Zooplankton Dynamics and Ecology of an Eutrophic Area, Egypt PDF

Keywords

zooplankton, phytoplankton, ecology, Egypt

Abstract

The qualitative and quantitative dynamics of a zooplankton community were studied monthly over a year in relation to the variable environmental conditions in Dekhaila Harbour, a coastal eutrophic area. The temporal changes of water temperature were similar to those previously known along the southeastern Mediterranean coast (15 - 29°C). Dissolved oxygen varied between a low level of 1.7 ml/L and well oxygenated conditions (8.3 ml/L). Surface salinity suffered from marked seasonal and regional variations, falling between 17.34% and 39.18% over the year. The low transparency was one of the characteristic features of the harbour water, where Secchi depth maintained low values (45-270 cm). The phytoplankton chlorophyll a showed an abnormally wide range of variations from a significantly low value of 1.63 mg/m^3 to an abnormally high one (1323 mg/m^3). The species composition and density of zooplankton were clearly affected by the ecological variations. The annual average count (22640 organisms/m^3) demonstrated a relatively low standing crop, fluctuating all the year round between 781 and 236644 organisms/m^3. The zooplankton community showed a group structure more or less different from those usually known in the coastal Egyptian Mediterranean waters. The protozoans appeared as the major constituent, forming 66.1% of the total catch, and copepods came in second (26.5%). The bulk of zooplankton density was attributed to a few species, including the tintinnids Favella serrata, Tintinnopsis nana, T. Lata, T. compressa and Eutintinnus lusus-undae and the copepod Oithona nana, which all together formed 62% of total count. Several freshwater holoplanktonic forms were recorded in the area, contributing 2.7% to the total crop, and reflecting the impact of the discharged wastewater. The temporary planktonic assemblages played a small role in the study area, averaging annually 5.2%, with the dominance of the larval stages of polychaetes and cirripedes. The index of biotal despersity, diversity index and species richness exhibited pronounced temporal and spatial variations as a reflection of environmental changes.