VICKSBURG, Miss. — Researchers with the U.S. Army Engineer Research and Development Center (ERDC) are working with the Mississippi Museum of Natural Science to examine the habitat association, distribution levels and substrate preference of the Big Black Rocksnail.
After the 1989 chemical spill in Mississippi’s Big Black River, the U.S. Fish and Wildlife presumed the entire Big Black Rocksnail population perished because the species could not be located. For decades, fish or mussel surveys were not conducted in the Big Black River by the U.S. Army Corps of Engineers or state agencies. Then in 2021, the Mississippi Museum of Natural Science performed a longitudinal survey of the diverse mussel community in the river, and a shell of the freshwater snail species was found. A year later, scientists went back to the marked site and discovered thousands of the snails upon the gravel bar.
Dr. David Ruppel, a research fisheries biologist with ERDC’s Environmental Laboratory joined the team in 2023 to assist with identifying habitat associations and the full range of the freshwater species.
“It’s insane seeing how dense they are. I think we have calculated that in the main bed, or the Mothership as we like to call it, there are about 600 snails per square meter,” said Ruppel.
The particular freshwater species of snails has only been found in a five-kilometer stretch of the Big Black River, therefore having one of the smallest ranges of any endemic snail species in North America.
This is very unusual considering species with small distributions are normally spring associated.
“You’d expect a wider distributional range because they are not spring associated, so at this time we really don’t know what is driving their distribution,” said Ruppel. “For spring associated snails, mussels or fish, they typically tend to be in the system because of stable factors such as water quality, temperatures, PH level and conductivity; however, there is no spring influence on the Big Black Rocksnail, so we are performing studies to understand why there is a limited distribution.”
This year, laboratory-based studies will be performed to test water quality; substrate suitability such as gravel, cobble, bedrock and sand; depth in the water column and what current velocity they can withstand.
The researchers are hopeful to conduct field studies next year in order to calculate substrate depth, maximum current velocity and the number of snails in an area.
“We will take a string from one bank to the other and drop a quadrat at one-meter intervals to sample the distribution area,” said Ruppel. “We will perform this research method at multiple points in the river to learn if there is a specific area they tend to be more associated with, the type of substrate they tend to favor and the current velocity they can tolerate.”
The results will guide the researchers in determining the snails’ primary drivers. Furthermore, the knowledge will assist researchers in finding a suitable habitat for the snails if at some point they need to be reintroduced into the wild or translocated to another area of the river to extend their range.
With time, these factors will aid in creating more redundancy within the population and help the recovery of an imperiled species in the state of Mississippi.