On an ideal level, it is very obvious that the bioevaluation of communities and the predictive diagnosis of their spatiotemporal evolution should rely on a thorough knowledge of their structure and their functioning, and even on their modeling. It is necessary to take great care in addressing the problem of their modeling. Its solution, especially in the marine benthic environment, appears not to be based on a short-term evolution. It is also clear that the simple use of traditional indices of diversity or similarity demands complete and complex knowledge, which leaves little chance that they could be used immediately in the sphere of bioevaluation. In the more restricted field of monitoring the evolution, positive or negative, of assemblages affected by man-made disturbances, the use of biological indicators and biological (pollution) indices seems to be an effective alternative. 'Objective' or 'subjective', the procedures for selection of sensitive species able to indicate changes in communities due to perturbation are not only interesting but also promising. The problem is again a matter of methodological adequacy of biological indices with the level of complexity and structure of communities observed in a given place.
It appears to be difficult, even uncertain, to obtain a unique index (or global index); such an index should answer different needs on different scales of time and space. Nevertheless, indices could be applied on large scales to be representatives: that is the challenge!
On the other hand, we have to keep in mind that we do not anymore be in face of only polluted or disturbed environment, but their recovery, often linked to man-made improvements, is important. It is time now to search new panels of indicators and indices to put in evidence these improvements, that is 'quality indices'. It is always from knowledge on the structure and functioning of assemblages and ecosystems that the tools must be built consistent with the desired predictive diagnostic of the 'quality'. We can expect these 'quality indices' to be specifically developed in the near future.
Anyway, it is not always possible to wait for the research results because the demands for the procedures of prioritization are more and more pressing. Empiricism cannot be avoided, however discomforting it may be. It is in the corpus of knowledge that we already have to choose to obtain a 'practical savoir-faire'. It must be faithful: that way it will be reliable.
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