Long-term monitoring of water temperature and macroinvertebrates highlights climate change threat to alpine ponds in protected areas

• Published in: Biological conservation 2024-02, Vol.290, p.110461, Article 110461
• Main Authors: Fahy, Julie C., Demierre, Eliane, Oertli, Beat
• Format: Article
• Language: English
• Subjects: Boreo-alpine species; Cold stenotherms; Cold-specialist species; High-elevation ponds; Pondscapes
• ISSN: 0006-3207; 1873-2917
• DOI: 10.1016/j.biocon.2024.110461

Climate change increasingly threatens alpine natural areas and notably aquatic systems. Alpine waterbodies, such as ponds, are particularly vulnerable to changes in temperature. Their biodiversity faces rising threats, especially for cold stenothermal species. Located at high elevation (>2600 m a.s.l.), the aquatic network of the Macun catchment (35 ponds and several streams) was put under a strict protection framework in 2000 (“Swiss National Park”) to mitigate threats to alpine biodiversity. The pond network has been regularly monitored as a sentinel of change, through aquatic macroinvertebrate sampling and physico-chemical measurements. Monitoring shows an alarmingly sharp increase in summer water temperature, rising by 4 °C between 2005 and 2020 (2.7 °C per decade). In contrast, nutrient concentrations have remained low and stable over these 15 years. The aquatic macroinvertebrate species richness has also been mostly stable between 2002 and 2021, with no negative impacts on the monitored cold stenotherms. Indeed, as the ponds are located at high elevation, these cold stenotherms are still living within their thermal range. Some cold stenothermal species have colonised the ponds from lower elevations, so the Macun pondscape acts as a refuge for these migrating taxa. In synthesis, our investigation highlights the alarming abiotic condition of the high-elevation freshwater biodiversity habitats, including a sharp temperature increase. It also provides evidence that their high elevation allows theses waterbodies to remain refuges for cold stenotherms, for now. In the longer term, however, a tipping point is likely to be reached, with a potential collapse of cold stenothermal biodiversity. This demonstrates the critical need to continue longer-term monitoring of high-elevation ecosystems to assess the magnitude of the impairment and to implement suitable conservation strategies, such as enhanced protection or the creation of new suitable habitats. [Display omitted] •Water temperature increased sharply in high-elevation ponds in the last 15 years.•Warming has not yet impaired macroinvertebrate communities in high-elevation ponds.•High-elevation pondscapes (>2600 m) act today as refuges for cold-specialist species.•Protection and monitoring are required to conserve these unique alpine habitats.