Population dynamics of the invasive freshwater shrimp Neocaridina davidi in the thermally polluted Gillbach stream (North Rhine-Westphalia, Germany)

Abstract

Ornamental species of the aquarium pet trade contribute more and more to the introduction of previously exotic species in Europe. Among these, freshwater crustaceans play an increasingly larger role. Especially in thermally altered streams they may become invasive; however, field data on population ecology of invasive crustaceans are very rare. The aim of this study was to analyze the population dynamics of the invasive freshwater shrimp Neocaridina davidi (indigenous to China and other Asian countries) in a year-round warm-water habitat in the Gillbach stream (North Rhine-Westphalia, Germany), where this species forms a stable population. The species reached abundances between 0.23–1.39 individuals per m². N. davidi is highly productive and detectable in the whole Gillbach stream and in the lower Erft River, too. Egg ratio and cohort development were documented for a period of 27 months. Among adults, between 45 and 59% were females (average 50.5%). Life span was about 12 months in the field and up to 21 months under laboratory conditions. Development times under field and laboratory conditions were similar, ovigerous females appeared about 7 months after hatching. The population in the Gillbach stream was multivoltine with about two generations per year. Only 2–3% of eggs reached adulthood in the field most probably due to intensive predation by indigenous and invasive fish species. One specimen could already be detected in the Lower River Rhine. N. davidi is omnivorous and well adapted to different freshwater habitats. The risk of further spreading to other European river systems is obvious.