Indicator Species

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What is Indicator Species?

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The word "bioindicator" is used to refer to all sources of biotic and abiotic responses to environmental changes. Taxa are used to display the effects of natural surrounding changes, or environmental change, rather than simply as gauges of natural change. They are used to detect changes in the natural environment and to show negative or positive effects. They can also detect changes in the ecosystem caused by pollutants, which can have an effect on the environment's biodiversity as well as the animals that live there.

In various species occupying various types of habitats, natural, biological, and biodiversity markers can be identified. Air pollution is often monitored using lichens and bryophytes (liverworts). Since they have no roots, no fingernail skin, and obtain all of their nutrients from immediate exposure to the climate, lichens and bryophytes are important bioindicators of air quality. Their high surface area to volume ratio adds to the hypothesis that they could be used as a bioindicator or to capture contaminants from the air. Cyanophyta, a form of phytoplankton, is a powerful bioindicator that can indicate rapid eutrophication of water bodies such as rivers, lakes, and other bodies of water by forming bloom formations.

Not all biological processes, plants, or populations, on the other hand, can be used as bioindicators. Environments differ in terms of physical, chemical, and biological influences. Populations develop strategies to optimise growth and reproduction within a limited range of environmental factors over time. Individuals' physiology and/or behaviour can be adversely affected outside of their environmental optima, or tolerance range, decreasing their overall fitness. Reduced fitness can cause population dynamics to shift and the society as a whole to change. Because of their moderate tolerance for environmental variability, bioindicator species effectively show the condition of the environment. Rare species (or species assemblages) with narrow tolerances, on the other hand, are often too sensitive to environmental change or too uncommon to represent the general biotic response. Similarly, widespread species with broad tolerances are less vulnerable to environmental changes that would otherwise disrupt the population. The use of bioindicators, on the other hand, is not limited to a single species with a narrow range of environmental tolerance. In a "biotic index" or "multimetric" approach, whole populations may serve as bioindicators and represent various sources of data to measure environmental conditions, encompassing a wide range of environmental tolerances.

Types of Indicator Species

Indicator species come in a variety of types. Bacteria to more complex organisms like plants and animals may all be used as indicator species. Although all have evolved to exist within certain limits, all species are indicators of something; many are especially sensitive and provide an early indication of changes in environmental conditions.

1. The Wood Stork 

The absence of wood storks in everglade habitats indicates that the climate is not conducive to abundant wading birdlife. Wood storks used to live in these wetlands by consuming small freshwater fish. Wood storks are held up as a model for the health of the Everglades by conservationists. The success of water-management restoration efforts on wood stork populations will help determine whether efforts are improving overall everglade conditions to support all bird, fish, animal, and plant life.

2. River Otters 

Crayfish and fish are the main foods of river otters, but they also eat other invertebrates, amphibians, and smaller mammals. Otters are one of the most common keystone species and apex predators, so if there is a problem lower down the food chain, they are usually the first to suffer. River otter reintroduction effectiveness has been used to evaluate the health of freshwater habitats. The health of river otters has also been used to assess mercury emissions in the ecosystem. Chemicals or heavy metals accumulate in an organism over time, which is known as bioaccumulation. River otters will likely be the first to show signs of mercury poisoning because they are at the top of the food chain.

3. Frogs

Frogs have semi-permeable skin that needs to stay moist in order to breathe. Since they are susceptible to consuming chemical pollutants in their water, their skin makes them bioindicators for the health of their environment. Many frogs have life cycles that use both terrestrial and freshwater habitats, making them vulnerable to environmental stressors including temperature changes and UV radiation.

4. Buck's Horn Plantain 

Salt exclusion and cellular osmotic adjustment are two mechanisms evolved by some plant species to cope with salt in the soil. Plants that lack these mechanisms would be unable to thrive in high-salinity environments. Buck's horn plantain is a good ecological indicator of salt levels in Australian soils because its leaves turn redder as the salt level rises.

5. Algal Blooms are Water Pollution Indicator Species

Algal blooms may be a sign of a changing climate. Algal blooms may be caused by a rise in nutrients from sedimentation runoff. Natural seasonal changes in nutrient availability can also be linked to algal blooms. The abundance of algae in a given area can also be used to detect nutrient availability gradients in a body of water.

6. Lichens as Bioindicators

Lichens are pollution indicators. Lichens are made up of a variety of fungi, algae, and bacteria. Lichens exhibit a variety of functional traits and responses in response to air pollution and temperature, making them a bioindicator of air pollution. As a result, the presence of various forms of lichens may be used to determine the environmental effects of urbanisation. For example, lichens made of chloro coccoid green algae and those with foliose narrow lobes are associated with medium to high levels of urbanisation. Low-density urbanised areas, on the other hand, have more cyanolichens and Trentepohlia algae lichens that have a crustose formation.

Bioaccumulator Indicator Species

Bioaccumulator indicator organisms are those that can avoid and accumulate different pollutant substances in their tissues, allowing them to be detected at very low levels in the atmosphere. The main disadvantage is that a variety of biotic and abiotic variables will influence the rate at which the pollutant accumulates, necessitating both laboratory and field testing to identify the effects of extraneous parameters.

Mollusks, especially bivalves, have long been the most common species used to detect the presence and quantity of toxic substances. Because of their sessile existence, vast geographical range, and capacity to absorb toxic substances in their tissues and detoxify when pollution ceases, individuals of the genera Mytilus, for example, have been considered ideal in many works to detect the concentration of toxic substances in the atmosphere.

Similarly, polychaete species such as Nereis diversicolor, Neanthes arenaceodentata, Glycera alba, Tharix marioni, or Nephtys hombergii are thought to be capable of accumulating toxic substances. Because of their bioaccumulative potential and the current relationship between pathologies experienced by any benthic fish and the existence of polluting substances, several fish species have also been used in various works focusing on the effects of toxic contamination of the marine environment.

Heavy metals, chemicals, and radionuclides have all been detected in algae, with Fucus, Ascophyllum, and Enteromorpha being the most commonly used taxa.

Bioindicators of Water Pollution

Plankton is responsible for a considerable amount of biological production in many water bodies, including oceans, lakes, streams, and swamps. Planktons are made up of chlorophyll-producing species. These planktons are made up of populations that move along with the rivers and tides, fusing and cycling large amounts of energy that is then passed on to higher trophic levels.

Planktons were studied in Indian lentic ecosystems in the mid-twentieth century. These studies showed that the dominant planktons and their regularity vary greatly in different water bodies depending on supplement status, age, morphometry, and other location factors. As a result, they're often used as markers of lake trophic status. Planktons respond quickly to environmental changes and are regarded as excellent indicators of water quality and trophic conditions due to their short lifespan and rapid reproduction rate. The resistance range in relation to abiotic ecological components (Temperature, Oxygen fixation, and pH) as well as biotic connections among organisms are used to identify the occurrence of planktonic organisms in natural conditions. The changes that occur within planktonic populations provide the foundation for determining the trophic condition of water bodies.

Benefits and Disadvantages of Bioindicators

Bioindicators' various advantages have prompted regulatory requirements for their use in countries all over the world, as well as their inclusion in a number of international agreements. Bioindicators, however, are not without flaws. We depend on the sensitivity of certain bioindicators to act as early-warning signals, just like the canaries in the coal mine. We can't always tell the difference between natural variations and changes caused by humans, which limits the applicability of bioindicators in complex ecosystems. As a result, factors other than disturbance or stress may have an effect on indicator species populations, complicating our understanding of the causal mechanisms of transition. The ability of bioindicators to serve as indicators is scale-dependent, according to the second criticism of their use. A large vertebrate indicator, for example, may not accurately represent the biodiversity of the local insect population. The habitat requirements of bioindicator species are invariably different from those of other species in their environment. Ecosystem management based on a bioindicator's habitat requirements which fail to protect rare species with different requirements. The ultimate objective of bioindicators is to determine the nature of an ecosystem and how it evolves over time using a single species or a small group of species, but this can be a gross oversimplification of a complex system.

We must be aware of its shortcomings, as with all management methods. Bioindicators' drawbacks, on the other hand, are obviously outweighed by their advantages. Bioindicators may be used to assess the health of an environment at a variety of scales, from the cellular to the ecosystem level. They put together data from our world's biological, physical, and chemical components to show how changes in human fitness, population density, community structure, and ecosystem processes manifest themselves. In terms of management, bioindicators help us determine what is and is not biologically viable. We do not understand the effect of our disruptions until it is too late to avoid them without the moss in the tundra, the cutthroat in the mountain stream, and the canary in the coal mine.


There are three different definitions for the word "indicator species." They are a species (or a group of species) that represent the biotic or abiotic state of an ecosystem, show evidence for, or the effects of, environmental change, or indicate the diversity of other species, taxa, or entire communities within a given region. The first two uses of indicator species are very similar, with the only difference being that organisms must be sampled more than once in the same location and in the same way to show change. Detecting emissions to tracking the regeneration of formerly damaged ecosystems, using species to show the condition of, and changes in, the ecosystem has various tried and tested applications at many scales, from local to global. The use of indicator species to estimate the diversity of other, unstudied taxa for scientific or conservation purposes is much more controversial, and it may prove difficult to do so with any degree of accuracy.

FAQ (Frequently Asked Questions)

1. What are “Indicator Species”?

Ans: Indicator Species definition is that they are living organisms such as plants, planktons, livestock, and microbes are used as bioindicators to monitor the health of the natural ecosystem throughout the environment. They are used to measure environmental health as well as biogeographic changes in the climate. Each organic organism within a biological system provides information about the health of its surroundings, such as plankton, which responds quickly to changes in the environment and serves as an effective biomarker for evaluating water quality and as an indicator of water pollution.

2. How is the Lichen Pollution Indicator?

Ans: Bryophytes (liverworts) and lichens (a symbiosis among Cyanobacteria, algae, and/or fungi) are commonly used to monitor air pollution. Since they have no roots, no fingernail skin, and obtain all of their nutrients from immediate exposure to the climate, lichens and bryophytes are important bioindicators of air quality. Their high surface area to volume ratio adds to the hypothesis that they could be used as a bioindicator or to capture contaminants from the air. Hence, lichen is a bioindicator of air pollution.

3. What Makes a Good Bioindicator?

Ans: In comparison to rare and common animals, bioindicators have a moderate tolerance for environmental variability. This tolerance allows them to be sensitive to environmental change while still having the endurance to withstand some variability and represent the biotic response as a whole. They should have the following qualities to make a good Bioindicator:

  • Offer a measurable response. 

  • The response represents the reaction of the entire population, community, and environment.

  • Respond in proportion to the level of pollution or degradation.