Mountain and Arctic streams are among the harshest freshwater environments on Earth. Temperatures remain near freezing, nutrients are scarce, and ice can cover these systems for much of the year. Despite these constraints, the chrysophyte alga Hydrurus foetidus not only survives but thrives.
During its bloom season from late autumn to early spring, Hydrurus foetidus rapidly colonises these streams, covering nearly all available surfaces within days. These blooms consist of dense mats of filaments attached to stones. Each filament contains thousands of individual cells embedded within a shared extracellular matrix, forming complex and highly structured assemblages. Yet, the mechanisms that enable this alga to proliferate under such extreme conditions remain largely unknown.
This project addresses this question from two complementary perspectives.
First, we investigate nutrient utilisation and limitation in Hydrurus foetidus. We focus on which nutrient sources are accessible in these oligotrophic systems and how the alga has adapted to efficiently exploit them. Notably, Hydrurus foetidus exhibits exceptionally high enzymatic activity for phosphorus acquisition, allowing it to access organic phosphorus pools in the surrounding water. In addition, it appears capable of adjusting its pigment composition in response to variations in light and nutrient availability. We are currently working to resolve the physiological and molecular mechanisms underlying these adaptations.
Second, we explore interactions between Hydrurus foetidus and associated bacterial communities as a potential ecological strategy. Across multiple streams, we consistently observe similar bacterial taxa embedded within the algal filaments, suggesting selective recruitment by the host. These bacteria may contribute to nutrient acquisition, stress tolerance, or other functions that support algal growth. Ongoing work aims to characterise these interactions and identify their functional roles.
To address these questions, we combine field observations, controlled experiments, and laboratory analyses. We sample Hydrurus foetidus across numerous streams throughout Valais, Switzerland, while also conducting high-resolution monitoring in a focal stream, the Borgne d’Arolla. In parallel, we use artificial flume systems in Satarma (Evolène, VS) to investigate growth dynamics under controlled conditions. These approaches are complemented by laboratory experiments examining growth, nutrient content, enzymatic activity, and microbiome composition.
Project team: Stefan Eckensperger (PhD student), Aleksei Dukat (PhD student)
Visiting student: Lucie Bourgault
Fieldwork, technical and scientific support: Matteo Tolosano, Nicola Deluigi, Florian Baier, Grégoire Michoud, Hannes Peter Markus
Principal Investigator: Prof. Tom I. Battin
