Eutrophication stress on phytoplankton community in the Western Harbour of Alexandria, Egypt

The dynamics of phytoplankton community was studied monthly for a complete cycle in an eutrophic bay (the Western Harbour of Alexandria) and the results were compared with previous records to identify the modifications occurring in the community within the past decade. The study indicates serious qualitative and quantitative changes in the phytoplankton community. The species number increased from 68 to 107, with approximately complete replacement of the dominant species, the leader of which were the dinoflagellates Alexandrium minutum Halim and Prorocentrum triestinum J. Schiller and the diatom Skeletonema cf. costatum (Grev.) Cleve. The former species was known as predominant for about the past four decades in the Eastern Harbour of Alexandria, but it disappeared from that harbour in the recent records. During the present study, dinoflagellates became the more effective contributor to the standing crop (57%) than diatoms (41%), coincided with shifting of the blooming times towards the warmer period. An intimate association and significant correlation were reported between the dinoflagellate A. minutum and each of Prorocentrum micans Ehrenb and P. triestinum and the euglenophycean Euglena acus Ehrenb. Salinity and temperature were the controlling factors of dinoflagellate growth, while SiO₄ and PO₄ were promoting for the whole phytoplankton.