Biological Indicators in Different Environments

Terrestrial environment: A brief outline

From the bacteria to the vertebrates, a large amount of species have been utilized. Nevertheless, it is among the plants where valuable indicators have been found. More often, plant assemblages are the most useful in informing about the general conditions of an environment, from its past to its future. The phytosociological approach is demonstrative. Invertebrates, nematodes, oligochaete worms, and insects are among the most frequently used. Birds also merit a special attention, but they could give their most useful indications at higher levels of ecosystems.

Continental waters: An outline

The use of organisms to judge the state of continental aquatic ecosystems is as old as a century ('Saprobies' method). This method evolved till present, with substantial modifications. It is no longer used to only detect the level of organic pollution in streams and lakes. Macrobenthic invertebrates (oligochaetes, mollusks, and arthropods) are the most favorite indicator species. Innumerable researches have demonstrated the effects of pollution and other disturbances on the modifications of the faunal structure of communities and have proposed numerous diagnostic methods. Zoological groups are classified according to their sensibility (or their resistance) to pollutants and the influence of the morphology and dynamics of the environment on the community at the sampling point. Presence of Plecopteres and Trichopteres is considered as an indicator of 'good' environments, whereas Tubificidae and Chirominae are indicative of 'bad' environments.

Marine waters

The seas represent 75% of the Earth's surface, which is one of the reasons why the approach of biological indicators in marine environment is preferable here. This choice is based on the diversity at the higher levels of marine animals, their exclusive presence for there are numerous of them; the great diversity of habitats; and the fact that, ultimately, all pollutants join the sea.

The study of the Los Angeles and Long Beach harbors more than four decades ago is generally considered as the cornerstone of the description of biological indicators and animal communities in marine polluted environments. Few years later, a similar group of indicators of disturbance in soft-bottom communities at the sea-exit of the big sewer of Marseilles (northern Mediterranean Sea) and inside its harbors was proposed. One distinguishes

1. a 'maximum polluted zone', azoic in term of macro-benthos;

2. a 'polluted zone', oligospecific with a very reduced number of species;

3. a 'subnormal' or 'intermediate zone' characterized by the disappearing of the precedent species and the dominance of a restricted number of species monopolizing the space and considered as 'sentinels' of this intermediate zone; and

4. a 'normal zone', consistent with the 'unaffected' communities encountered in the corresponding geographical zone.

These zones and subzones are clearly related with amounts of pollutants, especially organic matter and levels of physical variables in the sediment.

Such a schema is recognized throughout the European and Mediterranean seas. It is also in perfect concordance with similar studies along the Californian coast.

In the 1980s, a certain number of specialists considered these methods to discriminate biological indicators as being too subjective and did not sound in tune with recent advances in theoretical ecology. Based on the observations that tolerant species are predominantly found in disturbed environments, that is, they mainly occur at stations with low number of species, and sensitive species are present in stations with no or minor disturbances, several authors tried to obtain more 'objective' indicators. For this purpose, using the listing of species, they proposed a method based on the use of 'probit' transformation of log-normal series (Preston's model). Later, the determination of such tolerant or sensitive species has

Figure 2 Examples of total abundance frequency distributions of the pioneer colonizer Capitella capitata and the frequently occurring Amphiura filiformis in relation to their ES50 values. The most tolerant individuals are associated with the lowest ES50 values. This gives the tolerance value: ES500 05. Shaded portion represents 5% abundance in relation to lowest ES50 values. Modified from Rosenberg R, Blomqvist M, Nilsson HC, Cederwall H, and Dimming A (2004) Marine quality assessment by use of benthic species-abundance distributions: A proposed new protocol within the European Union Water Framework Directive. Marine Pollution Bulletin, with permission from Elsevier.

ES50

Figure 2 Examples of total abundance frequency distributions of the pioneer colonizer Capitella capitata and the frequently occurring Amphiura filiformis in relation to their ES50 values. The most tolerant individuals are associated with the lowest ES50 values. This gives the tolerance value: ES500 05. Shaded portion represents 5% abundance in relation to lowest ES50 values. Modified from Rosenberg R, Blomqvist M, Nilsson HC, Cederwall H, and Dimming A (2004) Marine quality assessment by use of benthic species-abundance distributions: A proposed new protocol within the European Union Water Framework Directive. Marine Pollution Bulletin, with permission from Elsevier.

been proposed according the Hurlbert's formula and recently reassessed. Figure 2 presents an example to show the abundance distribution patterns of two species, Capitella capitata and Amphiura filiformis, of great relevance in disturbed environments.

The selection of these indicators is 'subjective' or 'objective'. To be effective, their use needs an optimum knowledge in systematics and great competence in the ecology and ethology of the chosen species.

If invertebrates have mostly interested specialists of marine pollution, it is well recognized that the phyto-benthos could be very sensitive (or not) to polluted waters. If Phaeophyta are rather sensitive (based on the correlation of the disappearance of Cystoseira amentacea stricta along a gradient of detergents in Marseilles area), Chlorophyta could be rather tolerant and Rhodophyta could have diverse requirements.

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