Isolated oases in the Sierra El Aguaje, Sonora, México: a biological inventory of aquatic animal species

Authors: Michael T. Bogan, Nohemí Noriega-Felix, Sylvette L. Vidal-Aguilar, Oscar Gutierrez-Ruacho, Andrés Alvarado-Castro, Lloyd T. Findley, Alejandro Varela-Romero, David A. Lytle

Year: 2008 (xl)

Abstract

Desert spring systems support a remarkable diversity of aquatic organisms given their arid surroundings. The spring-fed oases of the Sierra El Aguaje are small patches of aquatic habitat and tropical vegetation isolated from one another by formidable volcanic cliffs and expanses of desert. This physical setting predicts that oases of this mountain range have great potential for high diversity and endemism of aquatic organisms. We quantified habitat types and sampled the aquatic biota of eight oases in the Sierra El Aguaje during spring and summer of 2008. We documented over 150 species of aquatic invertebrates and 4 species of aquatic vertebrates (2 frogs, 1 snake, and 1 fish) from 4 habitat types (riffle, seep, tinaja, oasis) among these 8 sites. Riffle, seep, and lentic (tinaja/oasis) habitat types each supported unique species and distinct communities of invertebrates. Additionally, these invertebrate communities are mainly of Neotropical origin and distinct from aquatic communities in other regions of Sonora (e.g., the Madrean Sky Islands). Preliminary examinations by taxonomic experts indicate that we likely collected several new species of invertebrates. The small sizes and isolation of these oases, combined with the reliance of many species on regionally rare and fragile microhabitats (e.g., riffles), make these systems extremely vulnerable to anthropogenic disturbance. Climate change and the rapidly-growing tourist destination of San Carlos both pose significant threats to this unique and diverse biota and we hope that our survey results contribute to effective conservation planning in the ecologically unique Sierra El Aguaje.