Indices Based on Ecological Strategies

Some indices aim at assessing environmental stress effects taking into account the ecological strategies followed by different organisms, although several authors rejected them due to their dependence on parameters such as depth and sediment particle size, as well as because of

Table 4 Upper limits of BCR for hazardous substances in blue mussels (OSPAR/MON, 1998)

Substance

Upper limit of BCR value (ngg 1 dry weight)

Cadmium

550

Mercury

50

Lead

959

Zinc

150000

their unpredictable pattern of variation depending on the type of pollution.

Nematodes/copepods index. This index, introduced by D. G. Raffaelli and C. F. Mason in 1981, is based on the ratio between the abundances of nematodes and copepodes:

Nematodes abundance Copepods abundance

The values of such ratio can increase or decrease in response to higher or lower organic pollution, which expresses a different response of those groups to the input of organic matter into the system. Values over 100 express high organic pollution.

The application of this index should be limited to intertidal areas because in infralittoral zones values can be naturally very high. This fact is explained by the the absence of copepods at more than a few meters deep, most probably due to a change in the optimal interstitial habitat for that taxonomic group.

Meiobenthic pollution index (MPI). This index was introduced by G. V. Losovskaya in 1983, with the following equation:

H, P, and N are the numbers (individuals m~2) of Harpacticoida, Polychaeta, and Nematoda, respectively, in a given benthic sample.

Increasing impacts induce the replacement of harpac-ticoides and polychaetes by nematodes, and such a shift can be traced through changes in the values of the index.

Mollusks mortality index (MM/). This index was elaborated by A. N. Petrov in 1990 for marine environment:

Weight of shells of recently dead mollusks Total weight of living individuals and the shells of mollusks of the same species

High values of the index are indicative of disturbances.

Polychaetes/amphipods ratio. This index, introduced by J. L. Gomez-Gesteira and J. C. Dauvin in 2000, follows a similar principle to the nematodes/copepods ratio, but addresses macrofauna and accounts for polychaetes and amphipods. Originally, it aimed at evaluating the effects of crude pollution:

Polychaetes abundance Amphipods abundance

/< 1: nonpolluted and /> 1: polluted. This index is treated extensively in Polychaetes/Amphipode Index.

/nfaunal trophic index (/T/). Macrozoobenthic species can be divided in: (1) suspension feeders, which collect detrital materials in overlying water; (2) interface feeders, which collect detrital small size materials (usually <50 mm in diameter) that settle on the surface of the sediment; (3) surface deposit feeders, which collect larger particles within the upper 2 cm sediments layer; (4) subsurface deposit feeders, which generally collect particles that are buried deeper than 2 cm, often in the presence of hydrogen sulfide. The value of ITI, elaborated by Word in 1980, is given by

where n1, n2, n3, and n4 are the number of individuals sampled in each of the above mentioned groups.

ITI values near 100 mean that suspension feeders are dominant and that the environment is not disturbed. Values near zero mean dominance of subsurface feeders, and a strongly disturbed environment. Index values less than 60 on the scale are highly correlated to BOD and TOC or volatile solids in the upper 2 cm of the sediment, while values above 60 are less correlated to accumulation of organic materials in the sediment.

Feeding structure index (FSF). This index, introduced by N. Y. Milovidova and S. V. Alyomov in 1992, was formulated for marine environment:

No. of species of filter - feeders No. of species of deposit - feeders + predators

This index is based on the fact that in less eutrophic areas, the number of filter-feeders species is 6-8 times greater than in highly eutrophic areas. Its application is nevertheless complicated because of difficulties in assigning correctly a trophic category to each individual: Feldman index.

^ No. of Rhodophyceae species No. of Phaeophyceae species

M. Cormaci and G. Furnari in 1991 detected values over 8 for this index in polluted areas, while normal values, in a well-balanced community, should vary between 2.5 and 4.5. Nevertheless, several observations illustrate that knowledge about the behavior of this index does not seem to be enough to consider it, by itself alone, a good pollution indicator.

Belsher index. This index, elaborated in 1982 by T. Belsher, holds on the higher or lower sensitivity of Phaeophyceae and Rhodophyceae to disturbances and is based on the qualitative and quantitative dominance of each taxonomic group:

... % species of a taxonomic group

Population species

% cover area by a group

Total cover area

The ratio between qualitative and quantitative dominance is called tension It has been observed that alongside decreasing pollution gradients, certain groups of algae increase or decrease their tension, establishing the following relation, which was considered a pollution index:

EVj where i = groups with decreasing tension and j = groups with increasing tension.

The values of the pollution index are high in polluted areas and nearly null in normal zones, but boundary conditions between different states of disturbance are not evident, meaning that the knowledge about this index behavior does not seem to be enough to consider it, by itself alone, a good pollution indicator. It has only been applied in rocky substrate areas.

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