Morphological characteristics of Kellicottia bostoniensis (Rousselet, 1908) (Rotifera: Brachionidae) in water bodies of the Middle Volga basin

The morphological characteristics of the North American invasive species Kellicottia bostoniensis Rousselet, 1908 were studied in 29 various types of water bodies and watercourses of the Middle Volga basin. The water bodies, which are the habitats of K. bostoniensis, are located on several territories that differ significantly in a set of characteristics, such as their geological structure, relief, climate, anthropogenic impact, hydrochemical and hydrophysical indicators, etc. The sizes of K. bostoniensis individuals in most of the studied water bodies and watercourses were measured and analyzed for the first time. A high positive correlation was found between the total body length and the posterior spine length (R2 = 0.79, p < 0.01), as well as the anterior spine length (R2 = 0.75, p < 0.01). A relationship was revealed between the lengths of the anterior and posterior spines (R2 = 0.58, p < 0.01). K. bostoniensis individuals in the studied water bodies and watercourses are characterized by large sizes, the median values of the total body length being 236–440 μm. These sizes are similar to those of individuals in the native habitats of North America and some biotopes of Europe and European Russia. Among the previously studied water bodies of Russia and other countries (Belarus, Sweden, Finland, Brazil, and Argentina), where researches of the morphological variability of K. bostoniensis were carried out, the largest body sizes were characteristic for the invader species of the Sura River. Larger K. bostoniensis specimens live in deep mesotrophic water bodies with high transparency, compared with representatives of this species in shallow eutrophic water bodies with less transparency in the Middle Volga basin. Our data on the morphological characteristics of the invading species of water bodies in the Middle Volga basin significantly expand the existing information on the morphological variability of K. bostoniensis individuals and their dependence on environmental factors.

ABUNDANCE OF RELATED SPECIES, KELLICOTTIA BOSTONIENSIS (ROUSSELET, 1908) AND K. LONGISPINA (KELLICOTT, 1879) (ROTIFERA: BRACHIONIDAE), IN THE COMMUNITIES OF ZOOPLANKTON OF THE PUSTYNSKAYA LAKE-RIVER SYSTEM (NIZHNY NOVGOROD OBLAST)

The article presents the features of the spatial distribution of zooplankton communities in the water area of the Pustynskaya lake-river system. The abundance of two related species of the genus Kellicottia , the alien Kellicottia bostoniensis (Rousselet, 1908) and the indigenous K. longispina (Kellicott, 1879), was analyzed in dedicated communities in 2013-2017. The greatest abundance of the alien species was noted in zooplanktocenoses of mesotrophic water bodies (the Serezha River and Lake Svyato). It was found that after the period of mass development of K. bostoniensis in 2013-2014, which might be due to the initial stage of naturalization of the alien species, its abundance had sharply decreased. In 2013-2014 the abundance of the indigenous species K. longispina (Kellicott, 1879) was significantly lower than that of the alien species. Rotifer K. longispina dominated in the Protoka and Lake Svyato in 2017. The highest density of both species was found in the metalimnion of the mesotrophic Lake Svyato. A statistically significant positive correlation was found between the abundance of K. bostoniensis and the temperature, transparency, and pH of water, as well as the abundance of predatory zooplankton species. The abundance of the native species K. longispina correlated negatively only with the value of water pH.

Functional groups of rotifers and an exotic species in a tropical shallow lake

In freshwater environments the rotifer group may be divided into microphagous and raptorial species regarding their feeding patterns, and such guilds differently interact with other community components. Here, we analyzed the influence of cladocerans, cyclopoid nauplii, temperature, food resources and an exotic species on rotifer guilds, based on weekly samplings for 1 year. We have identified rotifer species and their trophi types in order to separate them into the raptorial and microphagous functional groups. The ratio raptorial:microphagous rotifers (Guild ratio, GR) was used in interaction analyses with cladocerans, nauplii, temperature, food resources and the exotic species Kellicottia bostoniensis. Correlations between total rotifers and food (phytoplankton carbon) and temperature were negative and significant, therefore, these factors did not lead to the increase of rotifer community. On the other hand, microphagous rotifers had opposing relation to cladoceran densities, as GR values showed that they became predominant when cladoceran populations declined. The use of density-based GR was adequate, with similar results compared to biomass-based studies regarding interactions with other organisms. Furthermore, we have found no invasive characteristics for the exotic microphagous rotifer, Kellicottia bostoniensis, and it seems to be outcompeted by the native microphagous species.

Zooplankton communities and their relationship with water quality in eight reservoirs from the midwestern and southeastern regions of Brazil

Zooplankton are widely recognised as being regulated primarily by predators and food availability. In reservoirs, the quantity and quality of food resources are generally affected by the characteristics of the water, which in turn are controlled by the flow pulse generated by operation of the dams. In this study, we investigated the relationship between zooplankton, water quality and food availability (phytoplankton) in eight hydroelectric reservoirs located in Brazil. Samples were collected during the rainy and dry periods between 2008 and 2009. In general, the reservoirs exhibited mesotrophic conditions and Cyanobacteria were the predominant phytoplankton. The results showed that the rotifers Kellicottia bostoniensis, Hexarthra mira, Keratella spp., and Polyarthra vulgaris were present, indicating nutrient-rich environments. In addition, the copepod Thermocyclops decipiens occurred in eutrophic environments. In contrast, the cladoceran Daphnia gessneri and copepod Notodiaptomus henseni were considered indicators of more desirable water quality, owing to their relationship with waters with lower levels of nutrients and suspended solids. The results support the use of these organisms as a useful tool for understanding changes in water quality and in the ecosystem processes involved.

Composition and richness of monogonont rotifers from La Plata River Basin, South America

We present here the first study that analyzed the composition and richness of rotifers of the entire La Plata River basin, the second largest in South America, based on simultaneous and standardized sampling. Fifteen large reservoirs and eight river stretches were selected in the upper, middle, and lower portions of the Paraná, Paraguay, and Uruguay Rivers, which are the major rivers of the La Plata basin. We took a total of 86 samples (open water habitats) in 2010. A mean of 27±11 species per sub-basin was found, with the highest richness in the Lower Paraná (41 species), followed by the Paranapanema (40 species) and Lower Uruguay (38 species). Low richness was observed in the Middle Uruguay and Middle Paraná. We found 106 species belonging to 21 families and two orders. The family with the highest number of species was Lecanidae (21), followed by Brachionidae (20), Trichocercidae (9), and Synchaetidae (8). The species with higher occurrences were Conochilus dossuarius, Kellicottia bostoniensis, Keratella americana, Keratella cochlearis and Hexarthra mira. New occurrences of rotifers were registered for Brazil (Colurella adriatica), São Paulo State (Enteroplea lacustris), and Argentina (Gastropus hyptopus, Harringia rousseleti and Lecane thienemanni). Spearman correlation between the number of species and physical and chemical variables demonstrated positive correlation with chlorophyll and temperature, and negative correlation with dissolved oxygen. We extend the distribution list for some native (Lecane ludwigii) and non-native species of rotifers (K. bostoniensis). We also list the monogonont rotifer species found at the sampling stations.