Creating Refuges for the Axolotl (Ambystoma mexicanum)

Cropping in the naturally fertilized Xochimilco wetlands during seasonal floods helped Aztecs to build one of the most advanced civilizations of the Americas. At the edge of Mexico City, Xochimilco hosts more than 140 migratory birds and an endemic crayfish (Cambarellus montezumae) and fish (Menidia humboldtiana). It is the last remnant habitat of one of the most iconic animals from central Mexico: the axolotl (Ambystoma mexicanum) (Figure 1). This salamander has been associated with Mexican culture as twin of the most important Aztec god Quetzalcoatl and inspiration for writers and philosophers.

Mexico City requirements for ecosystem services provided by Xochimilco wetlands have intensively perturbed this aquatic system in the last 60 years. Its water quality has decreased, with high bacteria, nutrient, and heavy metal concentrations (Zambrano et al. 2009). Consequently, axolotl populations have decreased alarmingly in the last decade, with high probabilities of extinction in the wild by 2019 (Zambrano et al. 2007). The few remaining populations are scattered and isolated, and therefore restoration measures are critical.

Top-down management and restoration attempts in Xochimilco have not worked, leading to abandonment of traditional agriculture for greenhouse production, reducing even more the water quality and axolotl habitat. An aquaculture fish introduction program resulted in an overabundance of tilapia (Oreochromis niloticus) and carp (Cyprinus carpio), which affect axolotl populations by predation and modifying food webs. A program of axolotl reintroduction conducted by an academic institution and sponsored by local government, using salamanders grown in captivity, is not expected to increase population numbers (see Zambrano et al. 2007). Moreover, if siblings are used for the introduction program, the genetic diversity of wild populations may be reduced.

Long-term success of restoration measures requires involvement of local people in the management program (Gall and Staton 1992). Scientists together with local farmers (chinamperos) are working to create an alternative axolotl restoration program. Traditionally, these local farmers produce in “chinampas,” which are land structures forming a labyrinth of canals connecting lakes and wetlands (Contreras et al. 2009). Chinamperos use canal sediments for cropping, reducing chemical fertilizers. Also, canals surrounding the chinampas increase the wetlands’ spatial heterogeneity that seems to be necessary for axolotl survival. This indicates that it is necessary to conserve the traditional agriculture in order to restore the wetland.

By sharing information with chinamperos, we have enough ecological and empirical knowledge about the axolotl to create a restoration program focused on improving its habitat. We now understand that population dynamics depend mostly on the survival of eggs and larvae (Zambrano et al. 2007), which is closely related to plants used by females to lay their eggs (Valiente 2006, Marín 2007). The axolotl is at the top of the food web, but shares most of its food sources with the non-native carp and tilapia (Zambrano et al. 2010). Axolotl distribution is limited to a few small canals, surviving away from urban and greenhouses areas (Contreras et al. 2009). City demand for Xochimilco ecosystem services makes it impossible to restore the entire wetland, and isolating the conservation of the axolotl from human activities will break the already weak link between the salamander and citizens. Therefore chinamperos and scientists decided to generate refuges within chinampas border canals.

Figure 1.

The Xochimilco wetlands (top) next to Mexico City provide habitat for the culturally iconic axolotl (Ambystoma mexicanum), an aquatic salamander (bottom) that is rapidly disappearing from the increasingly degraded wetlands and has been bred in captivity in early restoration efforts. Photos by Luis Zambrano (top) and Carmen Loyola (bottom)

Canals used as refuges were isolated from the system with rustic filters to exclude non-native fish and improve the water quality (Figure 2). Many chinamperos water their lands manually by carrying water from the canals, and improved water quality will also yield farm products that test free from bacteria and heavy metals, which allows chinamperos to better market their products. This partnership helps both the axolotls and the chinamperos by improving habitat and preserving traditional agriculture.

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