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Langenargen, Germany

Marmorkrebs are one of 12 currently known non-indigenous crayfish species (NICS) to be found in Central European waters. It is unique in the manner that there exist only females which reproduce parthenogenetically, i.e. eggs develop unfertilized and all offspring are genetically identical. Marmorkrebs have been first discovered in the German aquarium trade in the mid 1990s and became a very common pet species since then. Here, we present first evidence for a well established Marmorkrebs population in a small lake in the Upper Rhine catchment near Freiburg (Germany). The population occurs syntopically with Orconectes limosus, another NICS which invaded the Rhine system about 50 years ago. Morphometric and ovary weight measurements were taken from 12 Marmorkrebs specimens that were captured on July 3, 2010. The rostrum spination was pronounced and resembled the one found on a free-living individual captured in Saxony (Germany). Ovary development stages (Gonadosomatic Index) were heterogeneous and single berried females were found from early June to late July, which might indicate an asynchronous breeding habit. The relative abundance and distribution of both crayfish species were assessed by visual counts at nighttime at two occasions. Both species attained a comparable, moderate density throughout the lake margin. The Marmorkrebs was the prevalent species on shallow, swampy habitat patches, which are presumably similar to its natural prime habitats. The successful establishment of Marmorkrebs despite a pre-existing O. limosus population, stresses the competitive ability of Marmorkrebs. In addition to the recently suggested hypothesis that Marmorkrebs might be temperature limited in most parts of Europe, we feel that it is also necessary to consider its probable natural prime habitats and life cycle: Marmorkrebs are presumably able to colonize summer-warm, lentic habitats in most parts of Central Europe. © 2010 The Author(s). Source

Chucholl C.,University of Ulm | Chucholl C.,Fisheries Research Station BW
Biological Invasions | Year: 2013

The trade of live ornamental freshwater crayfish has grown rapidly in the last decade and has become the major pathway for new non-indigenous crayfish species (NICS) introductions into Europe. Here, I report on the German ornamental crayfish trade, the main importer of non-indigenous crayfish into Europe. In total, 120 NICS have been available as ornamental aquarium species. One hundred and five species originate from North or Central America and are, therefore, suspected to be crayfish plague vectors. The import rate since 2005 was estimated to be seven new species per year. Despite many species being imported, only eleven species were found to be very common in the trade. In 2009, 16 online shops offered at least 37 NICS. The availability, price, and size of the offered species were used to predict their introduction status. Multiple binary logistic regression analysis showed that species' availability and size were the principal predictors of the likelihood of being recorded as introduced from aquaria. NICS introduced from aquaria were found to be more available and larger than those present only in aquaria, and their potential invasiveness was also higher. The findings are consistent with the propagule pressure hypothesis in that a greater availability is likely related to more release events, and large species may be released more frequently as a result of overpopulating or outgrowing their aquaria. Efforts to mitigate the risk of further harmful crayfish introductions from aquaria should aim to drastically reduce the availability of high-risk species. © 2012 Springer Science+Business Media B.V. Source

Chucholl C.,University of Ulm | Chucholl C.,Fisheries Research Station BW
Knowledge and Management of Aquatic Ecosystems | Year: 2012

In the present study, the life history and diet of the highly successful North American invader Orconectes immunis was assessed for the first time in its introduced European range. In 2007, O. immunis population dynamics were monitored in a typical backwater habitat using unbaited funnel traps, and its life history was analysed using Von Bertalanffy's growth function. Juveniles hatched as early as March and may attain sexual maturity at the end of their first summer. The adult population moulted up to four times during the summer months, with the non-breeding form (II) lasting for a remarkably short time period. The high growth rate of O. immunis was combined with a short longevity, which was estimated at 2.5 years. The fecundity ranged from 119 to 495 pleopodal eggs. The stomach contents were dominated by detritus, followed by macroinvertebrates and macrophytes, and no ontogenetic shift in diet was observed. The ability to prey on a wide array of invertebrate taxa presumably supports the sustained high growth rate of O. immunis. The presented data provide evidence that O. immunis exhibits a strongly r-selected life history and omnivorous feeding habits. These ecological properties have often been linked to successful invaders and enhance the invasiveness of O. immunis. © 2012 ONEMA. Source

Procambarus clarkii is one of the worst invasive and best-studied crayfish species worldwide, but its life history at higher latitudes is poorly understood. In the present study, the population ecology of P. clarkii was studied for the first time within its northeastern range limit in Europe (southern Germany) for a two-year period, and the findings are used to discuss several life-history parameters across different latitudes of its current distribution range. The reproductive cycle was tracked using the gonadosomatic index and reproductive traits in females and the reproductive form in males. Life-history parameters were estimated using Von Bertalanffy's growth function. Reproduction was univoltine and occurred from late summer to autumn. A small proportion of females carried eggs throughout the winter. This contrasts with the species' multi-voltine life cycle at lower latitudes, with year-round breeding and several reproduction peaks per year. Growth was estimated to be slower than at lower latitudes, whereas longevity, mean lifetime and size increased. These changes in life history probably reflect a general phenomenon at higher latitudes and, thus, latitudinal clines. The presented findings provide evidence that P. clarkii is able to cope well with new cold habitats by modulating its life history. © 2011 ONEMA. Source

Chucholl C.,University of Ulm | Chucholl C.,Fisheries Research Station BW
Aquatic Invasions | Year: 2011

Procambarus clarkii is among the worst invasive species that have invaded Europe. It originates from the central south of the USA and northeastern Mexico and is a hardy, r-selected generalist. There exists a marked gradient in population numbers from southwestern to northeastern Europe: The Iberian Peninsula, Italy and France have the bulk of the populations, while northeastern populations are mainly scattered and isolated from each other. In the present study I report on the distribution of P. clarkii in an artificial lake system along the River Danube in Southwestern Germany, which is within its northeastern range limit. The presence of P. clarkii was confirmed in nine lakes and one canal with stagnant water. Procambarus clarkii was absent from lotic situations, which may indicate that P. clarkii thrives chiefly in stagnant or slow flowing waters. A probable explanation is that those habitats heat up faster and reach higher summer temperatures than most lotic habitats. Since P. clarkii is considered as a ́warm water ́ species, lentic habitats probably offer more favorable temperatures. The populations form two disjunct distribution centres, isolated from each other by around seven km linear distance. It is not known for sure when the species was initially introduced, but it may have been present in the western distribution centre since the mid 1970s. The emerging disjunct distribution pattern is a synergistic result of introductions into two lakes and subsequent active spread to surrounding habitats, including migration overland. Procambarus clarkii numbers are often high and the species has become a nuisance to recreational fishery, since it tends to grab on to exposed fish bait. Two noble crayfish (Astacus astacus) populations were wiped out rapidly by P. clarkii, presumably due to crayfish plague transmission. Although eradication may prove impossible, population management, e.g. intense trapping and stocking of predatory fish, is strongly suggested. Early eradication, if necessary relying on extreme control methods (e.g. chemical agents), should be attempted when P. clarkii invades further lakes. © 2011 The Author(s). Source

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