Pelagic coelenterates in the waters of the western part of the Egyptian Mediterranean Coast during summer and winter

摘要

During August 2000 and February 2001 two cruises were carried out along the Egyptian Mediterranean Coast on the Egyptian r/v "El-Yarmouk". The samples collected were used to study the ecology and distribution of hydromedusae and siphonophores during summer and winter. The density of hydromedusae was high in the inshore waters during summer (av. 71 org × 100 m-3), decreasing to 28 organisms per 100 m3 in the oceanic waters; in winter they were more abundant in the middle and offshore zones. A total of 9 hydromedusae species were recorded during the present study, 8 of them in summer. The most common of these were Aglaura emistoma, Olindias singularis, Liriope tetraphylla and Geryonia proboscidalis. Only 4 species were recorded during winter, including Cunina octonaria, which was not recorded during the summer. The nine species recorded in the present study are circumtropical. The siphonophore density was high in summer. In winter, the average standing crop of siphonophores fell to about 30% of that recorded in summer. 11 siphonophore species were recorded, 10 of them in summer; Cucullus campanula and Eudoxoides spiralis were the most common. Only 6 species were recorded in winter. These 11 species are widely distributed - they have been recorded from the Atlantic, Indian and Pacific Oceans. Strong seasonality is thus a striking feature of Egyptian Mediterranean waters. Temperature is the most variable factor affecting the planktonic community, fluctuating between 26.5 and 27°C in summer and between 16.3 and 17.5°C in winter. The western part of the Egyptian coast, the area under study in this work, is poorly diversified in comparison with the eastern part.