|
|
Aktivita raka signálního v podmínkách malého toku
DAVID, Jaroslav
The signal crayfish is one of the oldest invasive crayfish species in Europe, causing ecological and often economic damage in newly invaded locations. The invasion and associated problems can be monitored in real-time on the Křesanovský brook, where regular eradication measures have been carried out for six years. However, the detailed and comprehensive impact of these activities on the crayfish population as a whole and any changes in individual behaviour have not yet been studied in detail. To obtain relevant data for this purpose, this thesis video-recorded the situation in the stream in monthly cycles from May to September 2021, with recordings taken the night before and the night after thorough manual crayfish catching in the brook, evaluating the number and activity of observed crayfish. The results did not show that the trapping had changed the overall crayfish activity. Even with a high number of captured crayfish, the weakened crayfish population after trapping showed the same overall activity as the complete population before trapping (presumably due to an increase in individual activity in response to catching and accompanied habitat disturbance). Furthermore, the results underline the previously assumed low success rate of eradication efforts at the site and confirm that barriers in the stream are not sufficient to stop the signal crayfish spread. These findings will help to better understand the impact of eradication measures on signal crayfish populations. As this was the first research of its kind, this thesis opens up opportunities for methodological improvements and further development, as well as posing many new questions that need to be addressed. The ultimate goal of these efforts is to improve management interventions against invasive signal crayfish.
|
|
|
Dynamika společenstva makrozoobentosu podhorského toku s početnou populací raka signálního.
ŠŤASTNÁ, Hana
Assessment of macroinvertebrates population at the Křesanov brook above the town of Vimperk. It contains a large population of the signal crayfish. It is non-native in Europe. Sampling was carried out in 2020. Macroinvertebrates sampling was done. Then, in the laboratory, its determination and detection of abundance and biomass was done. Statistical analyses were subsequently made using hydrobiological indices from the collected data. The analyses compared two stream segments that were different in some parameters.
|
|
|
Effects of diphenhydramine on molecular defense mechanisms in signal crayfish within a bioaccumulation experiment
KAHUDOVÁ, Dominika
Diphenhydramine (DFH) is a medication widely used around the world to treat various types of allergies. Residues of DFH are often detected in surface waters, sediments, and fish tissues. The impact of xenobiotics, such as pharmaceutical residues, on aquatic biota can cause metabolic changes and toxicity in organisms. This study aimed to assess whether DFH affects the molecular defense mechanisms of signal crayfish (Pacifastacus leniusculus) and evaluate the absorption and elimination of the drug in the hemolymph of signal crayfish within a bioaccumulation experiment. Crayfish were exposed to three different concentrations of DFH (2, 20, and 200 ugl-1) for 96 hours. After the experiment, the concentration of DFH in the hemolymph was measured, and crayfish tissue was analyzed. In a second, ten-day experiment, only the concentration of DFH was monitored for absorption and elimination over time at pH values of 6.7 and 8.7. Crayfish were exposed to two concentrations of DFH (20 and 200 ugl-1) for 168 hours and then kept in clean water without DFH for 72 hours. Acute changes in oxidative stress biomarker activity and neurotoxicity biomarkers were observed in the hepatopancreas, gills, and muscles. Environmental and moderately increased concentrations of DFH caused an imbalance only in the activities of enzymes associated with glutathione metabolism. The most significant changes caused by oxidative stress were detected at sublethal concentrations in the muscles. The medication caused changes in the antioxidant defense mechanisms of signal crayfish, but acute neurotoxicity was not detected. The results of the ten-day experiment showed that a greater amount of the pharmaceutical was absorbed at pH close to the dissociation constant of DFH, but no linear dependence of the concentration of DFH in the hemolymph on the size of the crayfish was detected. The data obtained in this study complement the limited knowledge about the effect of DFH on aquatic invertebrates. The results will serve as a methodological basis for further research on the rates of absorption, elimination, and other parameters of bioaccumulation kinetics of pharmaceutically active substances in freshwater crustaceans.
|
|
|
Zhodnocení přežívání a růstu dvou invazivních raků v teplotně suboptimálních podmínkách
MARKOVÁ, Kateřina
Biological invasions of non-native species are one of the most serious threats negatively impairing global biodiversity. The negative influence of these invasions is especially noticeable in freshwater ecosystems also exemplified by the populations of native crayfish species in Europe. Dominance of non-native species of crayfish over native ones is relatively well known and studied, but the interactions between individual non-native invasive species are significantly less explored. As the range expansion and numbers of non-native crayfish species constantly increases, it becomes apparent that the non-native species will dominate in European waters. However, it is not clear which of these invasive species, and under which conditions will perform better. The goal of this bachelor thesis was to create a literature review focusing on factors that negatively influence the population of the native species (mainly the issue of non-native species and crayfish plague which these species often transmit). Consideration was paid to the importance of the water temperature for the crayfish and to the focused species used in the experimental part the marbled crayfish Procambarus virginalis Lyko, 2017 and signal crayfish Pacifastacus leniusculus Dana, 1852. The experiment was focused on the evaluation of survival, growth, damage to the claws, and the maturation of these species at the water temperature of ~16 °C, which is in the optimal range for signal crayfish, but suboptimal for marbled crayfish (yet, within a range presumably allowing its successful reproduction). If these species should meet more frequently in the wild, it is important to understand their relationships.
|
|
|
Proti americkému brouku! Lze odstranit raka signálního z malého toku?
JAKŠ, Jiří
Biological invasion by invasive alien crayfish species is a serious problem for the whole ecosystem. Non-native crayfish species have significantly better biological equipment and ability to adapt to the environment in which they live. This makes them very dangerous animals not only for our native crayfish species. One of these dangerous alien species is the signal crayfish (Pacifastacus leniusculus - Dana, 1852). This species was imported from North America because of economic reasons. At the time of introduction of this non-native species, such massive spreading was not expected as well as negative impacts on native species. Now it is necessary to reduce the number of crayfish and thus significantly help the whole ecosystem. There are several ways how to reduce the population of signal crayfish and other non-native crayfish species. It was the subject of this work and it was only necessary to choose the appropriate method. Finally, one of the least invasive methods was chosen for this work, which is catching crayfish by hand and the net. The Křesánovský brook near Vimperk was chosen as a locality, where is located the dense population of the signal crayfish. This species already significantly reduced all the typical fish species that normally lived in this trout brook, and also significantly reduced the number of native crayfish (Astacus astacus - Linnaeus, 1758). This species can be seen there only rarely and often of a poor fitness. At the beginning of presented work, the main question was how successful this catch method would be. According to current theoretical knowledge, the method of catching crayfish by hand with net has a low success rate and it is not possible to remove the crayfish completely from the stream using this method. However, no one has conducted such a study at small accessible stream and it was therefore appropriate to carry out such a study. After intensive catches in the period from April to November, it was found that we are not able to remove or significantly reduce the number of crayfish living in this stream. However, there are several alternatives that can be used. These alternatives can be found in this work.
|
|
|
Koktejl invazivních druhů ve vnitrozemských vodách - ekologická charakteristika, vzájemné působení a následky
ROJE, Sara
This thesis combines four main chapters: 1) a general summary of the current knowledge of the impact of aquatic invasive species in Europe, ecological characteristics, main representatives, their interaction and the consequences of spread; 2-3) two studies addressing mutual species impacts between invaders co-occurring together in the same habitat; and 4) investigating the differences between the behaviour of native and alien fish species. Chapter 1 looks at the theoretical concept and impacts of aquatic invasive species and in particular, four chosen groups of invaders with a review on specifically chosen high-profile aquatic invasive species in freshwaters, their associated impacts and detailed descriptions of the species used in experiments. Chapter 2 focuses on the predatory impact of killer shrimp on the early developmental stages of marbled and signal crayfish, concluding that killer shrimp are almost unstoppable. They were able to feed on different developmental stages of larger freshwater crustaceans even if they were protected by their mothers. Chapter 3 observes the interactions of two invaders: the round goby and the marbled crayfish. The round goby showed dominant aggressiveness consuming all the juvenile crayfish sizes offered. The study also confirmed that the round goby was able to predate on, attack and take shelters from crayfishes. The only limiting factor in this interaction was the larger size of the crayfish. When interacting, both tested species negatively influenced each other, which can mean mutual consequences for both species. In Chapter 4, the individual behaviour during day and night activity under laboratory conditions in a flow simulator was studied. Both species showed very similar behaviour, with only slight differences towards adaptability and stress-related activity. Despite the similarities, the round goby was confirmed to be an aggressive, bottom-dwelling predator sharing a habitat with a lot of other benthic animals like amphipods, crayfish, and other fish - native or other aliens. In general, all alien species are present a threat to all populations sharing similar characteristics in their habitat, taking their shelters, attacking them, and predating on them with invasive amphipods and crayfish being no exception. One species can limit the other, or the outcompeted species can be displaced forcing it to find an alternative niche and therefore increase the overall pressure on the ecosystem. The presented thesis is submitting some new findings mainly about the interactions between invaders and also represents a baseline for future experimental work focused on more complex setups that will enable us to increase our understanding of invasive species.
|
|
|
Vyhodnocení plodnosti raka signálního včetně post-ovulačního stavu vaječníků
FOJT, Martin
The theoretical part of diploma thesis is aimed at breeding, growth and molting events in crayfish. Thesis is also aimed at life cycle and reproduction of three indigenous crayfish species (Astacus astacus, Austropotamobius torrentium, Pontastacus leptodactylus) and two introduced crayfish species (Faxonius limosus, Pacifastacus leniusculus). The results show apparent linear dependence between female size (POCL), abdomen surface (1M: y = -1061,2 + 65,4*x; r2 = 0,9829; p10-5; 2M: y = -1160,4 + 68,7*x; r2 = 0,8732; p < 10-5) and fertility (1M: y = -194,4 + 12,8*x; r2 = 0,4104 p = 0,0042; y = -330.9 + 15,9*x; r2 = 0.4372; p < 10-4) in once (1M) and twice (2M) molted females. As the length of carapax increase, the area of the abdomen increase and fertility increase in both groups of females. Furthermore, the differences in fertility, carapax length, abdomen surface, and weights in once and twice molted females of signal crayfish. In group of once molted females fertility (t-test, t = -3.12, p = 0.003), carapax length (t-test, t = -3.17, p = 0.003) = -3.24; p = 0.002) and the weight (t-test, t = -3.35; p = 0.002) was higher than in twice molted group of female. Consequentially evaluation of egg size of females. The size of the eggs did not differ between groups of females (1M and 2M) (t-test, t = -0.975, p = 0.335). The mean egg size for both groups of females was 2.71 ? 0.18 mm. Evaluation of post-ovulation conditions of the ovary, including visible signs of females that resorbed unovulated oocytes. Evaluating how much unovulated oocytes were found in the ovaries. Only in 46.4% of the total number of females were ovaries completely empty. In once and twice molted females were found in average 2.2 ? 3.8 and 1.9 ? 2.6. unovulated oocytes, respectively. In once molted, three females didn't lay eggs, two females lost the clutch of eggs. In twice molted females, six females did not lay the eggs and four females lost the clutch.
|
|
|
Interaction of non-native species of crustaceans in Czech waters: Predator or prey?
ŠVAGROVÁ, Kateřina
This diploma thesis deals with non-native species of crustaceans, which are already present not only in Europe but also successfully inhabit the territory of the Czech Republic. The species that this work deals with is the signal crayfish (Pacifastacus leniusculus), marbled crayfish (Procambarus fallax f. virginalis) and the killer shrimp (Dikerogammarus villosus). The main goal of this study was to demonstrate the ability of killer shrimp to attack and prey on the crayfish eggs and hatchlings of above mentioned species, which were used not only for theuir presencein Czech Republic but also as model representatives of families Astacidae and Cambaridae. It was therefore the confirmation of high aggressiveness of killer shrimp and point out, that this species is capable of negatively influencing even the bigger invertebrates by direct predation on their early developmental stages. Another aim was to assess whether the killer shrimp can be a suitable prey for a crayfish. As the experiments have shown, killer shrimp is able to predate on crayfish eggs and hatchlings even directly on females abdomens wehre they are incubated and protected. The results confirmed the theory of killer shrimp hazards to aquatic ecosystems and its potential to directly influence the populations of larger organisms. At the same time, it has been found that killer shrimp may be a suitable prey for adult and subadult individuals of signal crayfish and adults of marbled crayfish.
|
|
|
Reciprocal predation between non-native crayfish and salmonids Who eats whom?
MÜLLEROVÁ, Lucie
Signal crayfish (Pacifastacus leniusculus) is important invasive species in European freshwaters. Its influence on other freshwater organisms is well known from the literature, as well as direct and indirect impact on fish assemblages. This work was focused on the experimental evaluation of non-indigenous signal crayfish as a predator of salmonids compared to indigenous noble crayfish (Astacus astacus). Moreover, the possible importance of young-of-the-year signal crayfish as a prey for salmonids was assessed. There were carried out experiments using eggs and hatchings of grayling (Thymallus thymallus) as a prey for adult and subadult specimens of both, signal and noble crayfish. Next experiment used young-of-the-year signal crayfish as a prey for young-of-the-year of brown trout (Salmo trutta). Results showed that the danger of signal crayfish for grayling eggs is slightly higher. However, detected differences were surprisingly lower and in the majority of parameters even insignificant. In the case of grayling hatchings, was not detected any significant difference at all. The abilities of both tested species to prey on eggs and hatchings are therefore very similar, comparable. Even so, the effect of signal crayfish can be importantly higher in natural conditions because of its more dense populations, higher growth rate and fast maturation. In accordance to our findings, it is evident that brown trout has no so high effect of crayfish juveniles compared with crayfish effect on salmonids early developmental stages. Crayfish are therefore more likely able to limit salmonids than conversely.
|
|
|
Biology and invasive spreading of signal crayfish (Pacifastacus leniusculus) in the Vysočina Region
JUREK, Lukáš
This thesis deals with the issue of non-native crayfish species in Europe, focusing mainly on the Czech Republic. The main species of interest was the signal crayfish. Its biology in relation to invasive spreading was evaluated. The most recent list of its known populations in the Czech Republic was compiled. These data were subsequently compared, updated and enriched with new locations based on this field monitoring. Its occurrence was evaluated largely in the Vysočina Region, in the area of Velké Meziříčí. As it turned out, the center of the signal crayfish occurrence in the Czech Republic is located really in the area of its original introduction thirty years ago in our country, in the vicinity of the Velké Meziříčí. During that time, signal crayfish have successfully expanded into the surroundings waters, both naturaly (downstream and upstream migration) and with human aid (with restocking fish, direct distribution by the public). It occupied all possible types of habitats, from running waters of the two major rivers Balinka and Oslava to their tributaries creeks of different size and character. It found suitable living conditions also in some ponds, particularly those less intensively farmed. Signal crayfish was recorded in areas, where noble crayfish Astacus astacus is still relativelly widely present, in some place even forming sympatric populations. The work was also focused on epibionts Branchiobdella sp., their presence or absence on caught crayfish. Their occurance was also recorded and evaluated.
|
guest ::
