No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Population biology and acid tolerance of the crayfish Cambarus bartonii bartonii (Fabricius) from southern Appalachian Mountain streams were investigated. Field studies were conducted primarily from May through October, 1985 at Coweeta Hydrologic Laboratory (U. S. Forest Service Southeastern Experimental Station) in Otto, North Carolina, to describe selected population parameters and life history events for this species in two first-order streams. Laboratory experiments were conducted using crayfish from Coweeta and from Craig Creek (Jefferson National Forest, Montgomery County, Virginia) to determine median lethal concentrations (LC₅₀) for sulfuric acid exposure, and to investigate physiological effects, influence of ambient water temperature, and effects of episodic acid events on molting. Population estimates of crayfish ranged from 210 to 683 crayfish in 20 to 25m study sections (≃9.2 to 29.8 per m²) of Ball Creek and Pinnacle Branch. Mean catch per baited funnel trap and mean catch per hour of hand collecting were determined in three study sections of each stream in May and September to obtain relative abundance estimates and compare capture methods. Each method selected for different segments (size classes) of the population. Sex ratios were balanced (1:1) over the whole sampling season, but differed significantly from 1:1 in some months, probably due to reproductive activity. Sexually mature males and females (form I males, females with full cement glands) were observed in all months sampled. Acute (96h) laboratory lethality tests yielded LC₅₀ values for pH's of 2.43, 2.56, 2.85 and 2.43 for Coweeta intermolt adults (25.3 to 43.2mm carapace length, CL), late juveniles (11.5 to 19.9mm CL), early juveniles (3.9 to 12.8mm CL) and Craig Creek intermolt adults (23.0 to 41.3mm CL), respectively. Decreased water temperature resulted in increased acid tolerance of intermolt adults (LC₅₀ = pH 2.33), and increased survival time during severe acid exposure. Acid exposure of intermolt adults in relatively soft water affected internal ion regulation, causing decreased hemolymph [Na⁺] and increased [Ca⁺⁺]; no Ca⁺⁺ mobilization (loss) from carapaces was observed. Preliminary work showed that extreme acidification had visible adverse effects on molting adults, causing failure of exoskeletons to become rigid. Episodic acid events at Coweeta do not appear to be a direct mortality problem to C. b. bartonii at this time. However, this does not preclude the possibility of future problems, particularly sublethal effects to reproductive activity or early life history stages, if increasing acidification and gradual loss of soil buffering capacity of watersheds persists. / M.S.

The crayfish plague pathogen, the oomycete Aphanomyces astaci, has been decimating populations of European crayfish species for more than 150 years, and is therefore considered one of the 100 worst world's invasive species. A. astaci is highly specialised for a parasitic life, but it can be isolated from moribund crayfish and grown on synthetic media, as it is the case also for several other oomycetes (chapter 7). The life of A. astaci includes three basic forms: mycelium in host's tissues, and the infective units occurring in water, zoospores and cysts. All North American crayfish species tested so far have shown some resistance to A. astaci, i.e., they could carry the infection for long, serving as vectors of the pathogen. Massive sporulation from infected North American crayfish starts when the host is moulting, stressed, or dying (chapter 4). However, I could show in my experiments that some sporulation occurs even from apparently healthy and non-moulting American crayfish hosting A. astaci, so infected North American crayfish must be considered a permanent source of the infection (chapter 4). Five genotype groups of A. astaci have already been distinguished. Strains from a particular genotype group probably share the same original host crayfish species of North American origin. Nevertheless, they can...

Biological invasions of non-native species are one of the most serious factors threatening global biodiversity. Their negative impacts are particularly evident in the case of freshwater ecosystems and native crayfish populations that live there. Generally, the higher dominance of non-native crayfish species over the native species is relatively well known, but the interactions between non-native crayfish species are significantly less investigated. Although their distribution is increasingly more important and it is obvious that non-native crayfish species will dominate in European waters. However, it is not yet clear which of these crayfish will be more successful. The aim of this diploma thesis was to create a literature review on the topic of interspecific interactions in crayfish with emphasis on native and non-native crayfish species occurring in Europe. The experimental part of the thesis was focused on the comparison of direct interactions and competition for shelter between the widespread spiny-cheek crayfish Faxonius limosus (Rafinesque, 1817) and the newly increasingly occurring marbled crayfish Procambarus virginalis Lyko, 2017. These species are becoming increasingly common in the European wild, but about their mutual direct interactions and competition is largely unknown. During agonistic interactions the marbled crayfish won in significantly more fights than the spiny-cheek crayfish in the absence as well as presence of the shelter. The marbled crayfish established a significantly greater dominance over the females of the spiny-cheek crayfish in the absence and in the presence of shelter, but not over the males. It is also important to say that the presence of the shelter reduces the number of fights and their total duration. There was no significant difference in dominance established by occupation of shelter between the marbled crayfish and the spiny-cheek crayfish. Still, thanks to its aggressiveness, marbled crayfish is able to compete with other non-native species or displace them from freshwater ecosystems.