Unexpected distribution of aquatic invertebrate communities in a threatened desert wetland: Sentenac Cienega, Anza-Borrego Desert State Park, CA

Authors: Kate Boersma, Rainier Cardin, Janelle Doi, Jessica Cidrao

Year: 2022

Abstract

Sentenac Cienega is a wetland in the Colorado Desert of Southern California that has experienced rapid drying over the past two decades and now holds surface water for only a few months per year. The Cienega is in the headwaters of the San Felipe Creek watershed and forms a transition point between perennial reaches upstream and non-perennial reaches downstream. As such, the wetland may be an important dispersal corridor for flying aquatic invertebrates moving downstream to colonize temporary aquatic habitats. Here we report the results of: 1) a four-year field study comparing aquatic invertebrate communities upstream and downstream of the wetland, and 2) a mesocosm experiment measuring invertebrate colonization of novel downstream habitats. Overall, we found very little overlap in invertebrate community composition between perennial and non-perennial stream reaches, even among sites located within 1km of each other. Additionally, in the mesocosm experiment, taxa from perennial reaches rarely colonized novel artificial habitats downstream. Sentenac Cienega appears to act as a dispersal barrier instead of a dispersal corridor as predicted, which contradicts expectations based on prior research in nearby streams. It is likely that unique local conditions in the San Felipe Creek watershed, such as anthropogenic influences and complex groundwater dynamics, contribute to the unexpected distribution of aquatic invertebrates that we observed. Our data will inform an ongoing collaboration with hydrologists, cultural anthropologists, terrestrial ecologists, and land managers to develop a restoration plan to protect the future of this biologically and culturally important area.