الفهرس 
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Abstract
Each species on our planet plays a role in the healthy functioning of natural ecosystems, on which humans depend, Gelatinous zooplanktons are a conspicuous, but relatively little studied component of marine ecosystems, in recent years its importance in pelagic food webs has gained increased awareness, they are essential components of the marine food web, relaying primary production from microbial algae to fish and seabirds. Marine systems are based on microscopic life and, thus, are generally undervalued. Most conservation purposes are first biased in favor of terrestrial systems and, when the sea is considered, in favor of big, charismatic species, usually vertebrates and higher plants (with the sole exception of corals and some mollusks). The Hydrozoa are no exception and, thus, tend to be considered as “negligible” if compared to groups that are more “visible”. This attitude is based on a naive way of conceiving ecology and is simply wrong (Boero et al., 2001). Small hydromedusae feed omnivorously on micro planktonic prey. The trophic roles of small hydromedusae in different systems are not understood and more studies are needed. However, based on their often high abundances and the cosmopolitan nature, if small hydromedusae are primarily omnivores, they need to be considered when estimating the impact of zooplankton on primary production and, more generally, Protista community dynamics.
The main aim of the present work was to provide a classification informations, biogeographic distribution, a quantitative and qualitative study of different species of planktonic cnidarians (hydromedusae and scyphomedusae), and ctenophores in the Egyptian Red Sea, at Hurghada coast during August 2014 to July 2015 lie between latitudes 27°14.362ˊ N and 27° 8.371ˊN, and longitudes 33 °51.235ˊE and 33 °51.46ˊE. A total of 3 sectors. Each sector was further divided into two sites perpendicular to coastline. Samples were collected using simple plankton nets with different mesh size monthly, and were fixed in 4% formaldehyde. The samples were examined using a stereomicroscope, and then calculating the densities. Identification and classification of recorded species have been based on the morphological and anatomical characteristics of some species according to the important identification references, among (Mayer, 1910; Boltovskoy et al., 1999; Bouillon et al., 2004; Bouillon et al., 2006)
The recorded number of gelatinous zooplankton during the present study included 24 species, constituting about 22% of all recorded zooplankton community in the study area. Hydromedusae were the dominant component among gelatinous zooplankton, consisting on the average about 74.29% of the total gelatinous zooplankton (18 species), followed by scyphomedusae 15.56% (3 species). Of the all 21 species, belong to Phylum Cnidaria, twelve were the first record in the Egyptian Red Sea. Of them, 10 species (C. octonaria, C. noliformis, E. gegenbaueri, E. mira, E. bigelowi, L. fijiana, L. clausa, O. ocellata, P. porpita and S. bedoti) belong to Superclass Hydrozoa, and only one species (P. punctata) belong to Superclass Scyphozoa. Only three species belong to the Phylum Ctenophore were recorded, two species (M. leidyi and P. pileus) recorded for the first time in the Egyptian Red Sea during the present study.
Temporal variations in mean abundance of recorded gelatinous zooplankton species showed that, of all recorded gelatinous zooplankton three species only were dominated the community. The Siphonophores D. chamissonis (28 %) and the hydromedusa A. hemistoma (22 %) of the total catch densities. Other abundant species such as P. pileus (12 %) which belongs to phylum Ctenophora has not been previously reported in Red Sea Egyptian water. Other scyphomedusae A. aurita recorded with highest peak in April 2015 (av. 41.8 ind. / 103 m3).
The analysis of the spatial distribution of gelatinous zooplankton species showed that the three gelatinous species (A. hemistoma, A. aurita and D. chamissonis) were observed at all sectors of study area. The current study indicated that, the highest abundance of recorded gelatinous species was recorded at offshore sites (especially site 4) than inshore sites. This May be according to their depths range from 50 - 300m, while the diversity was high at inshore and offshore sites due to the 33% of recorded species considered as a costal species. This coastal community formed by L. tetraphyla, C. contorta, E. mira, E. gegenbaueri, E. quadrivalvis, Obelia sp., L. clausa and P. punctata.
Despite the ecological importance of the gelatinous marine zooplankton in the marine food web so monitoring program is needed to record the recent gelatinous species in the Egyptian waters and follow up the distribution and abundance of those previously recorded as alien species in the Egyptian Mediterranean and Red Sea waters to assess their impacts on the native biodiversity of both seas. The monitoring program must be accompanied with studies on the feeding habits of these gelatinous species to detect the role of these species in the food web and to understanding how gelatinous zooplankton populations will behave because these are the most predator of fish larva and fish egg. In this way, a more advanced technique should be developed for identification such as DNA analysis to reach the species level.