Ecological indices as a tool for assessing pollution in El-Dekhaila Harbour (Alexandria, Egypt)

Statistical analyses of data concerning the phytoplankton standing crop and biomass were applied as a tool for assessing pollution in El-Dekhaila Harbour. Univariate and multivariate analysis showed a succession of three clusters associated with salinity and temperature variations. The first and third clusters comprised mainly diatoms and dinoflagellates. The second cluster, richer in species, was dominated by brackish water cyanophytes, chlorophytes and euglenophytes. The diversity index ranged from 0.08 to 2.41. A high diversity was associated with high evenness, reflecting the multidominance pattern of cluster (2). On the other hand, multiple correlations between salinity and standing crop, richness and evenness, were negative and significant, but positive with the diversity index. The ABC curve showed that the k-dominance curve for numerical abundance extends above that for the biomass when clusters 1an d 3 are dominant. Both curves coincide more or less for another segment of the curve but when cluster 2 becomes dominant the numerical abundance curve runs below that of the biomass. Such a pattern may indicate unpolluted or moderate to heavily polluted conditions in El-Dekhaila Harbour. The present study reveals that the combination of univariate and multivariate analysis with the ABC curve provides a promising tool for the characterization of phytoplankton dynamics under stress conditions. On the other hand, the phytoplankton community in El-Dekhaila Harbour is stressed not by the inflow of brackish water but rather by the inflow of sea water. This is indicated by the higher diversity and evenness, and by the ABC curve during the dominance of cluster (2).