Distribution patterns and predation risk of the coexisting cladocerans Bythotrephes longimanus and Leptodora kindtii in a large lake – Lake Constance

The distributions of the coexisting, planktonic, predatory cladocerans Bythotrephes longimanus and Leptodora kindtii were studied at four different stations (Langenargen-Arbon, Fischbach-Uttwil, Bregenzer Bucht and Zeller See) of a great lake, Lake Constance. The stations Langenargen-Arbon and Fischbach-Uttwil are deep (>200 m) with a high density of the coregonid fish Coregonus lavaretus, the stations Bregenzer Bucht and Zeller See are shallow (<60 m) with lower densities of coregonid fish. B. longimanus was present in the pelagic zone from mid May to November at all stations. L. kindtii generally appeared slightly later in the year than B. longimanus. Peak abundances of B. longimanus with more than 5000 ind. m^–2 (Langenargen-Arbon) appeared in late spring. During summer, when predation pressure by fish is high, abundance of B. longimanus decreased gradually. In contrast, L. kindtii displayed maximum abundances with more than 18 000 ind. m^–2 (Zeller See) in summer. During the summer months, B. longimanus lived in greater depths than L. kindtii. Differences of vertical distribution between both species were most pronounced at the deep stations (Langenargen-Arbon, Fischbach-Uttwil). Analysis of stomachs of the planktivorous fish Coregonus lavaretus showed that B. longimanus was preferred by C. lavaretus over all other prey; Ivlev's selectivity index was 0.97–0.99. Due to this high positive selection for B. longimanus by coregonids, it is surprising that the cladoceran could maintain its existence since the first recordings in 1877. Spatial refuge or indigestible resting eggs may be the underlying mechanism for this phenomenon.     

Impact of Bythotrephes longimanus on zooplankton assemblages of Harp Lake, Canada: an assessment based on predator consumption and prey production

1. Following the 1993 invasion of Harp Lake by Bythotrephes longimanus a number of small-bodied zooplankton declined dramatically compared to pre-invasion densities, and some larger species increased. 2. To test whether these changes were caused by Bythotrephes, we measured its consumption of zooplankton in 1995 and compared this to production by the prey species with which it overlapped spatially and temporally. 3. On a seasonal basis Bythotrephes consumption was 199 mg dry mass (DM) m⁻², or 25% of zooplankton production which was 783 mg DW m⁻². However, for some species, such as the small copepod Tropocyclops extensus , consumption greatly exceeded production—this was one of the species noted to decline in Harp Lake following the appearance of Bythotrephes . By contrast, for the larger cladocerans Daphnia galeata mendotae and Holopedium gibberum , consumption was much less than production—these species were observed to increase following the invasion. 4. Our results thus support the hypothesis that zooplankton changes in Harp Lake were caused by Bythotrephes . We speculate that lower quality prey remaining in Harp Lake may lead to reduced densities of Bythotrephes , or impose strong selective forces that lead to new adaptations by this predator.     

Investigations on fecundity of Bythotrephes longimanus in Lake Lucerne (Switzerland) and on Niche Segregation of Leptodora kindti and Bythotrephes longimanus in Swiss lakes

In Lake Lucerne, Switzerland, the predaceous cladocerans Leptodora kindti and Bythotrephes longimanus segregate along spatial and temporal dimensions. In spring (April–May/June), Bythotrephes longimanus occurs below 0–20 m, while Leptodora is absent. In summer and early autumn (July–September/October), when Leptodora dominates during daytime in the 0–20 m depth, Bythotrephes longimanus also lives in deeper zones. Food competition and fish predation pressure may be the cause of differences in ecology of Leptodora and Bythotrephes acquired during evolution. Due to its transparency and tolerance of higher temperature, Leptodora could avoid fish predation and, therefore, competes with Bythotrephes longimanus successfully. In addition, the differences between the two species may account for the spatial and temporal niche segregation in oligotrophic Swiss Lakes. But spatial niche segregation is less important in mesotrophic lakes with high prey density than in oligotrophic lakes with low prey density. In small, eutrophic lakes importance of temporal niche segregation also decreases, and Bythotrephes is seldom or not present. The preference of Bythotrephes to live in deeper water to avoid fish predation during summer may be the cause of its difficulties to establish itself in small and eutrophic lakes with high prey densities, where the hypolimnion is missing or anoxic.In the spring, Bythotrephes exhibits r-strategy (smaller body size and a higher fecundity), the female is already fertile after the first molt. In the summer, a K-strategy prevails (larger body length and lower fecundity than in the spring), and female Bythotrephes are fertile only after the second molt. Shortage of prey (biomass of Bosmina and Daphniadecreased after June especially in the surface layers) and the maximum fish predation pressure in summer may change the life strategy of Bythotrephes: while fecundity decreases from generation to generation, body length increases. Enhanced prey densities (e.g. during mesotrophic conditions in L. Lucerne) lead to larger individuals in summer and autumn.     

Modification of the diel vertical migration of Bythotrephes longimanus by the cold-water planktivore, Coregonus artedi

1. The weak diel vertical migration observed in the large cladoceran Bythotrephes longimanus seems contradictory to the predator‐avoidance hypothesis that predicts large zooplankton should have long migration amplitudes. However, cold‐water planktivores, especially Coregonus spp., are a main source of mortality for Bythotrephes and hence a deeper migration would result in a greater overlap with these hypolimnetic planktivores. We hypothesized that Coregonus artedi (cisco) modifies the normal vertical migration pattern of Bythotrephes, such that the latter stays higher in the water column during the day and thus migrates less extremely at night. 2. The vertical distribution of Bythotrephes during the day was determined from single visits to six lakes in Ontario, Canada, all of which contain warm‐water, epilimnetic planktivores but differing in whether they contain cisco. One lake of each fish type was sampled day and night every 2–3 weeks over the ice‐free season to examine daytime depths and migration amplitude. 3. The vertical migration of Bythotrephes differed in the presence and absence of cisco. In the lakes with cisco, there were significantly fewer Bythotrephes in the hypolimnion and they were higher in the water column during the day. Migration amplitude was smaller in the cisco than in the non‐cisco lake. These observations were not attributable to differences in physical factors, and, although not conclusively attributable to cisco, are consistent with an effect of cisco. 4. We suggest that diurnal depth selection by Bythotrephes in lakes containing cisco is a trade‐off between the risk of predation by warm‐ versus cold‐water predators, balanced by the benefits of increased temperature and feeding rates near the surface. Even in lakes without cisco, however, the vertical migration of Bythotrephes was less than expected, suggesting that diurnal depth selection is a balance between the risk from warm‐water planktivores and access to sufficient light to feed effectively.     

Bythotrephes longimanus in the Commonwealth of Independent States: variability, distribution and ecolog

Bythotrephes is presently extending its distribution to basins throughout Europe and North America. We used long term data (1880–1997) on Bythotrephes longimanus in Eurasian waterbodies to characterize its ecology and tolerance to different ecological factors. Depending on season and environmental conditions of the waterbody, Eurasian B. longimanus may undergo cyclomorphosis and can exist as two distinct forms ( B. longimanus or B. cederstroemi). Regional forms of the species ( B. l. var. balticus, B. l. var. it transcaucasicus, and B. l. var. arcticus) have also been described. Occurrence and density of Bythotrephes populations varies across geographical scales, and are apparently affected primarily by water temperature and salinity. Bythotrephes is limited to regions where water temperature ranges between 4 and 30 ^C, although the species prefers waters between 10 and 24 °C. Bythotrephes tolerates salinity values between 0.04 and 8.0¡, though it prefers water between 0.04 and 0.4¡. These factors strongly restrict Bythotrephes' distribution in warmer and more saline waters of the Commonwealth of Independent States (CIS), particularly in southern Russia and Kazakhstan. Local abundance and distribution of Bythotrephes is affected by abiotic factors, including basin morphometry and flushing rate, temperature, oxygen concentration and pH, as well as by lake trophic status and fish predation. Planktivorous fish may restrict habitat use by Bythotrephes to regions of basins where overlap between these groups is minimized. Rivers, canals, and ephemeral waterbodies serve as important modes of Bythotrephes' dispersal throughout the CIS and western Europe. Morphological adaptations (e.g. a long caudal process, cyclic parthenogenesis, and production of resting eggs) permit Bythotrephes to tolerate seasonally inhospitable conditions, assist in its dispersal and range extension, and minimize fish predation.     

Non-lethal effect of the invasive predator Bythotrephes longimanus on Daphnia mendotae

1. We evaluated the antipredator behaviour of Daphnia mendotae to the invasive invertebrate predator, Bythotrephes longimanus, and the consequent effect of the predator on prey growth rate (referred to as a non‐lethal effect of the predator). 2. In a laboratory experiment, Daphnia in the absence of Bythotrephes kairomones remained in the top, warmer regions of experimental columns, whereas in the presence of Bythotrephes kairomones, Daphnia migrated vertically, occupying a middle region by night and a low, cold region during the day. Over a 4‐day experiment, the vertical migration induced by Bythotrephes caused a 36% reduction in the somatic growth rate of Daphnia, a level that is sufficient to have an effect on prey population growth rate. 3. A second laboratory experiment indicated that concentrations of Bythotrephes kairomones in water taken directly from the field (Lake Michigan) were high enough to induce behavioural shifts that led to these large reductions in somatic growth rate. 4. Our results identify a means by which Bythotrephes has substantial effects on native prey populations other than through direct consumption.     

Influence of light on the foraging impact of an introduced predatory cladoceran,Bythotrephes longimanus

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Contrasting life histories of the predatory cladocerans Leptodora kindtii and Bythotrephes longimanus

The predatory cladocerans, Leptodora kindtii (Focke, 1844) andBythotrephes longimanus (Leydig, 1860), express markedly differentlife-history traits. Leptodora produce small-bodied neonatesthat mature at small sizes but continue to grow throughout life.Bythotrephes produce larger neonates in both relative and absoluteterms that grow rapidly to a large size at maturity whereuponthey curtail somatic growth and divert resources mainly to reproduction.Despite their remarkable differences, the sets of life-historytraits of both species appear to be solutions to the same basicselection pressures imposed by visually discriminating gape-limitedfishes and foraging constraints imposed by prey size. Leptodorastresses pre-contact (transparency) while Bythotrephes stressespostcontact (caudal spine) modes of morphological defense againstfishes. Mounting these disparate modes of defense has consequencesfor selection on timing and allocation to body growth that mayunderlie competitive imbalance between the species. Owing tothe production of large-bodied neonates that grow rapidly, Bythotrephesquickly attain body sizes that both admit them to a broaderprey base in size and taxonomic variety, and allow shorter preyhandling times, in comparison to Leptodora. This provides Bythotrepheswith a wider and more exploitable prey base from an earlierage and may explain why Leptodora has declined in density followingBythotrephes invasion into some North American lakes. The divergentsets of life-history traits expressed by Leptodora and Bythotrephesparallel two dominant life-history strategies evolved by phytoplanktivorousspecies of the order Cladocera.     

Food limitation impacts life history of the predatory cladoceran Bythotrephes longimanus, an invader to North America

North American invasions of the predatory cladoceran Bythotrephes longimanus have resulted in declines in native zooplankton abundance, species richness, and diversity. In the field, population maxima of Bythotrephes are positively correlated to those of their zooplankton prey. To test the hypothesis that increased prey availability enhances Bythotrephes fitness, we reared Bythotrephes in the laboratory on three mixed-species prey densities (equivalent to 15, 30, and 45 prey organisms day^?1; designated “low,” “medium,” and “high” food treatments, respectively) over 22 days at 21°C. Bythotrephes consumed the daily equivalent of 9, 14, and 22 prey organisms at the low, medium, and high food densities. Smaller, slower prey were most often selected. Indeed, with increasing prey density, Bythotrephes’ predation rates increased, resulting in significantly higher population growth rates, net reproductive rates, growth, and first brood clutch and offspring sizes; significantly faster generation times; and shorter maximum life spans. We propose that the positive relationship between Bythotrephes population maxima and prey seen in the field is largely due to increased predation rates by Bythotrephes when prey abundance is high and the fitness benefits that ensue. Our findings may be useful for Bythotrephes risk and impact assessments.     

Reaction distance of Bythotrephes longimanus, encounter rate and index of prey risk for Harp Lake, Ontario

SUMMARY 1. Some predatory zooplankton, such as the large cladoceran Bythotrephes longimanus (Leydig), have a large compound eye, hence vision may play an important role in prey detection and encounter. Our objectives were to quantify, under different light regimes, the reaction distance of Bythotrephes to an assortment of zooplankton prey and to model encounter rate with prey from Harp Lake, Ontario. Reaction distance to prey increased at higher light intensity.
2. Results from the encounter model show that small, slow-moving prey faced the greatest risk from Bythotrephes and most encounters occurred in the upper 10 m of the water column throughout the 24-h period. The model was highly sensitive to ambient light. Encounter rate and prey risk were two to three orders of magnitude more sensitive to swimming velocity of the predator than to that of the prey.     

Life history characteristics and distribution of Bythotrephes longimanus Leydig (Crustacea,Onychopoda) in the Biesbosch reservoirs

The diel and horizontal distributions of Bythotrephes longimanus Leydig, Leptodora kindti (Focke) and Anomopoda (cladocerans), as well as several life history parameters of each developmental stage of B. longimanus were studied in the non-stratified Biesbosch reservoirs. Anomopoda avoided the surface layer during the day only in the pelagic zone. In the surface layer near the shore, however, they were very abundant. Because densities in the pelagic zone during the day were very low, and high during the night, the population undoubtedly moved from the littoral zone or from the sediments to the pelagic. Accumulation of zooplankton at the littoral site is either the result of random dispersal or wind-induced movements. Bythotrephes' diel distribution pattern is possibly related to that of their prey, the anomopods. Leptodora mostly exhibited a normal diel vertical migration with a small amplitude. Wind most likely influenced the horizontal distribution of the zooplankton. Bythotrephes body length increased with higher temperatures, whereas spine length was constant throughout the year. Bythotrephes can already be fertile in the first developmental stage, indicating that a rapid adaptation to a favourable environment is possible. The number of parthenogenetically produced eggs per ovigerous female was higher at the start of the growing season and constant throughout the rest of the year. Relatively few resting eggs and males were found in autumn.     

Changes in the crustacean zooplankton community of Harp Lake, Canada, following invasion by Bythotrephes cederstrœmi

1. Detecting the impacts of invading Bythotrephes cederstrœmi (Crustacea, Onychopoda, Cercopagididae) on zooplankton in North American lakes has been hampered by the brevity of pre-invasion data, and by the difficulty of distinguishing the effects of the invader from other stresses. The data from Harp Lake in Ontario, Canada, circumvent these difficulties. Bythotrephes appeared in the lake in 1993. There is a 15-year pre-invasion data set, and no significant complicating concurrent stresses.
2. The species composition and the size structure of the crustacean zooplankton community of Harp Lake changed after the invasion. Several small species either declined dramatically in abundance (e.g. Bosmina longirostris , Tropocyclops extensus ) or disappeared ( Chydorus sphaericus , Diaphanosoma birgei , Bosmina ( Neobosmina ) tubicen ). In contrast the abundance of the larger cladocerans Holopedium gibberum and Daphnia galeata mendotae and the hypolimnetic copepod Leptodiaptomus sicilis increased. Several univariate and all multivariate summarizations of zooplankton abundance, biomass and size structure highlighted the uniqueness of the post-invasion community.
3. The alterations in the zooplankton community could not be attributed to changes in lake acidity, thermal regimes, penetration by ultraviolet light, nutrient status, fish stocking or the abundances of native invertebrate predators, but they were correlated with Bythotrephes abundance, both within and among years. Hence, we hypothesize that the invasion by Bythotrephes has significantly altered the crustacean zooplankton community of Harp Lake.     

Changes in the crustacean zooplankton community of Harp Lake, Canada, following invasion by Bythotrephes cederstrœmi

1. Detecting the impacts of invading Bythotrephes cederstrœmi (Crustacea, Onychopoda, Cercopagididae) on zooplankton in North American lakes has been hampered by the brevity of pre-invasion data, and by the difficulty of distinguishing the effects of the invader from other stresses. The data from Harp Lake in Ontario, Canada, circumvent these difficulties. Bythotrephes appeared in the lake in 1993. There is a 15-year pre-invasion data set, and no significant complicating concurrent stresses.
2. The species composition and the size structure of the crustacean zooplankton community of Harp Lake changed after the invasion. Several small species either declined dramatically in abundance (e.g. Bosmina longirostris , Tropocyclops extensus ) or disappeared ( Chydorus sphaericus , Diaphanosoma birgei , Bosmina ( Neobosmina ) tubicen ). In contrast the abundance of the larger cladocerans Holopedium gibberum and Daphnia galeata mendotae and the hypolimnetic copepod Leptodiaptomus sicilis increased. Several univariate and all multivariate summarizations of zooplankton abundance, biomass and size structure highlighted the uniqueness of the post-invasion community.
3. The alterations in the zooplankton community could not be attributed to changes in lake acidity, thermal regimes, penetration by ultraviolet light, nutrient status, fish stocking or the abundances of native invertebrate predators, but they were correlated with Bythotrephes abundance, both within and among years. Hence, we hypothesize that the invasion by Bythotrephes has significantly altered the crustacean zooplankton community of Harp Lake.     

Mechanisms regulating zooplankton populations in a high-mountain lake

SUMMARY 1. We studied the seasonal succession of phyto- and zooplankton and the potential impact of predation by salmonids on zooplankton population dynamics in a high-mountain Swiss lake.
2. A comparison of patterns in the abundance, body length, fecundity and age structure in the Daphnia galeata population strongly suggests that trout predation had little impact on the population and was not the cause for a decline in summer.
3. The dominance in the lake of adult trout that feed mainly on benthic prey may buffer the effect of predation on the larger zooplankton. Further, the relatively high amount of phytoplankton after spring thaw could be important for sustaining the Daphnia population under moderate fish predation.
4. Partial correlation analyses proved circumstantial evidence for both exploitative and interference competition between some zooplankton taxa. D. galeata depressed performance of other plankton species through exploitative competition.
5. Our study shows that the impact of fish on zooplankton in high-mountain lakes depends strongly on food web structure and trophic state of the lake. Where fish predation is weak, invertebrate predation combined with competition for food may be responsible for the dominance of large-bodied zooplankton species.     

Shaping up model transferability and generality of species distribution modeling for predicting invasions: implications from a study on Bythotrephes longimanus

When using species distribution models to predict distributions of invasive species, we are faced with the trade-off between model realism, generality, and precision. Models are most applicable to specific conditions on which they are developed, but typically not readily transferred to other situations. To better assist management of biological invasions, it is critical to know how to validate and improve model generality while maintaining good model precision and realism. We examined this issue with Bythotrephes longimanus, to determine the importance of different models and datasets in providing insights into understanding and predicting invasions. We developed models (linear discriminant analysis, multiple logistic regression, random forests, and artificial neural networks) on datasets with different sample sizes (315 or 179 lakes) and predictor information (environmental with or without fish data), and evaluated them by cross-validation and several independent datasets. In cross-validation, models developed on 315-lake environmental dataset performed better than those developed on 179-lake environmental and fish dataset. The advantage of a larger dataset disappeared when models were tested on independent datasets. Predictions of the models were more diverse when developed on environmental conditions alone, whereas they were more consistent when including fish (especially diversity) data. Random forests had relatively good and more stable performance than the other approaches when tested on independent datasets. Given the improvement of model transferability in this study by including relevant species occurrence or diversity index, incorporating biotic information in addition to environmental predictors, may help develop more reliable models with better realism, generality, and precision.     

Diel patterns of zooplankton grazing in a shallow lake

A diel survey of in situ species-specific zooplankton clearancerates (with radioactively labelled Chlorella cells) was conductedin the shallow lake of Cr?teil characterized by small-sizedplanktonic forms (algae<10µm and zooplankton <1.3mm). Experiments were performed every 4h at two depths (1 and4m). Power functions relating individual filtering rates tobody length were established for the three most abundant cladoceransand for calanoids (nauplii being included in this feeding group),for each depth and time. No filtering penodicity was observedin Ceriodaphnia spp., adults and copepodites of Eudiaptomusgracilis and Eurytemora velox, and nauplii. On the contrary,clear nocturnal filtering peaks were obtained for Daphnia spp.and for Diaphanosoma brachyurum, these being more pronouncedfor the larger individuals at 1 m deep. The observed diel periodicitycannot be explained by variations in physico-chemical parametersor food concentration alone. The ecological significance ofthis phenomenon in the polymictic lake of Cr?teil is discussedin the light of previously published data and the hypothesesaccounting for it.     

Shifts in phenology of Bythotrephes longimanus and its modern success in Lake Maggiore as a result of changes in climate and trophy

In Lake Maggiore, the density of the invertebrate predator Bythotrepheslongimanus increased following lake re-oligotrophication inthe late 1980s. This "invasion" was followed by dramatic changesin the pelagic food web, consistent with those that followedthe establishment of B. longimanus in North American lakes whereit is not native. In this contribution, we explore the modernsuccess of B. longimanus in Lake Maggiore by investigating itsphenology and population density, and their correlations withabiotic and biotic factors during the period from 1981 to 2003.A 10-fold increase in the abundance of B. longimanus followedan earlier start and longer duration of annual population growth.Increased prey resources and decreased predation pressure werenot observed during the B. longimanus density increase. Instead,a rise in lake temperature may have altered the reproductivecycle of this species. Furthermore, the depth and duration ofa refuge from visually orienting fish predators increased duringthese 20 years, as a result of changes in the thermal stratificationregime of the lake. This case study provides a timely exampleof how climatic changes may interact with biotic drivers (e.g.fish predation) to influence the density and phenology of aninvertebrate predator.     

Implications of an invertebrate predator's ( Bythotrephes cederstroemi) atypical effects on a pelagic zooplankton community

The traditional view of predaceous zooplankton is that they prefer small-bodied prey, are hindered by morphological anti-predator defenses, and have a minor influence on zooplankton communities when fish are present. We performed a series of experiments with the large-bodied onychopod (cladoceran) Bythotrephes cederstroemi, in which we incubated this predator with known prey to determine prey preference and predation rates. We also performed an allozyme analysis of prey tissue in the gut of B. cederstroemi collected from several stations around Lake Michigan to determine what prey types are chosen in the field. We found that B. cederstroemi does not fit the standard invertebrate predator mold: adult B. cederstroemi prefer large (>2.0 mm) Daphnia pulicaria over smaller individuals; the elongated tailspine and helmet of Daphnia galeata mendotae are not effective deterrents to B. cederstroemi predation; and B. cederstroemi is a generalist predator with the potential to consume a significant portion of cladoceran production in Lake Michigan. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interactions between phytoplankton and zooplankton in a fertilized lake

The limnology of an oligotrophic lake, Langvatn, situated in Trøndelag county in Central Norway, has been studied for five years (1974–1978). In two years, 1975 and 1976, the lake was fertilized with a general fertilizer to change feeding conditions for the zooplankton. Mean phytoplankton biomass in the epilimnion and primary production for the years (1974–1978) were 417, 618, 1370, 607 and 779 mg m⁻³ and 10.6, 22.2, 49.0, 26.8 and 17.7 g C m⁻² yr⁻¹, respectively. Cladocerans were the dominant herbivore group in 1974 and 1975 and Rotifera in the next three years. The main difference in the interaction between phytoplankton and zooplankton occurred when cladoceran dominance gave way to rotifer dominance. Heavy phytoplankton grazing by cladocerans in 1974 and 1975 stabilized the biomass and maintained it at a low level, which also resulted in a relatively low primary production. The rotifer-dominated community during the years 1976–1978 did not possess the ability to maintain a stable level of algal biomass. Primary production was also relatively high during these years.     

Anti-predator behaviour of native prey (Daphnia) to an invasive predator (Bythotrephes longimanus) is influenced by predator density and water clarity

Hydrobiologia - Bythotrephes longimanus is an invasive zooplankton predator, negatively impacting zooplankton abundance and diversity in North American lakes. Previous studies have shown that...