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Benthic Habitat Mapping

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Applying Benthic Data: Habitat Quality Assessment

Summary

Overlapping circles

Diagram showing the relationship among environmental tolerances, species preferences, and substrate characteristics to define habitat.
Adapted from Diaz, Solan, and Valente 2004.

Seabed-mapping technologies help generate benthic habitat maps that are useful for assessing the state of living resources. The key to successful application, however, lies in the translation of basic physical data of bottom characteristics into meaningful representations of benthic habitat quality. Benthic habitat is defined as submerged bottom environments with distinct physical, geochemical, and biological characteristics. Thus, the concept of habitat quality incorporates aspects of the physical substrate as they pertain to living organisms.

Since marine benthos research often details organism-sediment interactions, many investigators equate the concept of benthic habitat with bottom sediment or substrate type. This is intuitive because the habitat occupied by benthic organisms is the sedimentary environment. However, this simplistic view has lead to a great deal of confusion as to the definition of habitat. This perspective equates habitat only with the seafloor topography plus sediment textural characteristics. These physical properties and dynamics of the bottom exist, in most cases, independent of biological processes. Substrate becomes habitat only when the intricacies of specified organisms are introduced.

Habitat quality and structural indices are an important means for assigning a quality measure to different locations and times within or between habitats. The Chesapeake Bay Program provides an example of what is required to make the transition from seabed mapping to a benthic quality assessment. One of the goals of the Chesapeake Bay Program is to determine the percentage of Chesapeake Bay and its tributaries that have degraded infaunal community structure. To meet this goal, two basic types of data are needed:

Habitat quality map

Map of benthic condition in a portion of the Chesapeake Bay based on 2001 data.
Courtesy: Chesapeake Bay Program

  1. Unbiased data on infauna community structure, substrate characteristics, and water quality from around the Bay (Dauer et al. 2000). Such data can be used to identify locations having degraded or stressful benthic habitat conditions (e.g. low dissolved oxygen levels in near-bottom waters, elevated chemical contaminants in sediments) versus "reference" locations that are relatively undisturbed benthic habitat quality.

  2. A metric for assessing infaunal conditions relative to substrate and water quality (Weisberg et al. 1997). This refers to the development of a "Benthic Index of Biotic Integrity (B-IBI)" - a single number or value designed to reflect the degree to which the structure of the benthic community (i.e. the types and numbers of organisms present) in a given location has been affected by degraded habitat conditions compared to undisturbed or "reference" conditions.

When data from 1 and 2 are combined into a predictive model of infaunal conditions then benthic habitat quality can be assessed and mapped. The Benthic Indices page describes those that have been developed specifically to evaluate estuarine and marine benthic habitats. The Regional Monitoring case study describes an example of how these indices are incorporated in regional quality assessments for resource management.

References

Dauer, D.M., S.B. Weisberg, and J.A. Ranasinghe. 2000. "Relationships Between Benthic Community Condition, Water Quality, Sediment Quality, Nutrient Loads and Land Use Patterns in Chesapeake Bay." Estuaries. Volume 23. Pages 80 to 96.

Diaz, R.J., M. Solan, and R.M. Valente. 2004. "A Review of Approaches for Classifying Benthic Habitats and Evaluating Habitat Quality." Journal of Environmental Management. Volume 73. Pages 165 to 181.

Weisberg, S.B., J.A. Ranasinghe, D.M. Dauer, L.C. Schaffner, R.J. Diaz, and J.B. Frithsen. 1997. "An Estuarine Benthic Index of Biotic Integrity (B-IBI) for Chesapeake Bay." Estuaries. Volume 20. Pages 149 to 158.

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