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2 Oceanologia

2 2003

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

Ismael A. A., Dorgham M. M.

Oceanologia

2003

No. 45 (1)

121-131

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 1 and 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).

Alexandrium minutum cysts in sediment cores from the Eastern Harbour of Alexandria, Egypt

Ismael A. A., Khadr A. M.

Oceanologia

2003

No. 45 (4)

721-731

Alexandrium minutum cysts were studied in sediment cores from its type locality, the Eastern Harbour of Alexandria, following the disappearance of the species from the plankton since 1994. Three cores were sampled in the summer of 1999 along the north-south axis of the harbour. The sediments were subjected to grain size analysis and their organic carbon content was determined. The sediments consisted of medium, coarse and very coarse sand. Grain size and organic carbon content were negatively and significantly correlated in core 1 but followed a parallel trend in cores 2 and 3. Seven dinoflagellate cysts, representing 6 genera were identified from the cores. Their relative abundance showed a remarkable difference. A. minutum cysts contributed a maximum of 17.4% to the total cysts. The distribution profile of A. minutum cysts in the cores reflects the bloom duration but not its productivity. The cyst distribution in the cores is the resultant of two opposite processes, the sedimentation rate and the continuous erosion of the bottom sediments, which is not related to sediment texture.