Autecology of Limnomysis benedeni Czerniavsky, 1882 (Crustacea: Mysida) in Lake Constance, Southwestern Germany

AbstractThe Ponto-Caspian mysid Limnomysis benedeni was first recorded in Lake Constance in summer 2006, and a stable population developed at the site of discovery. Although this mysid is common in the Rhine and Danube rivers, little is known about its ecology and impact in systems of invasion. We investigated the autecology of L. benedeni in habitat-choice and food experiments. In the habitat-choice experiments, highly structured habitats, i.e., stones covered with zebra mussels (Dreissena polymorpha), macrophytes, and especially stonewort, were strongly preferred. In food experiments, L. benedeni fed mostly on food sources with a small particle size, e.g., biofilm on leaf litter, biodeposited material of zebra mussels, epilithon, and phytoplankton. We also compared the L. benedeni population data from Lake Constance with that from rivers. In Lake Constance, female L. benedeni were nearly 30% larger and carried more than three times more eggs in spring (9.4±0.6mm and 28.4±5.7 eggs) than in summer (6.7±0.8mm and 8.7±2.9 eggs). The mysids present in spring might be the generation that over-wintered; in summer, this generation was probably replaced by a new generation of smaller individuals. The large brood size and the detritivorous feeding strategy might allow L. benedeni to colonize Lake Constance rapidly

A review of spatio-temporal patterns of the colonisation of Lake Constance with alien Macrozoobenthos

Seit 1958 sind 14 Neozoen des Makrozoobenthos im Litoral des Bodensees nachgewiesen worden. Ein Großteil davon sind Mollusca und Malacostraca (Crustacea) und ihr Haupt-Herkunftsgebiet ist die Pontocaspis. Auffällig ist, dass sich der Schwerpunkt der Erstfunde früher im Untersee befand, seit 10 Jahren jedoch in die Bregenzer Bucht verlagert hat. Im Bericht werden die Arten nach Herkunft und Zugehörigkeit aufgeteilt, ihr Erstfundort im Bodensee und mögliche Einschleppvektoren besprochen und ihre bisher bekannten Folgen auf das Ökosystem des Bodensees dargestell

Life-cycle and population ecology of the freshwater mysid Limnomysis benedeni

The numbers of alien species in freshwater systems and their detrimental impacts on the stability of ecosystems and global species diversity are increasing. The introduction of alien species leads to changes in species composition inter alia. Functional traits of the biota thereby also change, which in turn will likely alter ecosystem processes, e.g. by modifying the availability, capture, and use of nutrients or by affecting the feeding relationships (trophic structure) within a community. To predict and assess such impacts, a thorough knowledge of the autecology and life cycle of the alien species is required. The mysid Limnomysis benedeni, one of the most important ponto-caspian invaders, was found in Lake Constance (southern Germany) in 2006. Since 1958, 14 alien species of the makrozoobenthos have invaded the littoral of Lake Constance. About 1/3 of the species belong to the Peracarida (including Amphipoda, Isopoda and Mysida), 1/3 to the Mollusca (Gastropoda and Bivalvia) and the last 1/3 to other groups of the makrozoobenthos. The main part of the alien species originated in the ponto-caspian region and it is remarkable that formerly, their first records were mainly made in the Upper Lake Constance, but since 10 years has shifted to bay of Bregenz.The aim of the study was to gain knowledge on the possible impacts of L. benedeni on the littoral of Lake Constance. L. benedeni was not a well examined species, so basic studies on the autecology were necessary first. Studies on the life-cycle strategies over an entire seasonal cycle, addressing factors (predation, temperature) which we expected to be most important triggers of the observed changes, indicated that the size class distribution and the reproductive pattern of L. benedeni changes seasonally. During winter (November to March), the mysid invested energy in growth and delayed reproduction until April, when the population was dominated by adults. In summer (June to September), the adults reproduced at a smaller body size and the population was disproportionately dominated by juveniles. In a mesocosm experiment that excluded fish predators, the mysids followed the same seasonal patterns of growth and energy investment as in the field population, but the size class distribution differed. Even in summer, the population in the mesocosm was dominated by adults. Stomach analyses of fish showed that L. benedeni is preyed upon by juvenile Perca fluviatilis in summer, which fed size selectively on larger mysids. Because of the smaller size at maturity, we state that the adults in summer really showed a physiological adaption on the season, perhaps evolved to avoid predation or as a reaction on metabolic losses at higher temperatures, but the shifted length distribution was probably caused by the high fish predation.L. benedeni shows a distinct dependency of the development time of the brood on water temperature. In laboratory experiments under controlled conditions, we determined embryonic development times and the probability of survival of the females and juveniles at water temperatures ranging from 4° to 25° C. At 6.5° and 25° C, the probability of survival of both the females and the larvae was lower than at 10°, 15°, or 20° C. With the determined equation for the development time as a function of water temperature, it was now possible to estimate population rates, e.g. birth and mortality rates. Direct field measurements of the main population characteristics (abundance, biomass, clutch size, sex ratio) were combined with general ecological equations developed for species with other ecological behaviours. L. benedeni reproduces continuously instead of producing cohorts, with high, fluctuating abundances. We estimated instantaneous mortality rates of L. benedeni in the littoral by calculating instantaneous birth population growth rates. The formulae used served well for the estimations. During the reproduction period in summer, the instantaneous mortality rate was high, but the instantaneous birth rate was high enough to balance the population growth rate. The instantaneous mortality rates reinforced the known life-cycle patterns of L. benedeni and confirmed the assumption that the life-cycle shift in summer is an adaption to high predation on the population by fish.The feeding mode and food preference of adult L. benedeni collected from the field and from laboratory feeding experiments were examined by analysing their stomach contents. In a second setup with two sets of laboratory growth experiments, we determined the growth of juveniles by feeding newly hatched juveniles with different natural food sources at different water temperatures. The stomach analyses showed clearly that L. benedeni fed non-selective on organic particles smaller than ~ 200 µm both by filtering or grazing. They fed well on biofilm in the field as well as in laboratory growth experiments and we suppose a high disturbance potential of the mysid on the biofilm community. As a reason of their feeding mode, we conclude that L. benedeni has no predatory impact on zooplankton in the field and probably affects nutrient cycles in the littoral. L. benedeni seams to be a good food source for perch, but will not cause a massive decline of the fish community as it is describes from other mysids. However, the effect on the perch growing, if there is any, will be small in both ways, negative or positive. Perhaps the perch will profit from the new food source, but it could be that the effect will be negated because L. benedeni only replaces other prey species.With this study, we contribute a huge step in understanding freshwater mysid ecology, life-cycle physiology and population dynamics. In sum, L. benedeni has the potential to play an important role in the trophic relations in the littoral, via “bottom-up” mechanisms as well as via “top-down” control, and will persist an important invasive species in Europe

Katamysis warpachowskyi Sars, 1877 (Crustacea, Mysida) invaded Lake Constance

The mysid Katamysis warpachowskyi Sars, 1877 originated in the Ponto-Caspian region and the associated river systems. The first evidence of its transgression of the limits of the watersheds of its natural Ponto-Caspian origin was found when three individuals were recorded in October 2009 in eastern Lake Constance (Austria). In March 2010, K. warpachowskyi comprised 10% of the mysid assemblage and was mainly found in rocky habitats. On both sampling dates, breeding females were present. Before this invasion, Limnomysis benedeni Czerniavsky, 1882, was the only mysid in Lake Constance and is also distributed in the Rhine river system. Since the two mysids coexist in Lake Constance, K. warpachowskyi will likely become established in the lake and further expand into the main part of the Rhine. K. warpachowskyi is known as a benthic organism and feeds on detritus and small algae; therefore, the impact on the lake ecosystem should be weaker than that of pelagic mysids

First record of Crangonyx pseudogracilis Bousfield 1958 (Amphipoda, Crustacea) in Lake Constance

Crangonyx pseudogracilis wurde im November 2007 bei Hard in der Nähe von Bregenz zum ersten Mal im Bodensee nachgewiesen. Dies ist zugleich auch der Erstnachweis für Österreich. Im Dezember wurde die Art bei weiteren Probenahmen an derselben Stelle sowie bei der gezielten Nachsuche in der nahegelegenen in den Bodensee mündenden Dornbirner Ach gefunden. Die Fundumstände werden vorgestellt und der mögliche Einfluss der Art auf die Artengemeinschaften des Bodensees diskutiert

Embryonic development time of the freshwater mysid Limnomysis benedeni Czerniavsky as a function of water temperature

The numbers of alien species in freshwater systems and their detrimental impacts on the stability of ecosystems and global species diversity are increasing. To predict and assess such impacts, a thorough knowledge of the autecology and life cycle of the alien species is required. Limnomysis benedeni is common and one of the most invasive mysids in Europe. Here we show a clear dependency of the development time of the brood of L. benedeni on water temperature. In laboratory experiments (one in spring 2008 and two in 2009, in spring and summer) under controlled conditions, we determined embryonic development times and the probability of survival of the females and juveniles at water temperatures ranging from 4 to 25_C. At 6.5 and 25_C, the probability of survival of both the females and the larvae was lower than at 10, 15, or 20_C. Since the development time is one of the key characteristics of the life cycle and is therefore necessary to calculate, for example, birth and mortality rates, we determined an equation for the development time as a function of the water temperature. This information will be useful to understand the distribution potential of this invasive species

Seasonal shifts in the life cycle of the ponto-caspian invader Limnomysis benedeni (Crustacea: Mysida) : a physiological adaptation?

The mysid Limnomysis benedeni, one of the most important ponto-caspian invaders, was found in Lake Constance (southern Germany) in 2006. As part of larger studies to evaluate the effects of L. benedeni on the ecosystem, we studied its life-cycle strategies over an entire seasonal cycle in intervals of 3–5 weeks, addressing factors (predation, temperature) which we expected to be most important triggers of the observed changes. The size class distribution and the reproductive pattern indicated that the life cycle of L. benedeni changes seasonally. During winter (November to March), the mysid invested energy in growth and delayed reproduction until April, when the population was dominated by adults. In summer (June to September), the adults reproduced at a smaller body size and the population was disproportionately dominated by juveniles. In a mesocosm experiment that excluded fish predators, the mysids followed the same seasonal patterns of growth and energy investment as in the field population, but the size class distribution differed. Even in summer, the population in the mesocosmwas dominated by adults. Stomach analyses of fish showed that L. benedeni is preyed upon by juvenile Perca fluviatilis, which fed size selectively on larger mysids. In conclusion, our results suggest predation was the reason for the dominance of juveniles and the observed size class distribution in summer. In contrast, the smaller adults in summer were most likely a physiological adaptation, perhaps evolved to avoid predation or as a reaction on metabolic losses at higher temperatures

Niche differentiation between sympatric alien aquatic crustaceans : An isotopic evidence

Among the mechanisms that allow competing species to coexist are resource partitioning and dietary segregation. The current study uses multiple stable isotopes, carbon ( 13C), nitrogen ( 15N) and sulphur ( 34S), to test the hypothesis that dietary segregation in cohabiting invasive mysids (Limnomysis benedeni and Katamysis warpachowskyi) and gammarids (Dikerogammarus villosus and Gammarus roeselii) will be reflected by differences in isotope values. Furthermore, IsoError mixing models were used to estimate the relative contributions of periphyton and seston to the invaders’ diets. Whole tissue 13C, 15N and 34S analysis in L. benedeni and K. warpachowskyi imply that these sympatric, non-native mysids maintain differentiated feeding niches or resource partitioning by feeding on distinct components of the available food resources (predominantly seston by L. benedeni and periphyton by K. warpachowskyi). By contrast, the gammarids D. villosus (‘killer shrimp’) and G. roeselii exhibited no significant difference in 13C and 15N, indicating a considerable overlap between the dietary sources of these sympatric invaders. Feeding niche differentiation, irrespective of season or the nature of habitat invaded (lake or river), might facilitate the coexistence of invasive mysids in their ‘new’ environment by minimizing direct resource competition. The mutual interaction by the invasive gammarids, coupled with voracious behavior, could assist their success at co-invasion with serious implications for local biodiversity including the potential extinction of native species