An Overview of Biological Indicators - From Protozoa to Fish

Defense Date


Document Type


Degree Name

M.S. Marine Biology

First Advisor

Donald McCorquodale

Second Advisor

A. Rogerson


Biological indicators are defined as “multiple measures of organism health to environmental stressors which include several levels of biological organization and time scales of response.” ( Oakridge National Laboratory). Indicators need to be better understood in order that they can be of greater use in the biological sciences. A fuller understanding of the relationships between living organisms and their surrounding environment will allow scientists to make better use of biological indicators. It is therefore imperative that we strive to understand the complex interactions that biological life has with the chemical and physical aspects of the world we all share. This is essential if we are to advance our current understanding of science to the next level for the benefit of all mankind. This area of study is an extremely complex topic that constantly needs to be narrowed down and studied using a reductionist approach. This paper adopts this view and for the purposes of unity and thoroughness the discussion will focus on the aquatic environment rather than the terrestrial environment.

The United States Congress passed the Clean Water Act over twenty-five years ago. Since its passing, this Act has done a lot of good but it has also left many unanswered questions in the scientific community. Many of these questions address the biological, physical, and chemical states of our nation’s waterways. This paper will give some direction to those unanswered questions. One approach to answering these questions is to look directly at the plants and animals that inhabit our waterways. By understanding the relationships that “biological indicators” have with their surrounding we can highlight problems or potential problems that would otherwise have been underestimated or missed completely (

It is well documented that environments may pose stressors on the organisms that inhabit them. This is the whole basis behind the use of biological indicators. Because these stressors occur, scientists must use multiple measure of health to help identify and separate the effects of natural stressors, such as food and shelter needs, from man made stressors, such as pollution ( Oakridge National Laboratory). “Biological indicators integrate, in themselves, the effects of various stressors, aquatic organisms and their communities reflect current conditions, as well as changes over time and cumulative effects” ( Why use biological indicators?). It is this general idea that led the Environmental Protection Agency to develop its ecological objective and goal of creating clean and safe waters. This objective sums up the significance of biological indicators for the scientific community. “Conserve and enhance the ecological health of the nation’s (state, interstate, and tribal) waters and aquatic ecosystems – rivers and streams, lakes, wetlands, estuaries, coastal areas, oceans, and groundwater – so that 75 percent of waters will support healthy aquatic communities by 2005” (

Shouldn’t observing and maintaining clean and healthy biological communities be the goal of every scientist and resource manager? By looking at the condition of these aquatic communities we can provide the basis for determining the ecological potential of a given community, and provide the means to measure how closely we have come to achieving that potential. Using the information that we gather from examining biological indicators we, as scientists, can achieve the following:

Bioassessment is assessing an area by looking at the biological, chemical, and physical relationships that occur with frequency, and quantitatively measuring the effects of these relationships on the biology of the area. A bioassessment essentially does three things:

  1. It uses information gathered directly from organism and the biological communities of which they are a part.
  2. Proclaims that the bioassessment organisms are shaped by all environmental factors to which they are exposed to over time.
  3. Combines multiple, community level, biological responses into a cumulative indicator of environmental impacts.

It is crucial that we fully develop and understand the place that biological indicators have in helping us, as scientists, to understand the world around us.

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