The axolotl and the remnants of Mexico City’s ancient wetland

Ambystoma mexicanum (axolotl) is critically endangered. Photo credit: Giulia van Pelt, giuvanpelt on Flickr
Guillermina Echeverria-Lozano
17 May 2018

MEXICO CITY (Landscape News) — Mexico City’s ancient system of water channels and lakes provide a home for one of the world´s most charismatic amphibians: Ambystoma mexicanum, the Mexican salamander.

Known locally as an axolotl in Nahuatl language, it is an endemic species to the complex lagoon system, which 300 years ago encompassed the lakes of Texcoco, Xochimilco, Chalco, Zumpango and Xaltocan. Mexican axolotls are now found only in nature in the Xochimilco wetlands.

Often referred to as a “walking fish,” unlike other salamanders the axolotl keeps its larval attributes throughout its entire lifespan, a condition known as neoteny. It keeps dorsal fin, which looks like a tadpole and is almost the full length of its body. It also retains external gills which stick out on the back of its head.

The Xochimilco area, characterized by canals that cut through farmland frequented by flat-bottomed boats carrying tourists, represents only 2 percent of the original massive wetland system, considered a UNESCO World Heritage site, that once covered the Valley of Mexico.

Conservation efforts to protect the axolotl and its shrinking habitat face challenges on many fronts from urban development, agricultural practices, poor water quality and unregulated tourist activities.

The axolotl has been listed as critically endangered on the International Union for conservation of Nature (IUCN) Red List since 2006. The main threats it faces are consumption, invasive species (carp and tilapia) and an inefficient sewer system that overflows and releases human waste into the Xochimilco system whenever it rains heavily.

Like many other amphibians around the world, the axolotl is facing extinction in the wild. If current trends continue it could disappear within the next 10 years, according to Luis Zambrano, a researcher at the National Autonomous University of Mexico.

Ambystoma mexicanum had a prominent role among pre-Columbian cultures and at that time it was very abundant in the Valley of Mexico. The axolotl population dropped from 6,000 individuals per square kilometer 20 years ago to less than 100 per square kilometer 10 years ago, Zambrano says. Today, the surviving wild population in Xochimilco is estimated to be less than 35 individuals per square kilometer.

As one of the most widely studied amphibians — as a model organism in regenerative medicine, development science and cancer research — several Mexican axolotl captive colonies exist around the world. However, captive bred colonies are fragile and may lack the genetic diversity ensuring their long-term survival both in captivity and in the wild.

Additionally, reintroduction is not recommended unless current threats can be mitigated. In other words, Xochimilco might be the axolotl´s last chance to survive.

Xochimilco and the other lakes, were once an important part of the livelihoods of one of the most important civilizations in the Americas.

The hydrological and physical characteristics of these lakes were first modified about 1,000 years ago with the construction of pre-Columbian agricultural plots known as chinampas, which were created to allow crops to flourish, benefitting from the freshwater lakes. The unique and ancient agricultural system of artificial islands (or “floating gardens”) is created with reeds and sticks into which surrounding vegetation and fertile soil are built up to form a bed on which to grow crops.

The chinampas are fertilized with soil from the bottom of the lake, allowing nutrients to be renewed year after year.

Chinampas are an example of a sustainable use of the wetland ecosystem and they are still common in Xochimilco. The islets vary in size, but on average measuring roughly 20 x 200 m. Additionally, chinampas create spatial heterogeneity and increase the resilience of the ecosystem.

The habitat of the axolotls is found within the 180 km of channels between the chinampas.

Zambrano´s group along with local producers and other academic groups, have created refuges at Xochimilco on isolated channels between chinampas by building natural filters made of stones, gravel and aquatic plants.

These filters improve water quality and prevent exotic fishes from entering. There, wild Mexican axolotls can reproduce and grow in safety.

Local users of the chinampas are encouraged to use them in a way that most suits them. For Zambrano, a leading expert in axolotl conservation, heterogeneity is an asset for the axolotl conservation project, as well as for other local flora and fauna. He believes that this diversity increases biodiversity.

The Xochimilco wetlands are also home to many other native species of flora and fauna (including more than 100 species of migratory birds) and help to filter water, amongst other ecosystem services. It has been suggested that Xochimilco provides Mexico City with more than $15 million in ecosystem services per year, including carbon capture and an improvement in water quality.

Due to its charisma and attractiveness, the axolotl has recently been used as a flagship species to protect the Xochimilco wetlands. As a result of this recent interest, several social, academic and governmental groups are now working on the axolotl´s conservation.

In recent years, the axolotl has effectively increased public awareness of the environmental significance of the area. Thus, the survival of the axolotl might also be Xochimilco´s last chance to survive.

Interest in the intriguing creature has increased to such an extent that now the attractiveness of the axolotl threatens to overwhelm the significance of the Xochimilco wetlands in some cases, demonstrating how the fate of the two are entwined.

Interest in the axolotl is becoming greater than the ecosystem that sustains it, according to Luis Zambrano and his colleagues who say it is vital to maintain the connection between the survival of the species (the axolotl in this case) and the conservation of its ecosystem.

As a new stage of his project is beginning this month, Zambrano feels optimistic about the future of the axolotl: “If we had at least 150 chinampas with refuges (with one or two axolotls per square meter), we could boost axolotl wild population survival,” he says.

Join International Union for Conservation of Nature (IUCN) at the Global Landscapes Forum Third Investment Case in Washington for a panel discussion on The Many Faces of Blended Finance for Forest Landscape Restoration on May 30. 


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