Chesapeake Bay Benthic Monitoring Program

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Assemblage:  A group of animals or plants occurring together in a particular location or region.

Benthic: Refers to benthos.

Benthic Grab: Device designed to collect bottom sediment samples. Different types of benthic grabs are used. Most consist of a pair of hinged jaws and a lever system with a release catch that allows the jaws to close on the bottom. The Chesapeake Bay Monitoring Programs use a Young grab that samples an area of sediment of 440 squared centimeters.

Benthic Index: A parameter or formula that describes in a single number the relative health of the benthic community.

Benthic Invertebrate: Animal without a backbone that lives on or below the surface of the sea bottom .

Benthos: Animals and plants associated with the sea bottom.

Biomass: Amount of living matter per unit area.

Biotic Integrity: The ability to support and maintain a balanced, integrated, adaptive community with a biological diversity, composition, and functional organization comparable to those of natural aquatic ecosystems in the region.

Diversity Index: A parameter or formula that describes in a single number the different types and amounts of animals present in a collection.

Epifauna: Animals living on the surface of sea bottom sediments, usually associated with surface structures such as rocks, shells, vegetation, or colonies of other animals.

Equilibrium species: Large, relatively long-lived species whose presence often indicate undisturbed conditions.

Hard bottoms: Sea bottom consisting of a hard substrate such as rock.

Indicator: Species whose presence in the community are reflective of the relative condition of the environment.

Infauna: Animals living below the surface of sea bottom sediments. They usually burrow or build tubes in the sediment.

Invertebrate: Animal without a backbone .

Macrofauna: Animals retained on a 0.5 millimeter mesh sieve.

Meiofauna: Animals passing a 0.5 millimeter mesh sieve but retained on a 0.062 millimeter mesh sieve. This is the size of the smallest grain of sand.

Megafauna: Large, motile bottom-dwelling animals such as Blue Crabs and flat fish.

Monitoring: Continuous assessment of the environment to determine seasonal and annual variability and trends.

Mud: Sediment consisting of mineral particles mostly smaller than 0.062 millimeters.

Opportunistic species: Species that colonize disturbed or polluted sediments. These species are often small, grow rapidly, have short life spans, and produce many offspring .

Parts per thousand: Salinity unit indicating grams of salts per kilogram of sea water (g/kg) .

Phytoplankton: Organisms that are part of the plankton and are photosynthetic, meaning that they utilize the energy from light to grow.

Plankton: Organisms that live in the water column and are passively carried by the currents.

Pollution-indicative: Species that are tolerant of pollution.

Pollution-sensitive: Species that are sensitive to pollution.

Sand: Sediment consisting of mineral particles in the range of 0.062 to 2.0 millimeters.

Shannon-Wiener Diversity Index: A diversity index that describes in a single number the different types and amounts of animals present in a collection.  Shannon-Wiener varies with both the number of species and the relative distribution of individual organisms among the species.  The index ranges from 0 for communities containing a single species to high values for communities containing many species and each with a small number of individuals.

Soft bottom: Sea bottom consisting of sediments such as mud or sand.


Methods and
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Revised: March 20, 2003.