Trematode cercariae as prey for zooplankton: effect on fitness traits of predators

Removal of parasite free-living stages by predators has previously been suggested an important factor controlling parasite transmission in aquatic habitats. Experimental studies of zooplankton predation on macroparasite larvae are, however, scarce. We tested whether trematode cercariae, which are often numerous in shallow waters, are suitable prey for syntopic zooplankters. Feeding rates and survival of freshwater cyclopoids (Megacyclops viridis, Macrocyclops distinctus), calanoids (Arctodiaptomus paulseni), cladocerans (Sida crystallina) and rotifers Asplanchna spp., fed with cercariae of Diplostomum pseudospathaceum, a common fish trematode, were studied. In additional long-term experiments, we studied reproduction of cyclopoids fed with cercariae. All tested zooplankton species consumed cercariae. The highest feeding rates were observed for cyclopoids (33 ± 12 cercariae ind−1 h−1), which actively reproduced (up to one egg clutch day−1) when fed ad libitum with cercariae. Their reproductive characteristics did not change significantly with time, indicating that cercariae supported cyclopoids’ dietary needs. Mortality of rotifers and cladocerans was high (25–28% individuals) when exposed to cercariae in contrast to cyclopoids and calanoids (<2%). Cercariae clogged the filtration apparatus of cladocerans and caused internal injuries in predatory rotifers, which ingested cercariae. Observed trophic links between common freshwater zooplankters and cercariae may significantly influence food webs and parasite transmission in lentic ecosystems.

Should I stay or should I go? The diurnal behaviour of plant-attached zooplankton in lakes with different water transparency

<p>The role of transparency on the diurnal distribution of plant-attached cladocerans was studied in two similar-sized lakes with contrasting water colour. The diurnal attachment behaviour of <em>Sida crystallina</em> (O.F. Müller, 1776) was more pronounced in the less humic lake where the animals remained fixed on plants, indicating that staying attached was a more profitable option. In the highly humic lake, the pattern was opposite, and regardless of time the highest density observed was in the free-swimming individuals, with only few animals attached to the floating-leaves for refuge, indicating that low transparency provided sufficient protection against predation. The attached <em>S. crystallina</em> were larger compared to free-swimming individuals in the more transparent lake, suggesting greater vulnerability of large-sized individuals to predation. The results indicate that increasing concentrations of humic substances affecting the light environment may alter the diurnal behaviour and habitat use of plant-attached zooplankton. </p>

The occurrence of the new zooplankton species in the Lena river delta

The Lena River impact on the water bodies of its catchment area increases in connection of climate warming. During spring floods the river water enters the numerous floodplain water basins, further promotes the passive dispersal of their fauna in the northern direction. The occurrences of new (for the local fauna) zooplankton species repeatedly documented in the lakes on Samoylov Island in the south part of the Lena Delta over the last 15 years. Seven “invasive species” belong to Cladocera, four to Copepoda and one species of Rotifera. Some cladocerans –Sida crystallina (O.F. Muller, 1776), Limnosida frontosa (Sars, 1862), Diaphanasoma brachyurum (Lievin, 1848) and Polyphemus pediculus (Linnaeus, 1761) – several times appeared and disappeared in the floodplain aquatic habitats on Samoilovsky Island during the observation period. Simocephalus vetulus (O.F. Muller, 1776) found conditions here to be favorable and formed the local population in the floodplain pools. Acroperus harpae (Baird, 1834) and Holopedium gibberum Zaddach, 1855 started to settle from low floodplain in neighboring water ecosystems of the first delta terrace with a height of 10–16 m. The spread of resting stages of zooplankton are likely to occur with the participation of waterfowl. In years with extremely high spring tide, the expansion of species, not typical for the area, was of a catastrophic nature. A massive invasion of certain species, for example Holopedium gibberum Zaddach, 1855, can cause a rapid restructuring of the lake biocoenosis and disturb the ecological balance in it, resulting in parasitic epizootic.

Cladocera (Crustacea: Branchiopoda) of the south-east of the Korean Peninsula, with twenty new records for Korea

We studied the cladocerans from 15 different freshwater bodies in south-east of the Korean Peninsula. Twenty species are first records for Korea, viz. 1. Sida ortiva Korovchinsky, 1979; 2. Pseudosida cf. szalayi (Daday, 1898); 3. Scapholeberis kingi Sars, 1888; 4. Simocephalus congener (Koch, 1841); 5. Moinodaphnia macleayi (King, 1853); 6. Ilyocryptus cuneatus Štifter, 1988; 7. Ilyocryptus cf. raridentatus Smirnov, 1989; 8. Ilyocryptus spinifer Herrick, 1882; 9. Macrothrix pennigera Shen, Sung & Chen, 1961; 10. Macrothrix triserialis Brady, 1886; 11. Bosmina (Sinobosmina) fatalis Burckhardt, 1924; 12. Chydorus irinae Smirnov & Sheveleva, 2010; 13. Disparalona ikarus Kotov & Sinev, 2011; 14. Ephemeroporus cf. barroisi (Richard, 1894); 15. Camptocercus uncinatus Smirnov, 1971; 16. Camptocercus vietnamensis Than, 1980; 17. Kurzia (Rostrokurzia) longirostris (Daday, 1898); 18. Leydigia (Neoleydigia) acanthocercoides (Fischer, 1854); 19. Monospilus daedalus Kotov & Sinev, 2011; 20. Nedorchynchotalona chiangi Kotov & Sinev, 2011. Most of them are illustrated and briefly redescribed from newly collected material. We also provide illustrations of four taxa previously recorded from Korea: Sida crystallina (O.F. Müller, 1776); Macrothrix rosea (Jurine, 1820); Bosmina (Bosmina) longirostris (O. F. Müller, 1776) and Disparalona cf. hamata (Birge, 1879). Among the newly recorded taxa, there are six Far East endemics; five tropicopolitan species for which the Amur basin is the northernmost margin of their distribution; four tropicopolitan species for which Korea is presumed to be the northern most area of their distribution; two Palaearctic taxa for which Korea could be the southern most area of their distribution; two cosmopolitan species which need to be revised; and one species widely distributed in Eastern Asia. Despite significantly increasing the number of known species of cladocerans in Korea, we recognize that further research is needed to complete the picture, and the cosmopolitan taxa need further revision.

Overview of Sididae (Crustacea: Cladocera: Ctenopoda) of Northeast and East Thailand, with description of a new species of the genus Diaphanosoma

The investigation of an extensive collection of zooplankton samples from Northeast and East Thailand has revealed 10 species of the family Sididae, members of which often were mostly frequently distributed and abundant among Cladocera. Of seven species of the genus Diaphanosoma, one is new to science (D. elongatum sp. nov.) and two others, D. senegal and D. macrophthalma, new to Thailand. The genus Pseudosida is represented by P. szalayi instead of P. bidentata incorrectly recorded previously. Eleven species of Sididae are now known from Northeast Thailand and 12 from the whole country. The highest frequency occurrence and abundance were observed in D. excisum, D. dubium, Latonopsis australis, and P. szalayi while other species were more infrequent (D. sarsi) or rare. Sididae species were often observed co-occurring in different combinations, among them up to three-four species of Diaphanosoma. The rare species D. senegal frequently co-occurred with large Branchiopoda. Most Sididae of Northeast Thailand are of tropical origin while others (D. dubium, D. macrophthalma, Sida crystallina) have penetrated here from more northern latitudes.