Seasonal and spatial distribution of Brachionus (Pallas, 1966; Eurotatoria: Monogonanta: Brachionidae), a bioindicator of eutrophication in lake El-Manzalah, Egypt

Rotifers, especially Brachionus sp., are the major component of zooplankton in Egyptian eutrophic lakes. Thesespecies play an important role as bioindicator in these aquatic environments. In present study, twenty-fourzooplankton samples were collected and investigated along six stations of southeastern sector of the lake fromAugust 2009 to May 2010. Brachionus sp. were the most abundant species constituting 74.8 % of the total rotifersand 59.87 % of the total zooplankton. It was represented by 7 species which are; Brachionus angularis, B.budapestinensis, B. calyciflorus, B. caudatus, B. plicatilis, B. urceolaris and B. quadridentatus. The highestabundance of Brachionus sp. was recorded at Ibn Salam Station (4227493 Org./m3) during summer due to the effectof water discharge rich in nutrients through 3 main drains in this area while the lowest abundance was recorded at El-Qaboti Station (333 Org./m3) during winter. Brachionus angularis and B. calyciflorus formed collectively (92.16 % ofthe total Brachionus sp.). The presence of these species of Brachionus in high composition indicates eutrophicationof Lake El-Manzalah.