The lower food web includes the benthic (plants and animals that live at the bottom of the Bay) and the plankton (free-floating plants and animals that inhabit the water column) communities. The plankton community is composed of phytoplankton and zooplankton. Phytoplankton are microscopic plants, such as algae, which are the major primary producers of the Bay. Zooplankton are small animals that consume plankton and in turn are consumed by higher organisms. They are the most plentiful animal in the Bay and its rivers. One gallon of water can contain more than a half-million zooplankton, ranging in size from tiny single-celled protozoa to jellyfish. All fish depend on zooplankton for food during their larval phases, and some species continue to consume zooplankton their entire lives. A herring may consume thousands of copepods (small crustaceans) in a single day.

Benthic organisms are members of the lower food web that have adapted to life on the bottom. Benthic organisms are varied communities of plants, animals and bacteria that live on rocks or other hard substrates, or in the mud and sediment of the Bay bottom. Benthic primary producers include macrophytes, or large algae, and emergent vascular plants (submerged aquatic vegetation, or SAV). Benthic consumers are diverse groups of animals that include mollusks and worms, which in turn provide food for the higher trophic orders.

Members of the entire lower food web, both the plankton and benthic communities, are important indicators of the health of the Chesapeake Bay. Plankton are known to be direct indicators of nutrient (nitrogen and phosphorous) conditions in the water column. Benthos and zooplankton are vulnerable to the stresses associated with toxic pollution, excess nutrients, low oxygen and high sediment concentrations in the water column. The continued analysis of benthic and plankton communities and their interactions with higher trophic levels are useful tools for Bay managers and scientists to help assess the status and trends in water and habitat quality, and to help understand how they continue to affect the Bay’s living resources.

Benthos image courtesy: Janet Nestlerode / VIMS

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Last modified: 12/11/03