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What is Benthic Habitat?

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The term benthic refers to anything associated with or occuring on the bottom of a body of water. The animals and plants that live on or in the bottom are known as the benthos. Benthic habitats can best be defined as bottom environments with distinct physical, geochemical, and biological characteristics. Benthic habitats vary widely depending upon their location and depth, and they are often characterized by dominant structural features and biological communities.

Marine benthic habitats are divided into zones based upon how deep they are in the water. From deepest to shallowest these include: the hadal zone (over 6,000 meters deep), the abyssal zone (2,000 to 6,000 meters), the bathyal zone (200 to 2,000 meters), and the nearshore and estuarine zones (less than 200 meters). Because the hadal, abyssal, and bathyal zones all occur in relatively deep ocean waters, benthic habitats in these zones have been much less commonly observed and mapped.

Estuarine and nearshore benthic habitats can be highly diverse, including shallow submerged mudflats, rippled sandflats, rocky hard-bottom habitats, seagrass beds, kelp forests, shellfish beds, and coral reefs.

An example illustration of different benthic habitats: (left to right) oyster bed, seagrass meadow, amphipod tube mat, sandflat. Courtesy: NOAA Coastal Services Center

Why are benthic habitats important?

Benthic habitats are important for a variety of reasons. Estuarine and nearshore benthic habitats support a wide diversity of marine life by providing spawning, nursery, refuge, and foraging grounds for fisheries species. They function in nutrient cycling, and contribute to the removal of contaminants from the water column. Benthic organisms are also important members of the lower food web, consuming organic matter and phytoplankton and serving as food sources for higher level consumers.

• Many benthic habitats (for example, coral reefs, eelgrass beds, and kelp forests) have three-dimensional structure that serve as shelter and provide storm protection by buffering wave action along coastlines.
• Benthic habitats can play an important role in maintaining water quality. Many benthic organisms, including filter feeders like hard clams, bay scallops, and mussels, obtain their food by taking in sea water. As the water flows through their bodies, sediments, organic matter, and pollutants are filtered out and ingested. This role makes these benthic communities good indicators of health in estuarine ecosystems.
• Benthic habitats play a critical role in the breakdown of organic matter, through the actions of scavengers, deposit-feeders, and bacteria.
• Many benthic organisms, such as amphipods and worms, and plants, such as widgeon grass, serve as important food sources for many species of fish, shellfish, and birds.

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