An international team of researchers has published the most comprehensive study on the changing ecological communities of tropical glaciers, revealing that a number of species uniquely adapted to glacial habitats will be threatened by opportunistic species moving upward as glaciers melt.

Where prior studies have mostly examined shifts in one or a few species, this new paper, published May 6 in Ecography, examines the succession, or evolution, of the biological community on the Carihuairazo glacier in Ecuador using samples of algae, plants, aquatic invertebrates and beetles. They show that species diversity around the receding foot of the glacier has been increasing since the 1950s — but that isn't necessarily a good thing. 

"We expect that we will have an increase in diversity close to the glacier; however, if we look at a regional scale, probably we will have lost specialized species," said lead author Sophie Cauvy-Fraunié, an ecohydrologist at Institut national de recherche pour l'agriculture, l'alimentation et l'environnement in France. "The takeaway message is absolutely not that the glacier retreat will induce diversity."

Growing diversity is merely a product of the rapid melt of tropical glaciers, which is creating new opportunities for species that disperse easily. These can either be plants with small seeds blown by the wind with fungal spores, or microfauna such as collembolans, also known as springtails, which is an order of small jumping insects found in a wide variety of habitats around the world. Winds can help disperse these insects, and the blowing seeds can spread lichens, mosses and algaes. For aquatic invertebrates, aquatic larvae move through streams to migrate upward to new environments. 

Cauvy-Fraunié and her colleagues assessed these trends by taking samples of plants, algae, invertebrates and land beetles along six different zones of land and water where the foot of the Carihuairazo glacier had historically been. For example, these sections represented where the glacier shrank between 1956 and 1991, 1991 and 2001, 2001 to 2005 and 2015 to 2017, reflecting the glacier's accelerating decline. 

After analyzing the contents of their samples, the researchers found that diversity had increased across all taxa, except for algae, since the glacier melted away from the corresponding measurement zone. 

Shrinking glaciers allow pioneer species more opportunities to move into spaces typically reserved for specialists. And glaciers are shrinking at a marked pace, especially in the tropics, where glaciers are typically found in the Andes, Africa and Southeast Asia. A recent study in Nature drew on NASA satellite images to show that from 2000 to 2019, Earth's glaciers shed 267 gigatons of water — enough to cover the entire state of Pennsylvania at a height of more than 7 feet. 

As with other glaciers, tropical ones are especially threatened by climate change. Carihuairazo, for example, has lost 95% of its surface area since 1956, and will likely vanish in the early 2020s, according to the study.

While Cauvy-Fraunié's study did not specifically examine which species are threatened by the tide of opportunistic dispersers, those specialized to withstand the cold conditions of glacial ice are virtually powerless in the face of any competition. One of these species is the ice worm. These worms are the one of the few animals to live their entire lives at or below 32 degrees Fahrenheit. These worms are so sensitive to heat that 40 degrees Fahrenheit will dissolve them. 

Cauvy-Fraunié is now organizing long-term surveys of streams sourced from Carihuairazo and the quickly melting Sarenne in the French Alps, both of which are within five years of completely vanishing. She has picked these glaciers to investigate how the nearing disappearance of the glacier will affect stream conditions and species diversity. In addition to the stream surveys, Cauvy-Fraunie said she would like to study glacial ecosystems from their surface. 

The study, "Multi-taxa colonisation along the foreland of a vanishing equatorial glacier," published May 6 in Ecography, was authored by Pedro Rosero and Sophie Cauvy-Fraunié, Institut national de recherche pour l'agriculture, l'alimentation et l'environnement; Verónica Crespo-Pérez, Patricio Andino, Álvaro Barragán, Ricardo Jaramillo and Priscilla Muriel, Pontificia Universidad Católica del Ecuador; Rodrigo Espinosa, Pontificia Universidad Católica del Ecuador and Universidad Regional Amazónica Ikiam; Pierre Moret, Université de Toulouse; Mauro Gobbi, MUSE-Science Museum; Gentile Francesco Ficetola, Università degli Studi di Milano, Université Grenoble Alpes and Université Savoie Mont Blanc; Ludovic Gielly and Jérôme Poulenard, Université Grenoble Alpes and Université Savoie Mont Blanc; Fabien Anthelme, Université Montpellier; Dean Jacobsen, University of Copenhagen; Olivier Dangles, Université Montpellier and Université Paul Valéry Montpellier 3; Thomas Condom and Antoine Rabatel, Université Grenoble Alpes; Rubén Basantes, Universidad Regional Amazónica Ikiam; and Bolívar Cáceres Correa, Instituto Nacional de Meteorología e Hidrología.