Responses of Zooplankton to Long-Term Environmental Changes in the Egyptian Coastal Lakes

Abstract

The Egyptian Mediterranean coast has four brackish lakes (Northern delta lakes) and a hypersaline one. These lakes are, from east to west, Bardawil, Manzala, Burullus, Edku, and Mariout. All except Lake Mariout are directly connected to the sea. These lakes represent highly dynamic aquatic systems that have been undergoing continuous and pronounced changes through the late Holocene to the present time. Changing natural conditions are influencing the diversity of biological community and its function. Zooplankton is considered as a sensitive tool to any changes in water environment. Therefore, the impacts of any natural changes can be identified through changes in species composition, quantity, and size. Nowadays, despite their physical separation, the delta lagoons appear to have similar zooplankton populations. Rotifers comprise at least 80% and often higher than 90% of the total population in the lakes. In comparison with deltaic lakes, the non-deltaic one (Bardawil Lake) shows a different zooplankton assemblage which composed of marine species copepod seems the leading group followed by protista and pteropoda. The zooplankton assemblage shows no much change until the 1950s. By the 1970s, Daphnia had become a rarity and was actually not recorded from the lakes. The 1960s–1970s were marked by three new arrivals in the zooplankton, all of the Mediterranean origin: Arctodiaptomus salinus, Acanthocyclops trajani, and Diaphanosoma mongolianum. To accelerate the restoration of the delta lakes to better conditions for saving them as grounds for fisheries and places for recreations, the quality of the sewage and industrial wastes dumping directly into them or indirectly via agricultural drains must be treated.