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Signal crayfish (Pacifastacus leniusculus (Dana, 1852)) are among the most invasive macroinvertebrates in Europe, representing economic value as well as serious threats to ecosystems. Despite decades of research, uncertainties with respect to its biology remain. The present study describes the observations of adult signal crayfish during a single growing season, with a sex ratio of 1:1, reared under natural ambient conditions, in which moulting events, growth increments, morphological changes, mortality, and reproductive output were monitored. Two moults were observed in the majority of both sexes, with significant differences in moult growth increments of once- and twice-moulted animals. These led to modifications in morphology during the growing season. Females showed isometric growth at the first moult, while, at the second moult, they strengthened the functional state of structures linked to reproduction. In males, the effect was similar, but to a lesser extent, with extensive chelae development at the second moult. There were no differences in relative fecundity of once- and twice-moulted females. However, signal crayfish have different needs during the growing and reproductive seasons. The presented results indicate the ability to use resources according to current needs (development of strategical body parts) via their seasonal morphological plasticity as seen in representatives of the family Cambaridae.

The success of non-native species establishment depends on various abiotic and biotic factors that determine the outcome of an introduction event. Limiting temperature ranges have been studied for various non-native species; however, such previous assessments of species-specific temperature thresholds may be inadequate. Because several non-native crayfish species prefer warmer water temperatures, introductions were generally assumed to occur during preferable, warmer periods. However, despite the generality, traditionally considered ‘warm-water’ species are gradually appearing in new habitats, which were previously considered too cold for successful establishment. Newly discovered overwintering abilities of these species are likely related to the winter stratification in lentic ecosystems, which maintain tolerable conditions. To understand better the survivability of two such non-native species, red swamp crayfish Procambarus clarkii and marbled crayfish Procambarus virginalis individuals were abruptly subjected to a thermic shock which lowered the water temperature from 20 °C (room temperature) to 6 °C, 4 °C and 2 °C, thus mimicking the release by pet owners during various phases of winter. The survival rate and foraging activity were monitored for up to 98 days. Procambarus clarkii showed a considerable higher survival rate at low temperatures (4 °C, 2 °C) compared to that of P. virginalis with neither sex nor size differences evident. Our findings reveal the ability of warm water invaders to withstand a shock during introduction at low temperature periods without acclimation. Considering these newly discovered shifts in physiological limitations, particularly for the red swamp crayfish, this may indicate a higher threat for areas with colder conditions.

Severe weather events, such as long‐term droughts, are challenging for many freshwater species. To survive drought, freshwater crayfish tend to inhabit shelters or burrows where they can remain in contact with water or high humidity environments. However, it is not known whether embryogenesis or post‐embryonic development can occur without free standing water. To address this question, three experiments were conducted using artificial burrows with high air humidity and using marbled crayfish (Procambarus virginalis Lyko, 2017) as a model species. Marbled crayfish are capable of parthenogenetic reproduction, burrow extensively and are able to travel long distances over land. In the first experiment, ovigerous females were transferred to simulated burrows without free water, but with high air humidity. A control group of females were kept in burrows with free water. Successful hatching was achieved in both groups. In the second experiment, ovigerous females were transferred to simulated burrows with no free water but high air humidity and post‐embryonic development were observed. Following successful hatching, offspring moulted to the second developmental stage (stage 2 juveniles). Stage 2 juveniles remained viable without free water for 20 days, but further development was not observed. However, when some of these stage 2 juveniles were placed back into fully aquatic conditions (experiment 3), they moulted to stage 3 within 4 to 8 days. These results demonstrated the ability of marbled crayfish to undergo terminal phases of embryogenesis, including hatching, as well as early post‐embryonic development under high air humidity conditions only. Post‐embryonic development was suspended in the absence of free water, and successfully resumed when re‐immersed. This similar ability to tolerate drought‐like conditions during post‐embryonic development may also occur in other crayfish species, especially primary burrowers. This unprecedented life history trait may be crucial for inhabiting ecosystems with rapidly changing water regimes. In drying climates, it may confer advantages on some crayfish species (including some invasive species) over others.

Environmental conditions have a major impact on swim bladder inflation (SBI) in intensively cultured pikeperch Sander lucioperca, but there is currently no evidence of SBI inflation failure under natural conditions. The goals of this study were to quantify SBI failure in pond-cultured pikeperch larvae and to investigate whether pond conditions and characteristics including surface area, average depth, submerged and littoral vegetation, or bottom substrate play a significant role in its occurrence. Pikeperch larvae (n = 5700) in 19 ponds were examined for SBI at 16 days post-hatching. The swim bladder (SB) failed to inflate in 243 (4.2%) of the larvae with incidence of non-inflation ranging from 0 to 17.6% in individual ponds. No significant differences were found in total length (P > 0.27) or weight (P > 0.14) of larvae with and without inflated SB. The proportion of larvae with successfully inflated SB was significantly influenced by the presence of littoral vegetation and by interaction of presence of littoral vegetation with pond surface area and with pond average depth. Fish in ponds lacking littoral vegetation with water depth

Freshwater ecosystems worldwide are facing the establishment of non-native species, which, in certain cases, exhibit invasive characteristics. The impacts of invaders on native communities are often detrimental, yet, the number and spread of non-native invasive species is increasing. This is resulting in novel and often unexpected combinations of non-native and native species in natural communities. While the impact of invaders on native species is increasingly well-documented, the interactions of non-native invaders with other non-native invaders are less studied. We assessed the potential of an invasive amphipod, the killer shrimp Dikerogammarus villosus (Sowinsky, 1894), to cope with other established invaders in European waters: North American crayfish of the Astacidae family—represented by signal crayfish Pacifastacus leniusculus (Dana, 1852), and the Cambaridae family—represented by marbled crayfish Procambarus virginalis Lyko, 2017. The main goal of this study was to investigate if killer shrimp, besides their role as prey of crayfish, can significantly influence their stocks by predating upon their eggs, hatchlings and free-moving early juveniles. Our results confirmed that killer shrimp can predate on crayfish eggs and hatchlings even directly from females abdomens where they are incubated and protected. As marbled crayfish have smaller and thinner egg shells as well as smaller juveniles than signal crayfish, they were more predated upon by killer shrimp than were signal crayfish. These results confirmed that the invasive killer shrimp can feed on different developmental stages of larger freshwater crustaceans and possibly other aquatic organisms.

The direct effects of temperature increases and differences among life-history might affect the impacts of native and invasive predators on recipient communities. Comparisons of functional responses can improve our understanding of underlying processes involved in altering species interaction strengths and may predict the effect of species invading new communities. Therefore, we investigated the functional responses of the mourning gecko Lepidodactylus lugubris (Duméril & Bibron, 1836) to explore how temperature, body-size and prey density alter gecko predatory impacts in ecosystems. We quantified the functional responses of juvenile and adult geckos in single-predator experiments at 20, 23 and 26 °C. Both displayed saturating Type-II functional responses, but juvenile functional responses and the novel Functional Response Ratio were positively affected by temperature as juvenile attack rates (a) increased as a function of increased temperature. Handling times (h) tended to shorten at higher temperature for both predator stages. We demonstrate that the effects of temperature on functional responses of geckos differ across ontogeny, perhaps reflecting life-history stages prioritising growth and maturation or body maintenance. This indicates that temperature-dependent gecko predatory impacts will be mediated by population demographics. We advocate further comparisons of functional responses to understand the invasiveness and future predatory impacts of geckos, and other invasive species globally, as temperatures change.

Spawning substrate is a critical factor in reproduction of commercially valuable percids. Substrate preferences of pikeperch Sander lucioperca were investigated using three types of artificial spawning substrates: long fibred brush, artificial turf and smooth plastic. There was a significantly higher preference for the brush nest, with thick rigid structures, than for artificial turf, while plastic nests remained unoccupied. The majority of pikeperch pairs (94.4%) spawned within 14 days of the beginning of the experiment. No difference was observed between substrates in time from stocking of fish to nest occupation and spawning. After egg laying, nests were moved to controlled conditions of a recirculation aquaculture system for incubation. Hatching rate and larva production did not differ significantly among tested substrates. Either used substrate was suitable for spawning and incubation in a recirculation aquaculture system. Obtained results can be used for semi‐artificial reproduction as well as for the support and control of wild pikeperch stocks in natural habitats.

The red-rimmed melania Melanoides tuberculata (O. F. Muller) has been used in the aquarist trade and biocontrol programs, leading to its emergence outside its native range. Two populations of the red-rimmed melania occur in Slovakia. We investigated the morphometric features of mentioned populations and made a comparison. These two populations differ significantly in investigated features. Mean shell length of red-rimmed melania individuals from the Opatovce nad Nitrou was 14.7 mm, while the mean shell length of specimens from Piesťany was 24.4 mm (p

Man-made reservoirs are important fresh-water ecosystems as they are globally common and share features of both standing and running waters. In streams and lakes, crayfish are an important component of freshwater ecosystems due to their habitat- modifying behaviour, substantial size, omnivorous feeding and often high abundance; however, their trophic role in reservoirs is not known. We evaluated the distribution and diet of noble crayfish (Astacus astacus) in the canyon-shaped, oligotrophic Nýrsko reservoir in West Bohemia region, Czech Republic. Using stable isotope analysis, we quantified the trophic level of all major components of the reservoir food web and investigated seasonal isotopic variation and how the trophic role of noble crayfish varied with habitat and ontogeny. Crayfish were an important food source for both predatory and omnivorous fish and consumed food sources from multiple trophic levels, including detritus, algae, zoobenthos and other crayfish. Throughout ontogeny, crayfish had similar levels of carnivory, but cannibalism was more prevalent in adult crayfish, while juveniles and sub-adults fed more on other zoobenthos. Moreover, crayfish had high feeding plasticity in time, as the relative importance of dominant food sources varied with season. Their feeding plasticity was especially evident in crayfish populations from different habitats, which adapted their feeding strategy to local resources. In addition, pelagic source usage increased with the depth as detritus and algae usage decreased. Proportion of females increased with the depth, while population density showed a unimodal response to the depth gradient. These findings indicate that crayfish are indeed ecologically important species with both direct and indirect roles in the trophic web of this reservoir ecosystem. This study was supported by the Ministry of Education, Youth, and Sports of the Czech Republic (Projects CENAKVA – CZ.1.05/2.1.00/01.0024, and CENAKVA II – LO1205 under the NPU I Programme). We also thank two anonymous reviewers for helpful comments. The authors declare no potential sources of conflict of interest. This study was supported by the Ministry of Education, Youth, and Sports of the Czech Republic (Projects CENAKVA – CZ.1.05/2.1.00/01.0024, and CENAKVA II – LO1205 under the NPU I Programme). We also thank two anonymous reviewers for helpful comments. The authors declare no potential sources of conflict of interest.

Biological invasions are increasingly recognized ecological and economic threats to biodiversity and are projected to increase in the future. Introduced freshwater crayfish in particular are protruding invaders, exerting tremendous impacts on native biodiversity and ecosystem functioning, as exemplified by the North American spiny-cheek, signal and red swamp crayfish as well as the Australian common yabby. The marbled crayfish is among the most outstanding freshwater crayfish invaders due to its parthenogenetic reproduction combined with early maturation and high fecundity. As their introduced ranges expand, their sympatric populations become more frequent. The question of which species and under what circumstances will dominate in their introduced communities is of great interest to biodiversity conservation as it can offer valuable insights for understanding and prioritization of management efforts. In order to examine which of the aforementioned species may be more successful as an invader, we conducted a set of independent trials evaluating survival, growth, claw injury, and reproduction using single-species stocks (intraspecific interactions) and mixed stocks (interspecific interactions) of marbled crayfish vs. other crayfish invaders since the onset of exogenous feeding. In both single and mixed stocks, red swamp crayfish and yabby grew faster than marbled crayfish, while marbled crayfish were superior to both spiny-cheek and signal crayfish in terms of growth. With the exception of signal crayfish, the faster-growing species consistently reached a higher survival rate. The faster-growing species tended to negatively impair smaller counterparts by greater claw injury, delayed maturation, and reduced fecundity. Only marbled crayfish laid eggs as early as 14 weeks in this study, which is earlier than previously reported in the literature. Thus, the success of marbled crayfish among invasive crayfish is significantly driven by relatively fast growth as well as an early and frequent reproduction. These results shed light on how interactions between invasive populations can unfold when their expansion ranges overlap in the wild, thereby contributing to the knowledge base on the complex population dynamics between existing and emerging invasive species

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Environmental changes such as global warming can affect ecological communities by altering individual life histories and species interactions. Recent studies focusing on the consequences of environmental change on species interactions highlighted the need for a wider, multi-species context including both trophic and non-trophic interactions (e.g. predator interference). However, the effects of biotic and abiotic factors on trophic and non-trophic interactions remain largely unexplored. To fill this gap, we combined laboratory experiments and functional response modelling to investigate how temperature and prey density influence trophic and non-trophic interactions in multiple predator communities. The system under study consisted of predatory dragonfly larvae (Aeshna cyanea) and omnivorous marbled crayfish (Procambarus virginalis) preying on common carp fry (Cyprinus carpio). We estimated the functional response of each predator in single-predator experiments and used this information to disentangle the trophic and non-trophic interactions and their dependence on environmental conditions in multiple predator trials. We found that consumer identity, prey density, and temperature all affect the magnitude of trophic and non-trophic interactions. Non-trophic interactions mostly decreased predator feeding rates, corroborating previous observations that interference prevails in aquatic communities. Moreover, trophic interactions depended primarily on the environmental variables whereas non-trophic interactions depended mainly on consumer identity. Our results indicate that non-trophic interactions among true predators and omnivores can be substantial and that biotic and abiotic conditions further modify the magnitude and direction of these interactions, which can affect food web dynamics and stability.

Nonconsumptive predator-driven mortality (NCM), defined as prey mortality due to predation that does not result in prey consumption, is an underestimated component of predator-prey interactions with possible implications for population dynamics and ecosystem functioning. However, the biotic and abiotic factors influencing this mortality component remain largely unexplored, leaving a gap in our understanding of the impacts of environmental change on ecological communities. We investigated the effects of temperature, prey density, and predator diversity and density on NCM in an aquatic food web module composed of dragonfly larvae (Aeshna cyanea) and marbled crayfish (Procambarus fallax f. virginalis) preying on common carp (Cyprinus carpio) fry. We found that NCM increased with prey density and depended on the functional diversity and density of the predator community. Warming significantly reduced NCM only in the dragonfly larvae but the magnitude depended on dragonfly larvae density. Our results indicate that energy transfer across trophic levels is more efficient due to lower NCM in functionally diverse predator communities, at lower resource densities and at higher temperatures. This suggests that environmental changes such as climate warming and reduced resource availability could increase the efficiency of energy transfer in food webs only if functionally diverse predator communities are conserved.

This study focused on supplementing pikeperch (Sander lucioperca) larvae with rotifers fed with Chlorella vulgaris during the first 15 days post hatching (dph). Larvae were fed a combination of rotifers and artemia under three different enrichments: A) Nannochloropsis occulata, B) Chlorella vulgaris, and C) a commercial enrichment&mdash, Selco, Spresso from INVE. After 17 days from the trial initiation differences were found between treatments on survival rate, myomere height (MH), fatty acid composition, and stress tolerance. In terms of survival, larvae from treatment b (74.5%) and c (66%) excelled over the control (a) treatment (59%). Furthermore, larvae from both the Chlorella (b) and the Selco (c) treatments showed more resilience to stress conditions (10% and 37% reduction in mortality) when exposed to high salinity conditions (18ppt) for 3 h (stress response). Overall, larvae from treatments b and c performed better than those receiving a non-enriched diet (a), likely due to the higher levels of Essential Fatty Acids (EFA) and the ability of pikeperch to desaturate and elongate fatty acids (FA) with 18 carbons to LC PUFAs (Polyunsaturated Fatty Acids). The present study provides valuable input for designing improved feeding protocols, which will increase the efficiency of pikeperch larval culture.

Freshwater biodiversity is globally threatened by various factors while severe weather events like long-term droughts may be substantially devastating. In order to remain in contact with the water or stay in a sufficiently humid environment at drying localities, the ability to withstand desiccation by dwelling in the hyporheic zone, particularly through vertical burrowing is crucial. We assessed the ability of three European native and five non-native crayfish as models to survive and construct vertical burrows in a humid sandy-clayey substrate under a simulated one-week drought. Three native species (Astacus astacus, A. leptodactylus and Austropotamobius torrentium) suffered extensive mortalities. Survival of non-native species was substantially higher while all specimens of Cherax destructor and Procambarus clarkii survived. The native species and Pacifastacus leniusculus exhibited no ability to construct vertical burrows. Procambarus fallax f. virginalis and P. clarkii constructed bigger and deeper burrows than C. destructor and Orconectes limosus. In the context of predicted weather fluctuations, the ability to withstand desiccation through constructing vertical burrows into the hyporheic zone under drought conditions might play a significant role in the success of particular crayfish species, as well as a wide range of further hyporheic-dwelling aquatic organisms in general.