Credit: Olfat Anwar (Egypt)
The photos show the sampling of plankton in Lake Nasser using plankton nets equipped with flow meters (shown in the middle). The flow-meter measures the quantity of water filtered through the plankton net and hence enables relating the results to units of water. There are two types of plankton nets based on their mesh size; the 0.1-mm-mesh net is used for all plankton types (phyto and zooplankton), while the 0.3-mm mesh net targets mainly zooplankton.
The method used in this analysis adopts the vertical haul in which the plankton net is lowered from a stationary ship in the water till reaching the desired depth then immediately pulled upward. The flow-meter measures the quantity of water filtered through the net. Afterwards, the collected plankton is processed (e.g. preserved, enumerated) as planned in the analysis (e.g. qualitative, quantitative, wet weight, dry weight) and relates the results to a unit of water. In Lake Nasser, water is analysis at depths that range from surface water till 20-meter depth at 5-meter intervals.