Marine benthic communities; in particular the soft bottom polychaetes along the western coast of Alexandria, were studied as part of a monitoring program on the effects of human activities on the ecosystem to determine whether discharges from the wastewater outfalls are affecting the surrounding benthos or nat. These communities
are used as indicators of sediment and water quality because they can consume or adsorb the pollutants via feeding processes. Data analyses of benthic communities are commonly used to estimate the changes of complexity of the community structure in the stressed area due to one or more of environmental factors. Soft bottom polychaetes in this area were studied using multivariate and biotic indices, measuring abundance and community composition. Possible significant correlations were determined using multi regression analysis with physical, chemical and biological
structure. Twenty six polychaete species belonging to 16 families were identified. The benthic polychaete communities in the study area were dominated by two sedentary forms (Capitellidae, Spionidae) and two errantia forms (Nereidae, Syllidae) besides to unidentified Oligochaeta species. These communities were more dominant in the area
near outfalls of El Amom drain, El Dekhelah, Nobaria drain and SUMED area, where their frequencies varied among sites and within sites over the study period. Shannon's index (H') varied spatially from 0.49 to 1.76, Margalef richness index (d) from 0.17 to 1.58, and evenness index (J) from 0.44 to 0.79, indicating poor polychaete diversity.
High diversity may be attributed to the presence of oppertunitistic species, which are tolerant to high organic matter and chemical residues. The relative frequency of abundant polychaetes can be ranked as follows: Capitella (15.4%) > Oligochaeta (14.9%) > Polydora (14.4%) > Prionospio (11%) > Nereis (10.6%) > Syllis (5.4%).
Sedentary polychaetes (Capitellida capitata, Polydora caeca, Prionospio cirrifera) and an errant form (Nereis irrorata) were regularly distributed within stations but their abundance varied between stations. The highest density of species and
specimens were recorded at stations 2, 4, 5, 7, 8, and 11, where the tendency of abundance increased from May to July reaching 1092 to 1385 ind./m2. The increase in polychaete abundance observed in outfall area could be due to the effect of trophic level.