Shrubs and slugs

Sep 082008
Authors: Jim Sojourner

Biology Professor LeRoy Poff’s bushy, unkempt mustache bristled as he rocked in his faded chair, his eyes gazing upward at the ceiling. But Poff was not thinking about the condition of his small, lab-like office or the charts beaming from his computer screen. Poff was pretending to be a fish.

“Most people can relate to fish,” Poff said.

He often uses this empathy to explain the vicious effects of the New Zealand mud snail on the common fish, whose food is often completely consumed by invasive species like the snail.

Those invasive species, which are unnaturally introduced to certain areas and can upset the ecosystem, are truly the object of the professor’s thoughts, he said.

The saltcedar — a deciduous shrub that often interrupts natural aquatic systems — and the New Zealand mud snail are the focus of a three-year, $599,748 research project CSU begins this month, which is set to investigate what allows these species to thrive away from their natural habitat.

Invasive species cause environmental damage and losses totaling over $120 billion per year, according to an Environmental News press release.

The money is part of a $3.6 million Environmental Protection Agency grant given to six universities to determine the ecological effects of climate change, land use and the subsequent impact on invasive species. The project at CSU will focus on effects of climate change.

“Invasive species have a major economic impact on the United States and we need to know whether a changing climate will increase this impact,” said George Gray, assistant administrator for EPA’s Office of Research and Development, in the press release.

Poff’s request for the grant, which was selected from more than 100 other proposals, focused on two species that pose a particular threat to river ecosystems in the western U.S.: the New Zealand mud snail and the saltcedar.

As the primary investigator for the project, Poff said these two species were selected out of a vast number of invasive organisms for a variety of reasons:

First, Poff said the research team wanted to examine two vastly different species. The snail is a small, aquatic creature, which produces multiple generations per year. The saltcedar, on the other hand, is a large terrestrial species that takes many years to reproduce.

Second, each species poses a continuing threat to the ecosystems it invades:

The mud snail can reach numbers over 800,000 per square meter within a few years. It feeds on algae, and if the algae disappear, so do consumers high on the food chain, such as fish.

The saltcedar displaces native cottonwoods, disrupts migratory bird roosting, increases fire danger and alters the salinity and water level of river ecosystems.

Poff said his goal was to select species that would illustrate the dynamics of small or large species, terrestrial or aquatic, rapidly reproducing or slowly reproducing.

“We want a model that could be used for all species,” Poff said.

Finally, and most relevant to the climate change issue, each of these species seem to be limited by cold winters.

While both organisms are found somewhat abundantly in the lower, western states, they have yet to make their way to much of the colder Northwest.

The effect that a warming climate may have on the ranges of the snails and the cedars is the major component of CSU’s research.

Poff said the project will be a joint effort between CSU faculty, geological survey officials, the U.S. Forest Service, the Bureau of Reclamation and staff members from other universities.

Poff’s study focuses on a mere 25,000 square kilometers — just a fraction of Colorado’s land. His is unique because most studies focus on much larger areas.

“One [previous] model predicts the mud snail could occur everywhere across the United States,” Poff said. “We want to know what the local conditions are — which will be favorable and what won’t.”

Poff said the research will use three types of models to understand how fast and where these species could spread if climate change continues as expected:

The team will use a Global Circulation Model to predict future climate around the world.

Statistical predicted precipitation averages will help develop an expected annual precipitation model for the river systems they will be studying.

Hydraulic models will take into account the current flow of rivers and changes in future precipitation to determine what the annual flood cycle (from snowmelt and rain) could look like for western rivers.

Ecological models will help the team examine how altered flood cycles will impact snail and saltcedar survival rates.

“CSU has expertise in all these areas that allows for successful collaboration,” Poff said. “Other schools aren’t able to do that.”

Poff said potential new habitats for both species must be conducive to their survival. To flourish in new conditions, species must have a low mortality rate. Natural events, such as floods in river systems, cause deaths and create unfavorable conditions.

“The question is,” Poff said, “can they persist? Can they survive?”

While many natural species in the river systems can adapt to adverse conditions, the invasive organisms sometimes do not.

For example, the small mud snail does not have the ability to hold onto the riverbed, and its small size makes it vulnerable to being washed out of the river during flooding.

On the other hand, the native cottonwood has evolved to release its seeds during the annual snowmelt flooding, making spread and reproduction easier, and holding invasive trees, such as the saltcedar, at bay.

Poff said if the annual flood cycle is altered due to climate change, the snails could have an easier time in rivers that traditionally have high floodwater, and the cottonwoods could be less able to compete with the saltcedar.

To calculate the likelihood of this spread occurring, Poff will compare his precipitation and hydraulic models to develop a master model of where species could spread.

Using large-scale techniques in small areas, Poff plans to determine local environmental effects from the invasive species.

“We’re going from few square meter snail habitat to global circulation models,” Poff said.

“It’s interesting research because it’s all about the future,” Poff said.

Staff writer Jim Sojourner can be reached at

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