Bioindicator

Definition of Bioindicator: A bioindicator designates an animal, plant or a group of species, of which some vital functions are modified in response to certain pollutants. These species provide information about the cumulative effects of different pollutants in the ecosystem. This is the common definition for Bioindicator, other definitions can be discussed in the article

Bioindicators are early indicators of biotic or abiotic changes in the environment. Bioindicators are an important addition to the assessment of pollutant concentrations in water and/or sediment, because the bioindicator organisms only incorporate the bioavailable fraction of polluting substances persisting in their environment. A good bioindicator meets the following requirements:

• sessile or sedentary with a broad spatial and temporal distribution,
• easy to identify and collect,
• specific to a particular contaminant or a class of contaminants,
• sensitive enough to detect toxicity effects at an early stage prior to possible effects at high levels of biological organization,
• responds in a concentration-dependent manner to change in ambient levels of the contaminant,
• with small or known variability in response to non-toxicological environmental factors.

Different indicator types can be distinguished:

• sentinel species : give an indication, by their presence/absence, on the imbalances experienced by the environment,
• pollution indicator species : have adaptive mechanisms to (certain) pollutants and therefore dominate in the contaminated environment,
• bioaccumulator species : accumulate xenobiotics either by tissue concentration or by biomagnification through the food chain.

Four levels of bioindicator response to pollution can be observed:

1. Biointegration: response manifested by the presence of a certain species or by changes in their abundance.
2. Bioindication : presence of visible alterations at the individual or/and morphological and/or tissue scale.
3. Biomarker : presence of early infra-individual and invisible reactions, such as cellular or molecular alterations.
4. Bioaccumulation : the capacity of certain organisms to accumulate environmental pollutants.

Bioaccumulation can occur for pollutants that are not degradable and have a long persistence in marine ecosystems. These pollutants will be ingested by marine organisms, directly from the water or after being adsorbed to marine particles, such as sediment and plastic debris. Bioaccumulation depends on the liposoluble character and persistence of the molecule in the body. Persistent organic pollutants (POPs) are lipophilic in nature and can easily cross the biological membranes and accumulate in fatty tissues. Bioaccumulation of a pollutant takes place if the rate of intake exceeds the rate of excretion.

Marine bivalves (mussels, oysters, cockles) are the group of marine animals most widely used as bioindicators due to their ability to accumulate contaminants over a relatively long timespan. Bivalves are fairly resilient to changing environmental conditions and allow for the detection of negative impacts before they become irreversible. Their sessile, burrowing and filter-feeding lifestyle exposes them to a wide range of contaminants, including metals, persistent organic pollutants, pathogens, plastics and environmental changes caused by human activities. They therefore meet many of the requirements to be good bioindicators.

Related articles

Common biomarkers for the assessment of marine pollution

Biomonitoring of pollution impacts in the marine environment

Biomarker

Portal:Ecotox

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