Zooplankton in Lake Sevan during the period of high water level and low fish density

Abstract

It is shown that, upon the flooding of ephemeral waterbodies in the coastal region and the forma tion of new warmer sites of the shoals due to the rising water level in Lake Sevan in 2011, species typical for temporary waterbodies and various shoals have been recorded in the zooplankton. Among them, Daphnia (Ctenodaphnia) magna Straus reached mass development, which was favored by the minimal control from "the top" and favorable trophic conditions. Owing to the abovementioned factors, the total lake zooplankton biomass and water transparency increased. The uneven distribution of D. (C.) magna was determined by the density of fish that prefer it as food.

Short Communication: Mollusks biodiversity of Lake Sevan, Armenia

“…So, there have been significant changes in species structure and number of fish population. The species richness of zooplankton and the appearance of two new for the lake species of Cladocera family among the dominants were observed (Krylov et al 2013). However, by 2011, the stocks of fish in the pelagic zone of the lake dropped to its lowest values ever recorded (Krylov et al 2013).…”

“…From 1978, when the National park Sevan and channels Arpa-Sevan, Vorotan-Arpa were built, water level rose, and it had increased by 360.5 cm by 2011 (Krylov et al 2013).…”

“…Unfortunately, insufficient hydrobiological shooting during the vegetation period does not allow the authors to be certain about the current state of Lake Sevan. Available hydrochemical data of the lake water and the changing parameters of aquatic organisms communities indicate the ongoing process of eutrophication (Krylov et al 2013;Krylov et al 2015). The trophic status of the lake is expected to vary in the future, and it will acquire additional features of the eutrophication process associated with fouling, benthic fauna, macrophytes overgrowing.…”

Spatial distribution of zooplankton in the Kolsaiskie mountain lakes (Kungey Ala Tau, south-east Kazakhstan) and its connection with environment factors

“…Межгодовое увеличение разнообразия по обще-му числу видов и количественных показателей зоопланктона в озерах Нижний, Средний и Верхний Кольсай также могут служить признаками эвтрофирования. Аналогичные изменения структуры отмечены для зоопланктона горных озер Севан [40] и Сон-Куль [6][7][8]. В отличие от трех нижних озер, в Сары-Булаке межгодовой линейный рост биомассы зоопланктона сопровождался укрупнением входящих в сообщество видов и соответствующими изменениями значений W-статистики Кларка, Δ-Шеннона-Уивера и средней индивидуальной массы особи.…”

“…При снижении уровня повышается температура придонного слоя воды и усиливается поступление биогенных веществ в воду [26]. Как следствие, признаки эвтрофирования водных экосистем более отчетливо проявляются в периоды низкого уровня воды [34,40,50], что наблюдалось и в Кольсайских озерах.…”