Invasion stage of the exotic snail Melanoides tuberculata related to environmental and biological factors in a subtropical river drainage

The mollusks represent the main invasive taxon of the freshwater ecosystem in North America. Environmental degradation may increase the susceptibility of the ecosystem to invasion and favor the abundance and density increment in some benthic mollusks. Melanoides tuberculata is a snail native from Africa and Asia that was introduced in Mexico in the sixties through aquarium activities. Its reproduction by parthenogenesis, fast growth, longevity, omnivore habits, and wide tolerance to pollution and environmental stressors, confers to this snail great capability like invasive species. However, the information concerning the relationships between the invasion stage of this exotic snail and environmental and biological variables is still unknown. This study aimed to document the establishment of several new registered populations of M. tuberculata in subtropical river drainage in central Mexico, since at least 10 years ago, and its relationship with indicator variables of environmental degradation. We visited 15 localities during the dry season in 2016 and 2022. At each study site, the macroinvertebrate assemblages were collected, and physical variables of habitat and physicochemical water characteristics were measured. In addition, the biological condition was assessed using aquatic macroinvertebrate assemblages. Each individual of M. tuberculata was counted and measured. The abundance and density of the snail with physical, chemical, and biological variables were correlated, and further multivariate analyses were performed to confirm these relationships. We demonstrated a positive relationship between the presence, abundance, and density of M. tuberculata with environmental variables that are indicators of degradation of physical attributes such as water flow alterations and loss of habitat heterogeneity in 2016 and 2022. We supported the hypothesis that anthropic habitat degradation can favor the invasion of M. tuberculata. The distribution of M. tuberculata was determined by the physical conditions of the ecosystem, not by the flow pattern of the river. Anthropogenic habitat degradation, such as flow regime loss and loss of habitat heterogeneity favors the establishment of M. tuberculata. The establishment and spread of M. tuberculata depended mainly on the physical attributes of the habitat, rather than on biological or chemical factors.