The Use of Winter Water Temperature and Food Composition by the Copepod Cyclops vicinus (Uljanin, 1875) to Provide a Temporal Refuge from Fish Predation

Frequent predation induces various defense strategies in prey, including morphological changes or migration patterns in zooplankton. We hypothesized that the winter dominance of Cyclops vicinus in the Upo Wetlands, South Korea, is an evolved temporal defense mechanism to avoid fish predation. Long-term data (2014–2019) showed that fish consumed the most cyclopoid copepods from spring to autumn. Lepomis macrochirus preferentially consumed C. vicinus; thus, C. vicinus density was lower from spring to autumn. However, C. vicinus was abundant in winter when fish consumed fewer copepods. Nauplii density began to increase in late autumn (October–November), and their population growth was fueled through consumption of Cyclotella sp. and Rhodomonas sp. Culture experiments showed that Cyclotella sp. contributed more to the growth stage (copepodite or subadult) after nauplii than Rhodomonas sp. C. vicinus density was lower in the winters of 2013 and 2016 when the densities of these phytoplankton prey species were lower. In summary, although winter conditions were suitable for copepod survival and population growth, C. vicinus relied heavily on the diversity and species composition of its food sources. The winter dominance of C. vicinus could increase regional biodiversity and contribute significantly to the stability of the freshwater food web.

Diversity of Zooplankton in Lindu Lake Waters Central Sulawesi Province

Zooplankton is small animals that swim or float in water pools and significantly affect the life of lake aquatic organisms, especially as natural food in the development and cultivation of fish. The purpose of this study was to determine the diversity of Zooplankton species in the waters of Lake Lindu. This research was conducted in April - June 2019 using a purposive sampling method. The results obtained nine types of Zooplankton in the waters of Lake Lindu, Central Sulawesi Province, namely Daphnia sp, Epischura lacustris, Hyperia sp, Cyclops vicinus, Pseudophausia sp, Temora sp, Alonella dadayi, Nebela caudate, Brachionys havanaensis. The diversity of Zooplankton species found in the waters of Lake Lindu is 2.190 (moderate diversity level). The highest H value is at station III (Inlet) which is 2.175, and the lowest H 'value is at station II (settlements) of 2.149.

Grazing of the copepod Cyclops vicinus on toxic Microcystis aeruginosa: potential for controlling cyanobacterial blooms and transfer of toxins

Grazing of zooplankton on phytoplankton may contribute to a reduction of harmful cyanobacteria in eutrophic waters. However, the feeding capacity and interaction between zooplankton and toxic cyanobacteria vary among grazer species. In this study, laboratory feeding experiments were designed to measure the grazing rate of the copepod Cyclops vicinus on Microcystis aeruginosa and the potential microcystin (MC) accumulation in the grazer. Copepods were fed a mixed diet of the edible green alga Ankistrodesmus falcatus and toxic M. aeruginosa for 10 days. The results showed that C. vicinus efficiently ingested toxic Microcystis cells with high grazing rates, varying during the feeding period (68.9–606.3 Microcystis cells animal-1 d-1) along with Microcystis cell density. Microcystis cells exhibited a remarkable induction in MC production under grazing conditions with concentrations 1.67–12.5 times higher than those in control cultures. Furthermore, C. vicinus was found to accumulate MCs in its body with concentrations increasing during the experiment (0.05–3.21 μg MC animal-1). Further in situ studies are needed to investigate the ability of Cyclops and other copepods to assimilate and detoxify MCs at environmentally relevant concentrations before deciding on the biocontrol of Microcystis blooms by copepods.

Zooplankton in a Danube River Arm near Rusovce (Slovakia)

Poor quantity of zooplankton was recorded in a Danube arm situated on the right side of the Danube River in Slovakia (river km 1857) in 2002 and 2003. All over the year the arm is significantly influenced by groundwater by reason of seepage. Because of low mean water temperature (12°C) and poorly developed macrovegetation in particular, the arm reminds gravel pit-like. The annual average of zooplankton biomass was low and ranged from 0.35 g m−3 (2002) to 1.28 g m−3 (2003), because of low crustacean abundance. Total cladoceran abundance was excessively low in both years and ranged from 3.5 N L−1 (2002) to 16.6 N L−1 (2003). Small species, Bosmina longirostris and Chydorus sphaericus were dominant. Only four adult Copepoda — Cyclops vicinus, Thermocyclops crassus, Eurytemora velox and Eudiaptomus gracilis — were recorded in quantitative samples of both years. In the zooplankton assemblage dominated rotifers (Synchaeta pectinata, Synchaeta oblonga, Polyarthra dolichoptera and Keratella cochlearis) which represented 78% and 67% of total abundance respectively. The total of 19 species of rotifers, 34 Cladocera species and 16 taxa of Copepoda were found.