Seasonal changes and abundance of rotifers in a shallow Manzalah lake (Egypt)

Manzalah lake is a eutrophic coastal lake that has been flooded by excessive agriculture drainage over the last 30 years, changing its ecological status. Fifty-two taxa of rotifers were identified, of these Brachionus angularis, Brachionus plicatilis, Keratella quadrata, Polyarthra vulgaris and Synchaeta oblonga were abundant. The maximum population density (lake average 490 individuals L−1) occurred in winter, while the taxa were low in abundance during summer and autumn. The participation of rotifers has increased from 16 species, forming 24% of the total zooplankton in 1971-1973 to 52 species, accounting for 85.1% now. This was concurrent with the progressive dulcification and eutrophication of the lake water.