Species composition and spatial structure of the zooplankton community in Lake Inorki (Mordovia State Nature Reserve, Russia)
Authors: Stojko T.G., Senkevich V.A.
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The present study is devoted to the study of species diversity and spatial distribution of the structural parameters of zooplankton community in the lake-oxbow Inorki in 2014 and 2016. The lake is in the middle right-bank floodplain of the River Moksha. The area of the lake is 0.209 km2, the maximum length is about 3.7 km, the average width is about 95 m and the depth is 3.5–5.5 m. The riparian part of the lake is steep. And at a distance of 1–2 m from the shore the depths reach 1.5 m in most places. Zooplankton samples were taken on three stems (one in the centre, at a depth of >200 cm, and each shore, at a depth of 80 cm) in three sections from the boats early July 2014 (water temperature: 24–27ºC) and 2016 (water temperature: 21.5–22ºC) and treated by conventional methods. By compiling the list of zooplankton species, in Lake Inorki we have obtained the data of the three samples in June 2009 (54.7265º N; 43.1523º Е) and five samples early July 2013. We have detected 93 species and forms of zooplankton. There are rotifer species of the Middle Volga region: Asplanchnopus multiceps, Euchlanis proxima, Squatinella mutica, S. rostrum, S. tridentatа, Trichocerca weberi which prefer the overgrown and waterlogged water bodies. 11 species in Lake Inorki have been registered in all years of study: Asplanchna priodonta, Conochilus hippocrepis, Keratella cochlearis, Lecane closterocerca, Mytilina ventralis, Synchaeta pectinata, Testudinella patina, Chydorus sphaericus, Graptoleberis testudinaria, Sida crystallina, Mesocyclops leuckarti. The average abundance of zooplankton is significantly higher in the pelagic part of the lake than in its coastal zone (t = 8.82–11.38, at p < 0.05). The taxonomic structure of zooplankton community showed differences. So, in 2014 rotifers dominated, while in 2016 the abundance of nauplial stages copepod was the highest. Perhaps, at the time of sampling in 2016, the zooplankton community was at the earlier stage of seasonal dynamics due to low water temperature. This year there was a smaller number of dominant species and a high spatial homogeneity. The ratio of ecological zooplankton groups was different through the years and parts of sampling. In 2014 verticators mainly dominated. Moreover, their percentage was the highest (78%) in the open part of the lake. In 2016 apart from filter-feeders, the zooplankton community was presented by a high proportion of grabbers, nauplii and Copepods larvae: their proportions were 65% and 50% near the lake shores and 44% in the centre of the lake. The state of Lake Inorki has been estimated as mesotrophic according to the Shannon index and the trophy coefficient.