Ecosystem changes in the Egyptian saline Lake Qarun during the XX–XXI centuries (short review)

Abstract

Since beginning of the 20th century the salinity growth in Lake Qarun (Egypt) accelerated. Changes in the specific structure of plankton and benthos have been observed. Three stages of biotic changes may be separated. The salinity change determined biodiversity transformation only until 1928. Due to natural causes new species invasions – marginal marine (Cerastoderma glaucum, etc.) and halotolerant lacustrine (Arctodiaptomus salinus, Moina salina, etc.) – occurred, reducing the diversity and abundance of freshwater forms. Because of the growth of salinity the certain species of fish began to disappear in the lake. Catch of fish has fallen sharply, affecting the standard of living of the local population on the shores of the lake. To improve the situation, in 1928, people started to introduce the young marine fishes and crustaceans. Some species of introduced animals began to breed successfully, but not all, so the fry of some species of fish are transported annually from the sea into the lake. The second stage of the biotic transformation in the lake started, when the mass directed and accidental marine aquatic organism introduction by people was the main reason. The flow of marine species increased, halotolerant lacustrine species have disappeared, and the maritime community has formed. In 1950–1970s, intensive eutrophication began; it and alien species anthropogenic introduction have become the driving forces of the ecosystem changes. In the next decades, the main causes of changes in community structure will be eutrophication, pollution and aliens, especially jellyfish Mnemiopsis leidyi, invaded the lake in 2014.