Life at the Bottom

The organisms that live at the bottom of the Chesapeake Bay and its streams and rivers are known as benthos. Clams, worms, oysters and mussels are examples of benthic organisms. The word benthos comes from a Greek term meaning “depths of the sea.”

Benthic communities are complex and include a wide range of animals, plants and bacteria from all levels of the food web.

What types of benthic organisms live in the Chesapeake Bay?

There are two groups of benthic organisms, based on their habitat: epifauna and infauna. Epifauna live attached to a surface and infauna live within the Bay’s bottom sediments.

Epifauna

Epifauna live attached to hard surfaces such as rocks, shells and pilings. They also live directly on the surface of the Bay’s bottom. Epifauna include oysters, sponges, sea squirts, sea stars and barnacles.

An oyster reef is an example of an epifaunal benthic community.

Infauna

Infauna burrow into bottom sediments. Worms, clams and other infauna form their own communities that are connected to the water by tubes and tunnels.

The illustration below shows an example of a healthy infaunal community that contains many different species.

Why are benthic organisms important?

Benthos play several important roles in the food web. Benthic organisms are also an excellent indicator of environmental conditions in the Bay and its streams and rivers.

Benthic organisms form an important link in the food web

Benthos link the primary producers (phytoplankton) with higher levels in the food web.

• Filter feeders such as clams and oysters consume plankton and organic particles.
• Many benthic creatures, particularly clams and worms, serve as food for larger, economically important species such as blue crabs, striped bass, spot, croaker and white perch.

Additionally, the bacteria, decomposers and detritus-feeders that live at the Bay’s bottom break down waste products and dead plants and animals.

Benthic communities are an excellent environmental snapshot

Scientists study benthic organisms because they provide a good snapshot of environmental conditions in the Bay and its streams and rivers. Most benthic creatures cannot move very far, if at all, so they can’t avoid pollution or unhealthy water conditions.

Benthic communities are exposed to many stressors, including low oxygen levels, excess sediment and chemical contaminants.

• In summer, high temperatures and nutrient pollution often lead to low-oxygen areas at the bottom of the Bay and its rivers.
• Excess sediment suspended in the water can block sunlight from reaching bay grasses growing at the bottom. When sediment finally settles, it can bury oyster bars and other benthic species.
• Many chemical contaminants bind to bottom sediments, remaining there for years. Benthic species become contaminated when they feed and live in these toxic sediments.