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Dreissenid mussels (including the zebra mussel Dreissena polymorpha and the quagga mussel D. rostriformis) are among the world's most notorious invasive species, with large and widespread ecological and economic effects. However, their long‐term population dynamics are poorly known, even though these dynamics are critical to determining impacts and effective management. We gathered and analyzed 67 long‐term (>10 yr) data sets on dreissenid populations from lakes and rivers across Europe and North America. We addressed five questions: (1) How do Dreissena populations change through time? (2) Specifically, do Dreissena populations decline substantially after an initial outbreak phase? (3) Do different measures of population performance (biomass or density of settled animals, veliger density, recruitment of young) follow the same patterns through time? (4) How do the numbers or biomass of zebra mussels or of both species combined change after the quagga mussel arrives? (5) How does body size change over time? We also considered whether current data on long‐term dynamics of Dreissena populations are adequate for science and management. Individual Dreissena populations showed a wide range of temporal dynamics, but we could detect only two general patterns that applied across many populations: (1) Populations of both species increased rapidly in the first 1–2 yr after appearance, and (2) quagga mussels appeared later than zebra mussels and usually quickly caused large declines in zebra mussel populations. We found little evidence that combined Dreissena populations declined over the long term. Different measures of population performance were not congruent; the temporal dynamics of one life stage or population attribute cannot generally be accurately inferred from the dynamics of another. We found no consistent patterns in the long‐term dynamics of body size. The long‐term dynamics of Dreissena populations probably are driven by the ecological characteristics (e.g., predation, nutrient inputs, water temperature) and their temporal changes at individual sites rather than following a generalized time course that applies across many sites. Existing long‐term data sets on dreissenid populations, although clearly valuable, are inadequate to meet research and management needs. Data sets could be improved by standardizing sampling designs and methods, routinely collecting more variables, and increasing support.

Bighead carp (Hypophthalmichthys nobilis), silver carp (H. molitrix) and their hybrids (collectively referred as Asian carps−AC) are primarily planktivorous cyprinid fishes that have been introduced into more than 30 countries around the world, including Hungary. However, recent studies demonstrated that AC can adversely affect the water quality and native fish populations. In this study, we report on the rate of hybridization, growth parameters and feeding habits of AC, to assess their ecological impacts and life history traits in the oligo-mesotrophic Lake Balaton. We found that the majority of the investigated AC (n=116) were hybrids. In general, hybrid AC with silver carp characteristics dominated the stock (90%), but 10% of individuals exhibited bighead carp phenotype and the proportion of bighead carp genes exceeded 98% in 4 individuals. However, the variance in phenotypes and the rate of hybridization did not influence significantly the feeding habits. Rather, the food composition was determined by the availability of different food resources and the concentration of suspended inorganic particles in the ambient water. Stable isotope analyses and microscopic analyses of gut contents revealed that the vast majority (>99%) of the ingested and metabolised food was zooplankton (mainly Rotifers, Cladocerans and Copepods). Despite the low proportions of algae in the food, we identified 155 phytoplankton taxa in the foregut-contents, among which there were several species (e.g., Scenedesmus spp. and Microcystis spp.) that survived the passage through the guts. Growth rates of AC were intermediate in Lake Balaton, while their condition factors were relatively high compared with other ecosystems. The relatively high condition factors were particularly interesting in the light of the high inorganic matter content of ingested food (43±9% in dry mass). We conclude that the presence of AC is an ecological threat to Lake Balaton, because AC can be important resource competitors of native planktivores.