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

Estuarine Science

Benthic Community

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


1. What is a benthic community?

The Benthic Community is made up of organisms that live in and on the bottom of the ocean floor. These organisms are known as benthos. Benthos include worms, clams, crabs, lobsters, sponges, and other tiny organisms that live in the bottom sediments. Benthos are divided into two groups, the filter feeders and the deposit feeders. Filter feeders such as clams and quahogs filter their food by siphoning particles out of the water. Deposit feeders, such as snails and shrimp, ingest or sift through the sediment and consume organic matter within it.

Lady crab Lobster Winter flounder
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Before the age of deep-sea exploration scientists believed that there could be no life in the absence of energy from the sun. Since sunlight only penetrates the first 30m in coastal areas and 100m in the open ocean, they believed there was no life to be found on the ocean floor. What they did not realize was that there is a steady production of energy in the oceans in other forms than direct sunlight. One source of energy or food is the bodies of organisms that have died in the upper sunlit layers of the sea. They settle downward through the water column where they can be consumed. There is a constant vertical downflow of food or energy from the upper layers of the water to the benthic community.

Benthic animals are much more abundant in the shallower waters off the coast. In the shallow water the dead food material is more abundant because there is a higher population of organisms near the surface in this area. In these waters food also arrives from river sediments. Once food has reached the sea floor, currents carry this food and organisms filter it without having to use their own energy to go and get food. Another way organisms use energy is by coming out at night and rising to feed on upper-level organisms. Many large organisms are formed as they feed on microscopic food.


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


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