Planktonic rotifers in a subtropical shallow lake: succession, relationship to environmental factors, and use as bioindicators

Long-term succession characteristics and driving factors of zooplankton communities in a typical subtropical shallow lake, central China

Zooplankton community could be affected by aquatic environment, land use patterns, and climate factors. However, few studies have evaluated the relative importance of these factors to the zooplankton community succession on a long-term scale. In this study, long-term data were used to analyze the succession characteristics and drivers of zooplankton communities in Honghu Lake, a large-scale shallow lake in central China. Results showed that zooplankton community structure changed greatly in 1959-2021. In general, the species number decreased, abundance and biomass increased, and the number and proportion of pollution tolerant species among dominant species increased during the past ~ 60 years. For the driving factors of zooplankton from 1992 to 2021, redundancy analysis showed that nutrients, wind speed, and aquaculture enclosure and pond were the main drivers of Protozoa and Rotifera, while phytoplankton abundance, wind speed, dissolved oxygen, and farmland were the main drivers of Cladocera and Copepoda. Generalized additive model showed that the aquatic environment had the highest direct explanation (mean is 60.2%) to zooplankton variation, followed by land use (mean is 35.6%) and climate factors (mean is 33.1%). Variance partitioning analysis showed that the effects of human activities (32.9-43.1%) associated with land use, water quality, and phytoplankton on the zooplankton succession are stronger than that of climate factors (19.9-29.2%). Additionally, lake eutrophication is an important factor for the decline in the richness index (p = 0.0017, r =  - 0.8411) and Shannon index (p = 0.0301, r =  - 0.8020) of zooplankton from 2019 to 2021. Our results highlighted that anthropogenic activity has stronger driving effects on zooplankton succession in the long term than climate changes in the lake. These findings can provide insights into zooplankton conservation in response to global climate change and complex anthropogenic actions.

High-throughput sequencing reveals omnivorous and preferential diets of the rotifer Polyarthra in situ

Knowledge of in situ diet of widespread rotifers is crucial for accurately understanding the trophic position, ecological function, and adaptability to environmental changes in aquatic ecosystems. However, it is challenging to achieve the in situ diet information due to the lack of efficient and comprehensive methods. Here, we investigated the diet composition of Polyarthra in a subtropical lake using high-throughput sequencing (HTS) of a rRNA metabarcode for Polyarthra and ambient water samples. After eliminating Polyarthra sequences, a total of 159 operational taxonomic units (OTUs) from taxa in 15 phyla were detected from Polyarthra gut content samples. Most of the OTUs belong to Chlorophyta, followed by unclassified Fungi, Chrysophyta, Dinoflagellata, Ciliophora, Bacillariophyta, Cryptophyta, Arthropoda, Cercozoa, Mollusca, Apicomplexa, Haptophyta, Amoebozoa, Chordata and other eukaryotes. Our results showed that Polyarthra mainly grazed on Chlorophyta, which may result from the high relative abundance of Chlorophyta in ambient waters. In contrast, Chrysophyceae and Synurophyceae were enriched in Polyarthra's gut, indicating that this rotifer prefers these taxa as food. Moreover, correlation analysis showed that total nitrogen, transparency, depth, Chlorophyll-a and total phosphorus were key factors for the variation of the eukaryotic community in the Polyarthra gut contents. When the concentration of nutrients in the water environment decreased, Polyarthra shifted from herbivorous feeding to more carnivorous feeding. Thus, Polyarthra is generally omnivorous but preference for Chrysophytes and Synurophytes, and it responds to the environmental changes by adopting a flexible feeding strategy. This could partly explain why the widespread rotifers have apparently wide tolerance toward spatial and environmental changes.

The relationship between zooplankton community and environmental factors of Ghrib Dam in Algeria

The effect of environmental factors on zooplankton diversity, abundance, and distribution in the Ghrib Dam water body was investigated for 2 years from June 2013 to May 2015. A total of 61 species of zooplankton were recorded, including 45 rotifers, 13 cladocerans, and 3 copepods. The zooplankton abundance fluctuated between 4 and 3363 ind.L^-1, and its Shannon-Wiener index of zooplankton diversity in Ghrib Dam varied from H' = 1.15 to 3.77 during the 2-year study period. The highest diversity index was recorded at sampling site S1 in January 2015, due to the increase of specific richness (Ni = 27, D_mg = 5.75). Canonical correspondence analysis (CCA) was used to determine the influence of environmental factors in structuring the zooplankton species for each group. The results of CCA revealed that the most significant environmental factors influencing zooplankton community were water temperature (WT), dissolved oxygen (DO), phosphorus (PO₄^-), and NO₃^- (p < 0.05, Monte Carlo permutation test). Meanwhile, the appearance of Hexarthra sp., Collotheca pelagica, and Diaphanosoma brachyurum indicated a rise in WT. The existence of Filinia longiseta, Keratella quadrata, and Cyclops strenuus correlated with a rising of DO. Brachionus urceolaris, Filinia passa, Keratella tecta, Notholca acuminata, and Polyarthra dolichoptera positively coexisted in an increased PO₄^-. Daphnia longispina and Oxyurella tenuicaudis were positively associated with high concentration of NO₃^-.

Key drivers structuring rotifer communities in ponds: insights into an agricultural landscape

Understanding the influence of environmental and spatial factors on the structure of aquatic communities remains a major challenge in community ecology. This study aims to identify main drivers of rotifer abundance and diversity in ponds embedded in an intensive agricultural landscape in Northeast Germany. We studied 42 ponds of glacial origin (kettle holes) covering a wide range of environmental parameters. The predominant factors structuring the rotifer metacommunity shifted from abiotic environmental filtering in spring to unstudied factors in autumn, while spatial factors remained less important. Fertilizer-driven salinization, internal nutrient recycling, primary productivity and sediment phosphorus release were the prevalent biogeochemical processes in the ponds. Both fertilizer-driven salinization and primary productivity negatively affected rotifer alpha diversity, and positively affected beta diversity. This impact was lower in forest ponds than in those surrounded by arable fields or grassland. However, rotifer diversity did not significantly differ among land-use categories. Our results indicate that the long-term impact of intensive agriculture in the region and the associated widespread eutrophication overrides the direct influence of land use on rotifer diversity but point to an indirect effect via fertilizer-driven salinization. Furthermore, this study highlights the role of ponds in enhancing regional biodiversity in agricultural landscapes.

Influence of Hydrological Heterogeneity on Rotifer Community Structure in Three Different Water Bodies in Shantou Area, Guangdong (China)

Rotifers, small but essential invertebrates in aquatic ecosystems, are sensitive to environmental changes and are proposed to be indicators of trophic state. However, the effects of hydrological heterogeneity on the rotifer community and the ability of rotifer indices to reflect trophic state across different water bodies are still unclear. Here, we investigated rotifer community structure in different seasons in the three types of water bodies: Han river downstream (HD), Reservoir (RE) and Tidal creek (TC) in Shantou City, Guangdong, China. Our findings revealed that rotifer community structure differes significantly among the three water bodies, resulting from a dominance of Keratella cochlearis, Anuraeopsis fissa and Polyarthra vulgaris, who largely accounted for the differences in water bodies. Chlorophyll-a and transparency were the main environmental drivers in RE rotifer communities, while total nitrogen, total phosphorus and salinity were the main factors in HD and TC communities. Rotifer abundance and the rotifer trophic state index decreased in the order: RE > HD > TC. However, both the Sladecek's B/T quotient and the Keratella- index decreased in the order: HD > RE > TC, which was in accordance with the Carlson's trophic index. We conclude that it is efficient to use rotifer composition in water quality assessments when comparing different water bodies. Alpha diversity of rotifers was the highest in HD, which is consistent with the intermediate disturbance hypothesis. Hydrological heterogeneity is the micro-factor that regulates rotifer community structures in the Shantou area.

Comprehensive approach to restoring urban recreational reservoirs. Part 2 - Use of zooplankton as indicators for the ecological quality assessment

The presented research is part of the LIFE project ("EH-REK" LIFE08 ENV/PL/000517) on innovative restoration methods for small urban impoundments in the city of Łódź (Poland). The objective was to evaluate the usefulness of zooplankton as a biological quality element, when assessing the effectiveness of restoration efforts in three urban reservoirs and a one pond. The fifth unrestored pond was used as an example of the progressive eutrophication of an urban ecosystem. Studies were conducted during two periods: before (2010-2012) and after (2013-2016) restoration. A selection of zooplankton indices, including the rotifer trophic state index (TSI_ROT), was used. The influence of the supplying river resulted in the negligible responses of biological parameters to the restoration efforts in the Upper Arturówek (UA) reservoir, which is the first in cascade of reservoirs. However, clear symptoms of water quality improvements were observed in the other two reservoirs (the Middle Arturówek, MA; the Lower Arturówek, LA) and in the Bzura-17 (B17) pond. After restoration, the contribution of species indicative of high trophic levels decreased in these ecosystems. The TSI_ROT was strongly positively correlated with the trophic state index based on chlorophyll a, and both parameters significantly decreased in the MA, LA and B17. In the unrestored pond (B11), the successive increase in the concentrations of chemical parameters indicated progressing eutrophication. Interestingly, since 2013, the TSI_ROT values clearly decreased in B11, but the strong negative correlation between ammonium concentration and rotifer density indicated that the reduced TSI_ROT values didn't result from improvements in water quality; rather, they resulted from the increases in pollution and the associated harmful impacts on Rotifera. In conclusion, the TSI_ROT can be a useful tool for assessing the ecological quality of small urban ecosystems; however, the use of biological indices must be supported by also monitoring physicochemical parameters.