The bioindicators they are biological processes, communities or species, which allow evaluating the quality of the environment and its dynamics over time. They are used to evaluate the impact of human activities on ecosystems, through the study of the response of biota to the stress generated.
We must consider that every activity generates an environmental impact that can be positive or negative. However, human activity has almost exclusively generated negative environmental impacts that affect ecosystems and their biota.
Among the environmental damages generated by human activities are pollution with emissions and industrial or urban solid waste, the depletion of natural resources due to overexploitation, among others..
All these impacts generate stress in the existing biota and for this reason they are called anthropogenic stressors, to differentiate them from natural stressors, such as periods of intense drought or variations in temperatures due to climatic effects.
The development and application of bioindicators emerged in the 1960s and since then their repertoire has expanded in the study of aquatic and terrestrial environments under the influence of anthropogenic stressors..
Bioindicators make it possible to monitor chemical-physical environmental changes, monitor ecological processes, directly or indirectly detect the existence of pollutants, and in general, detect environmental alterations..
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A bioindicator, be it a biological process, a community or a species, regardless of the type of environmental alteration that it measures, and the geographic region in question, must meet certain characteristics:
-It must be sensitive to disturbance or stress, but not die or disappear from it. A bioindicator species or community should have a moderate tolerance to environmental variability.
-It should be possible to measure your response to stress. Biological processes within an individual can also act as bioindicators.
-Your answer must be representative of that of the entire ecosystem, population or species.
-It must respond according to the degree of pollution or environmental degradation.
-It must be abundant and common, presenting an adequate population density in the specific area under study. In addition, it must be relatively stable, overcoming moderate climatic and environmental variations..
-There should be information on the bioindicator, a good understanding of its ecology and life history, and a well-documented and stable taxonomy. In addition, its sampling must be simple and inexpensive..
-It must have public, economic and commercial importance for other purposes.
In the case of using individuals as bioindicators, their age and genotypic variation must be considered. It should also be verified that other environmental factors do not interfere with the study and complete the information with environmental toxicological tests..
The classification of bioindicators varies according to the characteristics that are to be highlighted in the classification system. For example, we can classify bioindicators according to their complexity, into bioindicator species, communities or ecosystems. But we can also classify them according to the environment they monitor..
All existing species (or ensembles of species) can tolerate a limited range of physical, chemical and biological environmental conditions. This feature can be used to assess environmental quality.
For example, trout that live in cold water streams in the western United States, tolerate a temperature between 20 and 25 ° C, therefore, this thermal sensitivity can be used as a bioindicator of water temperature.
These same trout respond at the cellular level to temperature increases in the water (by burning and logging the surrounding forests). In these cases, they synthesize a heat shock protein that protects their cells from the effects of increased temperature..
The quantification of these heat shock proteins in this species makes it possible to measure the heat stress of trout, and indirectly evaluate the alteration of the environment due to the cutting and burning of the forests surrounding the body of water..
Entire communities that cover a wide variety of tolerance ranges to multiple environmental factors, can serve as bioindicators to assess the environmental condition from a complex and holistic approach. These studies involve the use of analysis of multiple environmental variables..
The loss of ecosystem services, such as clean water and air, plant pollinators, among others, is considered an indicator of the health of the ecosystem..
For example, the loss of bee species -which are pollinators- is considered an indicator of the loss of environmental health, since they are sensitive to the presence of heavy metals, pesticides and radioactive substances..
As indicated above, bioindicators can also be classified according to the environment from which they provide information. Following this classification, we have bioindicators of air, water and soil quality.
Among the bioindicators of air quality, are those organisms sensitive to variations in the concentration of certain gases.
For example, lichens (symbiotic associations between a fungus, microalgae and or cyanobacteria) and bryophytes, are very sensitive to atmospheric gases, because they absorb them through their body.
These organisms do not have a cuticle or roots and their high surface / volume ratio favors the absorption and accumulation of atmospheric pollutants, such as sulfur dioxide. Therefore, its disappearance in certain areas is an indicator of poor air quality..
On the other hand, there are also lichens (like Lecanora conizaeoides), whose presence is indicative of poor air quality.
This sensitivity is due to the fact that canaries have low lung capacity and a unidirectional ventilation system. For this reason, canaries are much more sensitive than humans to harmful gases.
Among the bioindicators of water quality are bacterial microorganisms, protozoa, macroinvertebrates, algae and mosses, among others; sensitive to the presence of toxic pollutants.
For example, the presence of communities of different aquatic macroinvertebrate taxa in a river is an ecological and biodiversity indicator. The greater the number of taxa present, the greater the health of the body of water.
Other bioindicators of the state of rivers are otters, as they quickly leave bodies of water with low amounts of pollutants. Its presence then indicates the good condition of the river.
Marine sponges have also been used as bioindicators of heavy metals, such as mercury and cadmium, fecal substances, among others. The detection of the disappearance of sponges in marine waters is an indicator of the loss of water quality.
The presence in a water body of algae in dense concentrations is indicative of high levels of dissolved phosphorus and nitrogen, which can come from fertilizers dumped into the water. The discharged fertilizers generate the accumulation of their nutrients and the eutrophication of the aqueous medium.
As indicators of soil quality we can mention part of the biota of this habitat, that is, some plants, fungi and bacterial microorganisms..
If they present specific requirements for their survival, these organisms would be indicators of the existence of these conditions..
For example, earthworms are bioindicators of soil quality, since some species, such as Fetid eisenia Y E. andrei, They are sensitive to pesticides, oil derivatives, heavy metals, among others. These bioindicators are used in soil toxicity studies.
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