San Bernardino Springsnail Pyrgulopsis bernardina
ESA status: threatened

San Bernardino springsnails empty shells pc William RadkeSouthwestern springsnails like to seek the source of things – they are most commonly found in “rheocrenes,” the technical term for a spring emerging from the ground as a flowing stream. Spring vents offer clean, clear water of consistent temperature and flow as well as stable vegetative and algal composition, which explains springsnails’ affinity for them. The San Bernardino springsnail is no exception. It prefers shallow springs with cobble substrates, fast-flowing, well-oxygenated water, and dense vegetation. These tiny springsnails have narrow, conical shells no bigger than a pencil point. They are completely aquatic, breathing through an internal gill, and live only 9 to 15 months on average.

The San Bernardino springsnail’s historic range in the U.S. was restricted to springs at the headwaters of the Rio Yaqui in southern Arizona on the San Bernardino National Wildlife Refuge (NWR) and the state-owned John Slaughter Ranch Museum. The species has been extirpated from all but two springs: Goat Tank Spring and Horse Spring on the John Slaughter Ranch Museum. Across the border, the San Bernardino springsnail occurs at five sites in Sonora, Mexico, all located on privately owned ranches. The springs at these sites are known as “ciénega” ecosystems (wet, marshy areas where groundwater bubbles to the surface), and most of the sites contain several springheads serving as habitat for this rare snail.

Impoundment and inundation of springheads has flooded some of the springs where the San Bernardino springsnail once occurred, turning them into still ponds unsuitable for this exacting invertebrate. Other springheads face the opposite problem: water loss from pumping and  diversion. All of the springs in Arizona and Mexico where the San Bernardino springsnail lives (or lived) likely have their source in the same aquifer, making them all vulnerable to groundwater depletion. For example Snail Spring on the John Slaughter Ranch Museum, once home to a high density of springsnails, has not flowed consistently since 2005 due to water withdrawal for irrigation and other use, and the San Bernardino springsnail population has disappeared from the springhead. In an attempt to mitigate the damage and restore the habitat, the San Bernardino NWR and the John Slaughter Ranch Museum drilled a well in 2011 that flows directly to Snail Spring, supplementing the waterflow. Climate change and drought are also likely threats to spring habitats in the American Southwest now and in the future. San Bernardino springsnail habitat has already suffered reduced spring flow, and continued drying could lead to more local extirpations of springsnail populations.

The FWS has designated four springs as critical habitat for the San Bernardino springsnail in the U.S.; two are occupied and two are not. Because this species has a naturally small range, it is more susceptible to catastrophic events like floods or fires, which have the potential to destroy its entire range. The unoccupied springs, Snail Spring and Tule Spring, will hopefully serve as new sites for the species to increase their population and resiliency.

photo credit: William Radke