Genetic and ecological characterization of the invasive freshwater jellyfish Craspedacusta sowerbii

点击翻译按钮获取中文摘要

A consequence of the increasing mobility and connectivity of human populations is the rising introduction of non-native species into ecosystems. In case of the non-native freshwater jellyfish Craspedacusta sowerbii the introduction of this species created a new functional guild within freshwater plankton communities, as jellyfish were not represented in European lake communities for millions of years. The freshwater jellyfish Craspedacusta sowerbii (Lankester 1880) is originating from Asia (China) and known to be present in German lakes since about 100 years. Today records from at least 100 different locations are known and according to available knowledge jellyfish within populations are unisexual and assumed to be genetically identical suggesting the spread of only one or few successful clones. Craspedacusta sowerbii has a metagenetic and meroplanktonic life cycle, including a small (1-2 mm) benthic polyp reproducing asexually. C. sowerbii may be already far more distributed as suggested by observation of medusae (1-2 cm in size). The small polyp may often be unnoticed and records of mass occurrences of the free-swimming medusoid stage predominate. Above a certain water temperature polyps can release medusae into the pelagial. Predicted increasing water temperatures can therefore result in a fast increase of the distribution of medusae. Hence, with observed individual numbers up to 1000 ind/m-2 effects of medusae on aquatic food web dynamics are expectable but not specified in detail yet. In laboratory experiments food selectivity, assimilation and ingestion efficiencies of the carnivore jellyfish will be determined, giving basic information on competitiveness with other planktivorous organism. Field mesocosm experiments along jellyfish abundance gradients will investigate trophic positions of jellyfish, cascading effects down to phytoplankton and pelagic-benthic fluxes of energy and matter mediated by jellyfish. Additionally, field surveys will investigate and compare pelagic food web dynamics in lakes containing jellyfish or not. The field surveys will allow to analyse the association between sex, genotype and environment and will help to answer questions regarding long-time establishment and evolutionary dynamics of jellyfish. Genetic diversity and population structure of C. sowerbii will be studied using high-resolving microsatellites and ITS and COI markers. Genetic analyses will show if different genotypes are present in the polyp and consequently in the medusoid stage, if only one clone is dominant or if multiple introductions are likely. The combined analyses of the genetic diversity and the ecological function of this species will allow a better understanding of cause and effect relationships within aquatic food webs exposed to invasion by non-native species.