Subjective versus objective index

In the context of national and international regulations, a certain number of new indicators and indices have been proposed.

Among them, this review focuses on Benthic Quality Indices (BQJ) build up to establish the quality of European coasts, investigating the response of soft-bottom communities to natural and man-induced changes.

AMBI is based upon ecological models proposed previously by several European ecologists. The theoretical basis is that of ecological adaptive strategies and the progressive response of benthic communities to increasing gradients of impact in stressed environments. The index requires classifying the species into five ecological groups (EGs), which are in relation to the different responses of benthic species to pollution or disturbance (from very sensitive to pollution to opportunistic responses). This pattern is related to the r, k, and t models. These models seem to have been greatly enhanced by the AMBI as a new tool. AMBI is a formula, that compares the proportion of the abundance of each EG within a sample, permitting the derivation of continuous values, which allows for further statistical analyses. Several thresholds in the AMBI scale were established based upon the proportions among the five EGs. These thresholds coincide with the benthic community health proposed by numerous authors for more than four decades. AMBI has been verified under a very large set of impact sources (including drill cutting discharges, submarine outfalls, harbor and dyke construction, heavy metal inputs, eutrophication, engineering works, diffuse pollutant inputs, recovery in polluted systems under the impact of sewerage schemes, dredging processes, mud disposal, sand extraction, oil spills, fish farming, etc.) as well as in various geographical areas (Europe, South America, Africa, and Asia). The AMBI has several advantages, such as its general ecological theoretical basis (which makes it potentially utilizable everywhere); the free software together with the continuously updated species-list (currently it has over 3500 taxa); the clear guidelines in its utilization; its validation under different impact sources; and the easy use and 'visual' results for politicians, stakeholders, and public in general. However, there are also problems in its use, which have been outlined by the authors. One of the problems currently encountered with this kind of indices is linked with the classification of the species into different EGs. It is eventually necessary to check carefully the pertinence of the general classification with the local environmental conditions and if needed, to add new local species. As an example of its utilization, the Cortiou-Marseille (French Mediterranean) submarine outfall has been used in this review. This outfall has discharged at a rate of around 90 million m3 of treated water/year for at least last 50 years. Figure 3 shows the mean AMBI values over the area. Near the outfall (Cortiou) AMBI values range between 5.3 and 5.99: this means that the area is highly disturbed, with the dominance (55-99%) of EG V (which includes species as Capitella capitata) and EG IV (until 46%), both EGs being composed of opportunistic species. Then there is an area moderately disturbed (with AMBI values ranging between 3.32 and 4.91), dominated by second-order opportunistic species (EG IV until 66%) or a mixture of EGs III, IV, and V. The slightly disturbed zone, with AMBI values between 1.26 and 3.01, extends northwestwards and southeastwards, which are the main directions of the currents within the Cortiou area. The transport of some of the pollutants modifies the community composition over the area, dominated mainly by EG II and the presence of EGs III and IV. Finally, the remainder of the area is undisturbed (AMBI values between 0.09 and 1.19), dominated by EGs I (sensitive to pollution) and II. This area coincides with some protected coastal locations, which are unaffected by the outfall discharges. These conclusions are in accordance with local expert judgment and their long-time knowledge of the area.

Another index ('BENTIX Index') has been presented with data from Greek and western Mediterranean for approaching the objective of Ecological Quality Status along the lines of the European Water Framework Directive. Otherwise, this BENTIX index could also be applied with the regulations from the Mediterranean Barcelona Convention. Both the theoretical basis and the development of BENTIX appear similar to AMBI. Nevertheless, it presents differences in its biogeographi-cal scope (Mediterranean Sea) and some modalities of its development. BENTIX is typically Mediterranean. The choice and the evaluation of the benthic indicators are defined from the major soft-bottom communities in Mediterranean through experience and review of relevant literature. The scoring of indicator groups introduces an appreciable change in the methodology. The basic concept of BENTIX lies in the reduction of EGs involved in the formula: limited to three. As regards the groups, they include species 'sensitive' to disturbance in general, group 1 (GI) scoring 1; 'tolerant' to disturbance or stress and 'second-order opportunistic' species group 2 (GII) scoring 2; and 'first-order opportunistic' species group 3 (GIII) scoring 3. The formula obtained is: BENTIX = {6 x %GI + 2 x (%GII + %GIII)}/100. The limits of the scale are set from 2 to 6 (being 0 when the sediment is azoic). A classification scheme of soft-bottom benthic habitats based on BENTIX index has been provided in Table 1.

In order to check its effectiveness, BENTIX has been validated with respect to some water quality parameters and various tools of classification of communities. It has been tested with success mostly in northeastern Mediterranean.

Two other indices rather similar to their precedents were tested in western Mediterranean, in north (Marseilles) and south (Algiers) to determine the 'state of the marine environment quality'. It proposed two indices: an 'index of quality of the environment (Ind.

Table 1 A classification scheme of the soft-bottom benthic habitats





quality status


4.5 < BENTIX <6.0


Slightly polluted,


4.5 < BENTIX <4.5




2.5 < BENTIX<3.5


Heavily polluted

2.0 < BENTIX<2.5





Qual.)' and a 'pollution-Degradation one (Ind. Poll.-Degr)'. These indices are based on the percentage of six groups of sentinel, indicative, or characteristic species. These groups are affected with a particular factor, according to their sensibility or their resistance to pollution (Table 2).

As in AMBI and BENTIX, a similar formula, permitting the derivation of continuous values, allows statistical analyses. Groups are assigned with an increasing factor from 1 to 6 for Ind. Qual. and computed according to the formula: Ind. Qual. = (1 x %IP1 + 2 x %IP2 + 3 x %Opp1 + 4 x Opp2 + 5 x %Sed. + 6 x %

Bioc). Alternatively, these groups are assigned with a decreasing factor from 6 to 1 for Ind. Poll.-Degr. one: Ind. Poll.-Degr. = (6 x %IP1 + 5 x %IP2 + 4 x %Opp1 + 3 x Opp2 + 2 x %Sed. + 1 x %Bioc).

According to obtained indices, the environment could be qualified as such (see Figure 3) and compared with AMBI (Table 3).

For the assessment of environmental quality at a particular station, a BQI has been recently proposed and discussed. One of its best interests lies in its good correlation with an earlier paper on classifying the distribution patterns of pollution-tolerant invertebrates (Figure 4) in the same area. The BQI is calculated as where A is the mean relative abundance of a species (i) and S the mean number of species at the considered station. BQI has been calculated for more than 1100 samples along the Swedish West Coast. It is considered as more 'objective' than the precedents. It has been applied successfully in the northern European seas and could be a very useful tool within the EU Water Framework Directive.

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