Julie Conrads

I am a PhD student in Aquatic Ecology at Eawag (Swiss Federal Institute of Aquatic Science and Technology), affiliated with ETH Zurich and supervised by Dr. Alexandra Anh-Thu Weber (Weber Lab).

My PhD research focuses on the Quagga mussel (Dreissena rostriformis bugensis), an invasive bivalve that has been rapidly spreading across Swiss lakes since its first detection in Lake Constance in 2014, and was found in Lake Zurich for the first time in 2024, a discovery I made during my own benthic field surveys.

My work spans three interconnected research themes:

Benthic macroinvertebrate ecology. I conducted the first comprehensive baseline survey of the benthic invertebrate community in Lake Zurich and Obersee, sampling across seven sites at depths of 1 m, 5 m, and 15 m. Over 92,000 individuals were counted and identified, revealing that invasive species already dominate the shallow littoral zone (88% of individuals in Lake Zurich). This dataset will serve as a critical reference for tracking the ecological footprint of the ongoing Quagga mussel invasion. A paper is in preparation.

Invasion genomics. Using whole-genome sequencing of over 640 individuals sampled across Europe (Switzerland, Germany, UK, France, the Netherlands, Belgium, Denmark, Italy, Austria, Ukraine) and North America (Great Lakes, western US), I am tracing the global and regional dispersal routes of the Quagga mussel. Preliminary results reveal distinct genetic clusters and multiple independent introduction events into Switzerland, raising important questions about connectivity between water bodies and the role of shipping corridors in facilitating spread.

Reproductive biology. A further chapter investigates the reproductive success of Quagga mussels in Lake Constance, examining variation across depths and seasons, an important dimension of understanding why this species is so ecologically successful compared to the closely related Zebra mussel (Dreissena polymorpha).

Previously, I completed my Master’s thesis at Eawag on the conservation genomics of the freshwater mussel Anodonta anatina in Switzerland, for which I received the Hydrology-Limnology Prize for Best Master Thesis 2024 from the Hydrobiologie-Limnologie-Stiftung für Gewässerforschung.

I hold a BSc from the University of Zurich with a major in Geography and a minor in Biology, and an MSc from the University of Zurich / ETH Zurich. I am a member of the Eawag Scientific Dive Unit, which supports my fieldwork in Swiss lakes.