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 systems 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 National Park and Mont Avic Natural Park 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.

“The loss of cold-adapted zooplankton is not just the disappearance of unique species—it represents a functional shift in the ecosystem. These dynamics are an early warning of what may happen in similar high-altitude regions around the world,” the researchers conclude.

They’re everywhere, but they’re small. Sometimes not so small as to be invisible: with a bit of patience and good lighting, some can be spotted with the naked eye as tiny moving specks in the water. But to truly appreciate their unusual shapes and diversity, you need a closer look. Under the microscope, a world full of bizarre structures and creatures is revealed —many of them seemingly from another planet.

In this post, we invite you to discover some of these fascinating little inhabitants of alpine lakes.

• Alona

This small cladoceran lives in the littoral zone of the lake, near the shore. The specimen shown here is a female carrying a large egg in a dorsal pouch. She keeps it protected there until the offspring is fully developed —an effective strategy in cold, unpredictable environments.

• Cyclops abyssorum

Measuring about 2 mm in length, this predatory crustacean is easily recognized by its single large eye on top of its head —hence the name. It lives near the bottom of the lake. Although its long antennae look menacing, they aren’t used for hunting: the male uses them as clasping tools during courtship.

• Keratella cochlearis

At first glance, it looks more like a flower than an animal. This tiny rotifer, just 0.1 mm long, swims in search of microalgae and bacteria, propelled by a ciliated organ near its upper spines.

• Daphnia longispina

This species can grow up to 2.5 mm, and its large compound eyes give it an almost endearing expression when seen under the microscope. It is one of the most common cladocerans and a key species in lake food webs, thanks to its voracious appetite for algae.

• Chydorus sphaericus

Round and charming, this is the smallest crustacean in the group, measuring between 0.2 and 0.5 mm. It is a cosmopolitan species and considered the most widespread cladoceran in the world, found in a wide variety of freshwater habitats.