A new scientific study – published in the journal Biological Conservation and led by the LIFE RESQUE ALPY project, coordinated by CEAB-CSIC- has documented a fast disappearance of cold-adapted zooplankton in high-altitude lakes of the Western Alps. These microscopic organisms, which serve as key bioindicators of ecological health, are declining as a result of global warming and the introduction of non-native fish species—even in protected areas.
Alpine lakes are undergoing deep and rapid ecological changes. The findings, based on 643 samples collected between 2006 and 2024 from 101 lakes and ponds, reveal a significant regression of cold-specialist species such as Arctodiaptomus alpinus and Daphnia pulicaria. These species, highly sensitive to environmental disturbances, offer crucial signals of the ecological balance in high-mountain aquatic ecosystems.
“Alpine lakes act as ecological sentinels. Despite being located within protected areas, they are undergoing a silent but profound transformation. The decline of cold-adapted species is a clear warning of the combined impact of global warming and local human pressures,” explains Rocco Tiberti, lead researcher and first author of the study.
A fragile and threatened ecosystem
Zooplankton play a fundamental role in aquatic food webs. In mountain lakes—often naturally fishless—these communities typically occupy the top of the pelagic food chain. The introduction of exotic species, mainly trout and cyprinids, disrupts this balance and promotes the loss of larger, more vulnerable zooplankton taxa.
Added to this pressure is climate change, which has led to a rise of over 1°C in the average annual temperature in the region in less than two decades. This warming trend affects ice cover dynamics, accelerates thawing, and reduces the availability of suitable habitats for cold-adapted species. The result is a marked “thermophilization” of aquatic communities: cold-loving species are being gradually replaced by others better adapted to warmer conditions.
“This is a phenomenon we observe in other ecosystems under climate stress, but here the impact is more direct and more visible due to the simplicity of these food webs,” adds Tiberti.
In addition to their ecological function, zooplankton also serve as sensitive bioindicators of lake health. Shifts in their composition and abundance reflect a range of environmental changes, from temperature increases to species introductions and diffuse pollution.
Towards active management of mountain lakes in the face of global change
Despite the worrying outlook, the study highlights that action is still possible. Effectively protecting pristine lakes—especially medium to large ones that remain fish-free—and restoring degraded ones by eradicating invasive species are both feasible and already underway in several protected areas.
As part of the LIFE RESQUE ALPY project, national parks such as Gran Paradiso, Mont Avic or Pyrenne’s natural parks are implementing restoration actions in high-mountain lakes, with promising early results.
Furthermore, the retreat of Alpine glaciers is giving rise to new proglacial lakes, which could become important refuge habitats for sensitive species. Careful management of these newly forming ecosystems could help safeguard a portion of the region’s threatened aquatic biodiversity.
The study’s authors emphasize that high-mountain lakes are ecosystems of exceptional ecological and scientific value. Their structural simplicity makes them ideal natural laboratories for studying the effects of global change, but it also renders them particularly vulnerable, with limited capacity to buffer rapid disturbances.
