Abstract
The aim of this study was to determine factors affecting the vertical distribution of Eurytemora lacustris in mesotrophic lakes (Wigry, Hańcza, Szurpiły; north-eastern Poland) during the summer stagnation. Eurytemora lacustris was found in all of the studied lakes, with the highest abundance (8 ind. L−1) in Lake Wigry. In Lake Szurpiły, E. lacustris has never been recorded before. The results of this study revealed that E. lacustris was most numerous in thermocline zones, suggesting that this species could temporarily tolerate warmer water and lower oxygen concentrations due to better food resources. During the study, it was found that a large part of the E. lacustris population had epibiont ciliates, in contrast to other species of zooplankton that did not have any epibionts. The improvement in the water quality of many deep lakes could lead to an increase in the abundance of E. lacustris. However, epibiont ciliates may be a threat for this species and may play a substantial role in determining the production, distribution, and community dynamics of E. lacustris.
Highlights
Eurytemora lacustris (Poppe, 1887) is considered a ‘classical’ glacial relict species in central Europe (Maier et al 2011), while the inclusion of this species in the relict element in Norway and Sweden has been discussed (Kinsten 2012; Spikkeland et al 2016)
Our study revealed that a large part of the E. lacustris population had epibiont ciliates, in contrast to other species of zooplankton
The improvement in water quality has led to an increase in the population of E. lacustris in deep lakes; epibiont ciliates could be a threat for E. lacustris populations and may play a substantial role in determining community production and dynamics
Summary
Eurytemora lacustris (Poppe, 1887) is considered a ‘classical’ glacial relict species in central Europe (Maier et al 2011), while the inclusion of this species in the relict element in Norway and Sweden has been discussed (Kinsten 2012; Spikkeland et al 2016). From the zoogeographical point of view, E. lacustris is a typical so-called Baltic species, with a distribution related to the Ancylus stage of the post-glacial Baltic Sea development (Spikkeland et al 2016). According to Thienemann (1950), E. lacustris is a cold-adapted calanoid copepod which spread over parts of Europe by glacier lakes during the last ice age, about 8500 years ago. During the post-glacial period, when the temperatures gradually increased, E. lacustris was able to survive by retreating to the cold water layers of thermally This species is a very good indicator of the low trophic level and good ecological status of lakes (Karabin 1985; Ejsmont-Karabin and Karabin 2013; Ochocka and Pasztaleniec 2016)
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