An interview with Univ.-Prof. Dipl.-Ing. Dr. nat. techn. Kristina Sefc from the University of Graz.

“Searching for the cryptic species of freshwater shrimp feels like a sport.”

The water rushed over my boots as I carefully held the net against the current, stirring up the sediment. When I lifted the net and saw the swarming mass, I couldn’t help but smile. Gently, I transferred the freshwater shrimp into a glass filled with water. It was a perfect find. Each of these tiny creatures holds a story that stretches back millions of years, hidden in its DNA. This fascinating research journey began for me three years ago – a journey through the evolution of freshwater shrimp.

The Hidden World of Freshwater Shrimp

Freshwater shrimp are tiny yet captivating crustaceans that roam the rivers, streams, and lakes of Austria, harboring evolutionary secrets. Their current diversity traces back 20 million years, to the time of the formation of the Alps. For a long time, they were considered uniform, but modern genetic analyses paint a different picture: over 100 cryptic species, meaning species that cannot be distinguished by morphology, have been discovered. Together with bachelor’s and master’s students, the search began: samples were taken, analyzed, and mapped in the waters of Styria and Carinthia. The result is now a vividly dense map of amphipod diversity, made possible with funding from the Biodiversity Fund of the Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation and Technology (BMK). The waters along the eastern Alpine foothills are home to lineages that, based on their age, can be traced back to surviving the Ice Age. This research now provides insights into the adaptability of these creatures and offers important knowledge about the biodiversity of our local rivers. A particular fascination for Dr. Sefc lies in the genetic diversity of Synerella shrimp, which she primarily discovered in eastern Austria. Initially, they were suspected to be an invasive species, but their genetics indicated that they are native to the region. By now, Dr. Sefc, her colleagues, and students have sequenced approximately 6,500 individual freshwater shrimp from Austria.

Each circle marks a sampling location. The colors represent the different, cryptic freshwater shrimp species. Graphics provided by Kristina Sec.

Behavior and Evolution – A Dynamic Cycle

Freshwater shrimp are not only key figures in evolutionary biology but also in behavioral biology. They consciously select their mating partners – size matters, and females resist overly persistent males. Before fertilization, the animals “snuggle” for several days. Their behavior has evolved over their long existence. Additionally, females care for their offspring by carrying them in a brood pouch for weeks. Such behaviors require specific adaptations in appearance and physiology, while environmental changes may also prompt behavioral adaptations. These interactions between environment, behavior, morphology, and function are a crucial factor in the emergence of biodiversity.

Tiny Ecosystem Engineers

In our waters, freshwater shrimp play a pivotal role in the nutrient cycle. They decompose leaf litter with remarkable speed, doing so much faster than other animals performing the same task. The decomposed leaves then become available to other organisms. At the same time, the shrimp themselves serve as a food source for juvenile fish, such as brown trout, fire salamanders, and waterfowl. “So, fallen leaves essentially turn into trout fillets,” Dr. Sefc humorously sums up.

Bioindicators for Environmental Changes

Freshwater shrimp are valuable indicators of ecological changes. Some species are extremely resilient and can survive in impaired waters. While this does not make them indicators of good water quality, they do respond sensitively to pollutants – one reason they are used in ecotoxicology as “living test strips.” The genetic diversity within different lineages affects their response to environmental toxins. Therefore, Dr. Sefc emphasizes, it is crucial to always use the same shrimp lineage for toxicological tests to ensure comparable results.

Climate Change and Invasive Species

With climate change, the delicate balance of freshwater shrimp populations faces challenges. Austria is home to several native species – such as freshwater shrimp, river shrimp, and lake shrimp – but warmer temperatures could shift their distribution patterns. While freshwater shrimp thrive in cooler waters, heat-loving species like the river shrimp benefit from rising temperatures. This means river shrimp, with their faster population growth, could become more competitive and spread more widely. Additionally, invasive shrimp species from the Black Sea region are entering via the Danube. Some of these species are highly competitive compared to the native crustaceans. One particularly intriguing question is how these new cycles will develop. Initial observations suggest that some rare lineages may be migrating upstream – a sign that the distribution patterns are already changing. Close monitoring is necessary to understand the ecological consequences of the disappearance of certain lineages.

Protecting Local Biodiversity

Mapping the diversity of freshwater shrimp is not only scientifically exciting but also essential for species conservation. Yet, it is not just large rivers that matter; even small, often overlooked water bodies – ranging from groundwater pools to roadside ditches – play a crucial role. These areas may harbor rare lineages, showing that even in hidden corners of nature, incredible biodiversity exists. Communities need to be made aware of the importance of these waters. Many people are unaware of how much rivers can be negatively impacted by artificial construction and how many streams and rivers suffer under human intervention. A better understanding of this local fauna will help implement targeted conservation measures.

A Gift from Nature

After just a few months of research, it became clear to me: the greatest diversity of these fascinating creatures is not found in distant exotic lands but right on our doorstep, around Graz. It almost feels surreal that, right here, there is a hotspot of freshwater shrimp diversity,especially after spending years traveling to Africa for my research on fish. Nature holds countless surprises, and it is up to us to discover and protect them. Sometimes, the smallest inhabitants of our waters tell the greatest stories – and that is a gift we should cherish.

An article by Carolina Leiter written in the view of Univ.-Prof. Dipl.-Ing. Dr. nat. techn. Kristina Sefc from the University of Graz. Portrait photo by Carolina Leiter, other photos by Kristina Sefc.