**3. Bioindicators concept**

In recent decades, the use of alternative biological activities for monitoring the state of the environment has been increased due to the high cost associated with traditional instrumental measurement methods. The use of bio-indicators is considerably more economical since it generally makes it possible to avoid using expensive technological equipment and to save time [20, 21]. Bio-indication therefore refers to a process of analysis of various biological indicators that is part of the biomonitoring of

### *Effect of Heavy Metal Pollution on Invertebrates DOI: http://dx.doi.org/10.5772/intechopen.109905*

the quality of ecosystems [22]. The indicators that can provide ideas on the qualitative state of the environment are defined as bioindicators. These bioindicators are frequently used in scientific investigations to assess the progressive impacts of pollutants due to anthropogenic activities. Bioindicators are sensitive to changes and disturbances in biotopes. However, the quality of an environment can be assessed by living species, which have an essential role in monitoring its disturbances [23]. Moreover, certain bio-indicators for their capacity of bioaccumulation, allow an early detection of pollutants or disturbances [24]. Furthermore, bio-indicators provide information "on the bioavailability of pollutants rather than on their total concentration in the environment" [20]. This distinction is significant when looking at the effects of pollutants on organisms [25]. Finally, unlike instrumental measurements which take parameter values instantaneously and locally, bio-indicators provide an integrated indication of the spatiotemporal effects of pollutants on biota since they "reflect the total time of exposure to the pollutant" [20]. According to [26], a bioindicator (or bio-indicator or biological indicator) is an organism or set of organisms which, by reference to biochemical, cytological, physiological, ethological or ecological variables, makes it possible, in a practical and safe way, to characterize the state of an ecosystem or an ecocomplex and to bring to light as early as possible their modifications, natural or provoked". The choice of indicator species is based on their easy monitoring, and that they can predict the conditions of the environment to which they belong [27]. In addition, indicator species must be easily collected, very abundant, widely distributed, available all year round, easily recognized by non-specialists, possess a high sensitivity to environmental constraints and should be profitable [3].
