Trophic state (TSISD) and mixing type significantly influence pelagic zooplankton biodiversity in temperate lakes (NW Poland)

Background Lake depth and the consequent mixing regime and thermal structure have profound effects on ecosystem functioning, because depth strongly affects the availability of nutrients, light, and oxygen. All these conditions influence patterns of zooplankton diversity. Zooplankton are a key component of the aquatic environment and are essential to maintaining natural processes in freshwater ecosystems. However, zooplankton biodiversity can be different regard to depth, mixing type and trophic state. Therefore, the aim of this study was to examine how depth and mixing regime affect zooplankton diversity in lakes. We also investigated the vertical distribution of diversity across a trophic gradient of lakes. Methods A total of 329 zooplankton samples from 79 temperate lakes (36 polymictic and 43 dimictic) were collected. The biodiversity of zooplankton was calculated using species richness (SR) and the Shannon index (SI). An index based on Secchi disc visibility was used to determine the trophic state index (TSISD) of lakes. The one-way ANOVA with Duncan’s post hoc test were used to determine differences in zooplankton biodiversity between mictic lake types and thermal layers. To find the best predictors for zooplankton biodiversity a multiple stepwise regression was used. The rarefaction method was used to evaluate the impact of mixing types, thermal layers, and the TSISDon zooplankton biodiversity indices. A Sørensen similarity analysis and nonmetric multidimensional scaling (NMDS) were performed to describe the similarity patterns in species composition among lakes. Results We identified a total of 151 taxa from 36 polymictic and 43 dimictic lakes. Lake depth and the TSISD were significantly correlated with the biodiversity of lake zooplankton. The results of ANOVA and Duncan tests show that mictic type and thermal zones had a significant effect on zooplankton biodiversity. The rarefaction curve showed significant differences in zooplankton biodiversity, which was greater in lakes with lower trophic state. Ordination by NMDS showed clustering of different mictic types, thermal layers, and composition changes throughout the TSISDprofile. Moreover, we determined that polymictic lakes are more heterogeneous than dimictic lakes in regard to zooplankton similarities. Discussion Both mictic lake types were characterized by varying levels of zooplankton biodiversity, which is shaped by the communities’ response to lake depth, thermal layers and TSISD values. The zooplankton SR and SI (during daylight hours) depends greatly on the mixing type. Lake type also indicates the importance of the metalimnion in shaping zooplankton biodiversity in dimictic lakes. In addition, data from NW Polish lakes indicated that the increase of the TSISD leads to taxonomic shifts and has a negative effect on the diversity of all groups of zooplankton

Impact of the catchment land use on some factors of lakes trophic status: a GIS approach

ABSTRACT Background. Artificial enrichment of lakes has posed serious management problems for water supply. In results many European lakes had already undergone significant eutrophication. It seems that a good tool to determine the influence of catchment use on the trophic changes in lakes is Geographic Information System (GIS) and its databases. Methods. The study covered 31 stratified lakes located in northwestern Poland. These lakes were chosen on account of their considerable recreation value and economic importance. The parameters chosen as dependent variables were Secchi depth and electrical conductivity. Local catchments and network catchment of studied lakes as independent variables were prepared using QGIS Wien (2.8.7). The land use variables were prepared with Corine Land Cover, 2006. Results. According to Carlson index the studied lakes ranged from mesotrophic to eutrophic. Both dependent variables Secchi depth and conductivity values were significantly correlated with independent land use variables (P < 0.05). Discussion. Our survey revealed that percentage use of the catchment (developed in the Geographic Information System) can be a useful tool in the assessment of the lakes risks. With the GIS tools we also confirmed a significant impact of land use on changes transparency and conductivity values in North West lakes in Poland

Contrasting responses of Thermocyclops crassus and T. oithonoides (Crustacea, Copepoda) to thermal stress

Abstract Thermal tolerance is a critical factor influencing the survival of living organisms. This study focuses on the thermal resistance of copepod species, Thermocyclops crassus (Fischer, 1853) and T. oithonoides (Sars G.O., 1863), with overlapping distribution ranges in Europe. Short-term heat shock experiments were conducted to assess the thermal resistance of these copepods, considering various temperature increments and exposure durations. Additionally, the study explored the influence of heat shock on egg sac shedding, a vital indicator of population dynamics. Results indicate that widely distributed T. crassus exhibits higher thermal tolerance compared to narrowly distributed T. oithonoides, with survival rates varying under different heat shock conditions. Furthermore, T. crassus demonstrated a quicker response in dropping egg sacs in response to thermal stress, suggesting a potential adaptive mechanism for the survival of adults. However, rapid egg sac droppings pose high risks for eggs facing unfavorable conditions. T. crassus, inhabiting environments with greater temperature fluctuations such as the littoral and pelagial zones, exhibited better survival mechanisms compared to T. oithonoides, which predominantly resides in the pelagic zone. The findings have implications for understanding copepod responses to global warming and thermal pollution. This research contributes insights into the adaptive strategies of thermophilic copepod species and their ecological consequences

Insights into the morphology and molecular characterisation of glacial relict Eurytemora lacustris (Poppe, 1887) (Crustacea, Copepoda, Calanoida, Temoridae)

Eurytemora lacustris (Poppe, 1887) is a stenothermic glacial relict whose narrow environmental requirements make it an indicator species for good ecological conditions. The primary threats to this species are eutrophication and global warming. Many authors have described E. lacustris in taxonomic keys; however, its morphological description is unsatisfactory. Therefore, in this study, we aimed to review morphological characteristics of E. lacustris that were previously undescribed in the literature and to provide the molecular characteristics based on the two conservative mitochondrial genes: cytochrome c oxidase I (COI) and cytochrome b (cytb). The new record of E. lacustris indicates that it is a more widespread species than previously hypothesized. Width-to-length ratio of the last female endopod segment of legs indicates variation among the widely distributed species of the genus in Europe (i.e., E. lacustris, E. velox (Lilljeborg, 1853), and E. affinis (Poppe, 1880)). We also found variability of number of setae on the second segment of male endopod. Furthermore, our analysis confirms the occurrence of species in different than exclusively freshwater habitats