Resistance to low oxygen in the Ponto–Caspian amphipod Pontogammarus robustoides varies among lentic habitats of its northern invaded range

The Ponto–Caspian amphipod Pontogammarus robustoides was introduced into Lithuanian inland waters more than 50 years ago and is now among the most successful local crustacean invaders. Existing as an oxyphilic species in its native range, in Lithuania it managed to establish in some lentic eutrophic waters facing long-term hypoxic conditions under winter ice cover, or shorter periods of hypoxia during the warm season. Recently, it has been observed to be further expanding in such waters. The aim of this study was to explore the possible divergence in anaerobic metabolism among introduced populations facing different selective pressures. A closed-bottle experiment was conducted using individuals from three Lithuanian lentic water bodies of different trophic status: mesotrophic, eutrophic and hypertrophic. Severe hypoxia was gradually reached, after which lactate dehydrogenase activity was significantly higher in amphipods from eutrophic and hypertrophic, than from mesotrophic environments, and was well correlated with trophic status of inhabited environments as assessed by chlorophyll a concentration. These findings suggest a physiological acclimation response to oxygen deficiency faced by the species in some environments in the northern invaded range, which may have a genetic background. Such resistance to oxygen deficiency may expand the environmental niche and promote species’ spread into previously unsuitable habitats, which may pose a threat to native species residing in refuges that are currently free of the invader

First record of Dikerogammarus bispinosus Martynov, 1925 in Kazakhstan: invasive or overlooked native in the Caspian Sea basin?

The Ponto-Caspian amphipod Dikerogammarus bispinosus is regarded as a native species throughout the lower stretches of rivers that drain into the Black Sea. Its occurrence in the Caspian Sea basin was uncertain due to conflicting reports. Here, we provide the first conclusive evidence for its presence in this basin. Individuals of both sexes, including ovigerous females, were collected in May 2000 from the Ural River in Kazakhstan, suggesting full establishment. If it was a recent invasion, the most probable dispersal pathway into the Caspian basin would have been via the Volga-Don canal as D. bispinosus was reported in the early 2000s from the lower Don River and the Saratov reservoir on the Volga River. However, given that until relatively recently D. bispinosus was considered a subspecies of D. villosus, we cannot rule out that it has been overlooked in earlier reports from the Caspian Sea basin by being mentioned as D. villosus or even D. haemobaphes. We also provide new data on the distribution of Gammarus lacustris, Obesogammarus platycheir, Pontogammarus abbreviatus, P. robustoides, Turcogammarus aralensis and Wolgagammarus dzjubani in western Kazakhstan and southwestern Russia

Does the Ice Age legacy end in Central Europe? The shrinking distributions of glacial relict crustaceans in Lithuania

Glacial relict crustaceans are characterized by their affinity for cold and well-oxygenated waters and their limited dispersal ability. They occur in large, deep lakes of Northern and Central Europe and North America, with their distributions shaped by glaciation events. In many countries and especially along the southern distribution edge, glacial relict populations are declining as a result of eutrophication, global warming, and possible adverse interactions with invasive Ponto-Caspian crustaceans. This study assessed the status of three glacial relict malacostracan species (the amphipods Monoporeia affinis and Pallaseopsis quadrispinosa and the mysid Mysis relicta) in Lithuania and modelled their abundance across environmental variables, including the presence of Ponto-Caspian malacostracans. The results showed that M. affinis is probably extinct in the country, whereas M. relicta was found in only nine out of 16 locations from which it was previously recorded. The distribution of P. quadrispinosa also seems to be shrinking. The annual water renewal rate (P. quadrispinosa and M. relicta) and lake depth (P. quadrispinosa) were significantly and positively associated with the relative abundance of relict mysids and amphipods, but no association was found with lake size or with the presence of invasive Ponto-Caspian crustaceans. Both species were less abundant in samples collected in the 21st century compared with the 20th century. Given the biogeographical and ecological importance of glacial relict crustaceans, their widespread declines are of concern and point to the deterioration of habitat quality, essential for other species with similar requirements. Urgent action is needed to improve water conditions and safeguard these communities. In cases where water quality improves, the reintroduction of extirpated relict populations should be considered. One example is Lake Drūkšiai, where these crustaceans became extinct during the operation of the Ignalina nuclear power plant but where conditions improved following the closure of the power plant in 2009