Port 3 W1 S1 W2 S2 Port 5
Figure 2 The performance of P/A index on organically polluted hard-substratum communities (Thermaikos Gulf, North Aegean Sea), where S = summer, W = winter, and 1-3 the successive years of the study.
calculations to be used by nonexperts; (2) be sensitive to any pollution event, as well as to detect gradients of disturbance; (3) assess different types of contamination; (4) incorporate seasonal variations; and (5) be applicable to various ecosystems and geographical areas.
P/A index follows some of the above desirable features. It is based on a very simple calculation formula and it appears sensitive to the assessment of various contaminants, detecting alterations from oil spill and waste material disposal, and also integrates seasonal oscillations of the fauna. However, a question arises on its discriminative power, robustness, and wide-scale applicability. Obviously the applicability of P/A index is completely improper on hard bottoms, while it is dubious considering assorted sediments, in which the structure of polychaete and amphipode fauna is highly variable and driven mainly by a complex ofecological factors. Also, its performance is bad when the samples are poor, or when polychaetes are not the dominant taxonomic group. Due to these drawbacks P/A index has a rather limited applicability and approaches of ecological quality assessment should rank the entire benthic fauna with respect to either its sensibility/tolerance to pollution (e.g., biotic indices such as AMBI or BENTIX), or a specific taxonomic group (e.g., the polychaete index of Bellan, the amphipod index of Bellan-Santini, or the peracarid index of Chintiroglou). Still, the entirety of ecological indicators also suffer from some of the above weaknesses, and it seems that no approach is a panacea offering a solution in all cases of environmental deterioration, demonstrating the necessity for intense scientific research on this topic.
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