The assessment of ecological quality is a hot issue in marine research. The approaches to assess the ecological quality of a given water body, are based either on the physical, chemical (priority substances including), or biological elements of the system. The biological elements proposed for this topic have been manifold, ranging from molecular to ecosystem level. However, the most fundamental implement seems to be the benthic fauna as (1) it shows small natural variability compared to pelagic one, (2) it is well responding to organic pollution, and (3) it is rather localized, which means that most species are either sessile or discretely motile, thus not performing large-scale migrations. So they do reflect the integrated conditions over a time period. The concept of ecological indicators has been developed for this assessment; meaning any organism whose presence and/or dominance in a particular area can reveal the prevailed environmental conditions, characterizing the degree of community change or pollution effect. It is widely accepted that when more than a few species are taken into consideration, the indices' validity increases. Therefore, instead of working with a specific taxon, it is better to consider the ratio of taxonomic or functional units (i.e., species, genus, families, trophic guilds, reproductive mode, life strategies, ecological requirements); this approach has led to the invention of a wide number of ecological indicators which have been tested in several cases of pollution with varying degrees of success.
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