Short term variations of zoo plankton community in the West Naubaria Canal, Alexandria, Egypt
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The variations of zooplankton structure and abundance were studied at short time intervals in the northern part of the West Naubaria Canal, near the sea side, based on weekly sampling from May 2002 to May 2003 .The community represented high species richness (120 species), and relatively low population density ( annual average 31340 organisms/m.3). Freshwater forms were the major representatives (68 species) of the community, including the sea side station. However, several marine species were reported inside the canal at a long distance from the sea. The community structure showed wide weekly variations (4-29 species), while between stations the differences were small. Relative to salinity in the canal, diversity index sustained the highest value (annual average 1.8) at the sea side station (St. 1) with surface salinity 11.1 PSU compared to the values reported at the other stations (annual averages 1.5-1.7) with average salinity was 8.7, 7.6 and 6 PSU at stations 2, 3 & 4 respectively. The diversity index experienced also clear temporal variations at all stations, parallel to those of standing crop and number of species. The zooplankton abundance showed wide changes on both scales of time and space, with an annual average of 34.4, 17.1, 33.2 and 40.6 x 103 organisms /m3at station 1-1V respectively, and weekly values varying from a minimum of 150 organisms /m3 to a maximum of 797.7 x 103 organisms /m3. Despite of salinity differences, copepods, mainly their nauplii larvae were the absolute predominant component at all stations representing a very stable fraction of zooplankton forming 66.1%-77.9%, while different patterns of co-dominance were observed at different stations relative to salinity variations.