Bioindicators – mechanism, uses, advantages and examples

What are bioindicators?

A bioindicator is a living organism that gives us an idea of the health of an ecosystem. Some organisms are very sensitive to pollution in their environment, so if pollutants are present, the organism may change its morphology, physiology or behaviour, or it could even die.


What can be a bioindicator?

Bioindicators can be plants, animals or microorganisms.


How various bioindicators tell about the environmental health?

1. If toxins are present, certain plants may not be able to grow in the area affected.

2. Monitoring population numbers of animals may indicate damage to the ecosystem in which they live.

3. Algae blooms are often used to indicate large increases of nitrates and phosphates in lakes and rivers.

4. If pollution causes the reduction of an important food source, the animals dependent on it for food may also decrease. Animals may also change their behaviour or physiology if a toxin is present.

5. The levels of certain liver enzymes in fish increase if they are exposed to pollutants in the water.

6. Changes in the functioning of the nervous systems of worms are used to measure levels of soil pollution.

7. The increase in the number of mutated frogs found in the USA is used as an indicator of toxins in their environment.

8. Microorganisms can also be used as indicators of toxins in an ecosystem. Some microorganisms will produce stress proteins if exposed to certain pollutants. By measuring the levels of stress proteins, we can get an idea of the level of pollution present in the environment.


Lichens – The most well know bioindicator

What are lichens?

A lichen is a composite organism that arises from algae or cyanobacteria (or both) living among filaments of a fungus in a mutually beneficial relationship (symbiotoc relationship).

The hardy lichens are useful bioindicators for air pollution, especially sulfur dioxide pollution.


How are lichens able to act as bioindicators?

1. Lichens live on surfaces such as trees or rocks or soil and are very sensitive to toxins in the air.

2. They have no roots, no cuticle, and acquire all their nutrients from direct exposure to the atmosphere rather than from the soil.

3. Their high surface area to volume ratio further encourages the interception and accumulation of contaminants from the air.

4. they are able to react to air pollutants all year round.

5. Compared with most physical/chemical monitors, they are inexpensive to use in evaluating air pollution.


Frogs as bioindicators

1. Most frogs require suitable habitat in both the terrestrial and aquatic environments, and have permeable skin that can easily absorb toxic chemicals.

2. These traits make frogs especially susceptible to environmental disturbances, and thus frogs are considered accurate indicators of environmental stress: the health of frogs is thought to be indicative of the health of the biosphere as a whole.


Aquatic insects and other macroinvertebrates as indicator of water quality

They are preferred bioindicator for measuring water quality because –

1. Aquatic macroinvertebrates are found in nearly every body of inland (non-marine) water, so they are ubiquitous.

2. They are easy to collect compared to a lot of other things like fishes.

3. They live in the water all the time and are reasonably long-lived. Pollution can and sometimes does occur steadily over time (imagine a wastewater treatment plant outfall or a paper mill dumping waste into a river). Sometimes, every trace of the pollutant has disappeared from the water by the time a researcher can collect a water sample from the stream. However, many of the insects were in the stream during the pollution event! This means that, even if you can no longer find the pollutant in the water, or never even knew a pollution event occurred, the organisms in the stream can show you that something is wrong.


Bioindicators and biomonitors

Bioindicators qualitatively assesses biotic responses to environmental stress (e.g., presence of the lichen indicates poor air quality) while biomonitors quantitatively determine a response (e.g., reductions in lichen chlorophyll content or diversity indicates the presence and severity of air pollution).


Why Are Bioindicators Better Than Traditional Methods?

1. Bioindicators add a temporal component corresponding to the life span or residence time of an organism in a particular system, allowing the integration of current, past, or future environmental conditions. In contrast, many chemical and physical measurements only characterize conditions at the time of sampling, increasing the probability of missing sporadic pulses of pollutants.

2. Bioindicators can indicate indirect biotic effects of pollutants when many physical or chemical measurements cannot.

3. Given the thousands of substances and factors to monitor, scientists now understand that the biota itself is the best predictor of how ecosystems respond to disturbance or the presence of a stressor.

4. In most cases they are inexpensive compared to chemical methods.


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