Jan Rines
(Click for larger images)

Dinoflagellates are tiny single-celled organisms with long slender appendages called flagella. Dinoflagellates that are commonly found in the bay include the genera Ceratium, Gymnodinium, and Peridinium.

Some plankton grow rapidly and form blooms so thick that they change the color of the water. Mesodinium rubrum is a ciliate, a single-celled organism that has short hair-like structures called cilia. It can form very dense patches that are red in color, but it is not known to be toxic to other organisms. A QuickTime movie of Mesodinium is available at Jan Rines' Plankton Theater.

Zooplankton

The zooplankton of Narragansett Bay consists of many types of copepods, gelatinous organisms, and larval forms of many animals. The most common species are the copepods Acartia tonsa (most common in summer) and Acartia hudsonica (most common in winter). Other genera of copepods include Centropages, Eurytemora, Oithona, Paracalanus, Psuedocalanus, and Temora.

Eurytemora copepod Comb Jelly
(Click for larger versions)

Comb jellies are gelatinous animals with rows of comb-like structures that appear iridescent when they reflect sunlight. They look like jellyfish and drift with the currents like jellyfish but are not considered true jellyfish. They do not have stinging cells and are in a group called ctenophores. Comb jellies are voracious predators that capture food (such as copepods) with their long tentacles. They can devour large populations of zooplankton in the Bay.

Many animals, such as fish, bivalves, gastropods and polychaetes, have planktonic larval stages. These are considered "temporary" plankton because once the animals grow large enough they settle down to the bottom or swim away on their own.


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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