Biodiversity of American rivers analyzed over 30 years

In 2021, Professor Frédérik De Laender was approached by American researchers to contribute to a study on the evolution of aquatic diversity in rivers in the USA. The aim: to analyze changes in aquatic diversity and identify the factors behind them. To answer this question, the researchers analyzed data collected over thirty years, covering 389 fish species in nearly 3,000 rivers and streams.

"There was already a lot of data on aquatic diversity in the USA, but it was scattered, recorded in different formats and produced using a variety of techniques and methodologies," explains Frédérik De Laender. "The challenge was therefore to harmonize them, in order to form a coherent whole, capable of revealing trends over several decades and on a continental scale."

In this study entitled "Diverging fish biodiversity trends in cold and warm rivers and streams" researchers studied 389 fish species in 2,992 rivers and streams, between 1993 and 2019. The results show contrasting trends depending on water temperature:

• In cold waters (< 15.4°C), the number of fish fell by 53% and the number of species by 32%. Small fish have declined, replaced by larger species often introduced for sport fishing.
• In warm waters (> 23.8°C), by contrast, the number of individuals has increased by 70% and diversity by 16%, with small opportunistic species dominating.
• Intermediate streams (15-24°C) showed little change.

These trends show that temperature changes and the introduction of certain fish species for fishing are helping to transform local aquatic communities.

Frédérik De Laender is a theoretical community ecologist who studies the links between environmental change, biodiversity and ecosystem functioning. Primarily focused on modeling, he has also conducted experiments on plankton and contributed to meta-analyses. His work focuses in particular on ecological stability and coexistence, to better understand the mechanisms that determine community composition.