Although freshwater only makes up about one percent of our planet’s surface, it is home to around ten percent of all known species. However, it was largely unclear how endangered the freshwater fauna is. Researchers have now assessed the endangerment status of the more than 23,000 known species of freshwater animals in detail for the Red List of Threatened Species. Accordingly, 24 percent of the species examined are threatened, including by water pollution, dams, agriculture and invasive species. The results can help better tailor conservation efforts to freshwater animals.
For decades, the International Union for Conservation of Nature (IUCN) has published Red Lists of Threatened Species, on which it indicates the extent to which numerous groups of organisms and species are endangered. While the Red Lists contain detailed information on birds, mammals, amphibians and reptiles, animals that predominantly live in freshwater have so far remained largely ignored. Previous protection efforts have therefore been based more on the known information about land animals. In contrast, abiotic factors such as water quality were primarily used to protect freshwater ecosystems.
Red list of threatened freshwater animals
“However, these data are insufficient to reflect the specific needs of freshwater species and achieve biodiversity goals,” explains a team led by Catherine Sayer from the IUCN in Cambridge, UK. Sayer and her colleagues therefore analyzed the endangered status of 23,496 species of freshwater animals for the Red List of Threatened Species – including fish, insects with aquatic larvae such as dragonflies and crustaceans such as crabs, crabs and shrimps.
“Our analysis shows that 24 percent of the species examined are endangered, critically endangered, threatened with extinction or already extinct in the wild,” report the researchers. “This value is comparable to that of land animals, of which 23 percent are threatened.” Sayer and her team recorded the highest percentage of threatened species at 30 percent for crustaceans, followed by 26 percent for freshwater fish and 16 percent for dragonflies. However, the researchers point out that these values are subject to great uncertainty, as reliable data is missing for 23 percent of the species examined.
Threats from pollution, dams and agriculture
The research team identified water pollution as the most important threat, endangering 54 percent of threatened freshwater species. 39 percent are affected by dams and water withdrawals, 37 percent by land use changes and agricultural impacts. Invasive species and diseases contribute to the endangerment of 28 percent of threatened species.
These factors have a specific impact on freshwater species, making them inadequately covered by general conservation efforts focused on terrestrial animals, Sayer and her colleagues explain. For example, the areas in which particularly threatened terrestrial animals occur hardly overlap with the habitats of particularly threatened freshwater animals. According to the researchers, abiotic factors such as water quality are also unsuitable as a benchmark for protection efforts.
“Conservation efforts that rely on abiotic factors can lead to suboptimal or even harmful results and should therefore be reevaluated,” write Sayer and her team. “We hope that our global IUCN Red List dataset for freshwater species can help introduce evidence-based strategies to halt further loss of freshwater biodiversity.”
Source: Catherine Sayer (IUCN (International Union for Conservation of Nature), Cambridge, UK) et al., Nature, doi: 10.1038/s41586-024-08375-z