Everglades pythons threaten adjacent ecosystems

An invasive Burmese Python on Her Nest in South Florida. PHOTO COURTESY JEMEEMA CARRIGAN, UNIVERSITY OF FLORIDA.

Saltwater may not be an effective barrier to halt the spread of invasive snakes in south Florida

By Summit Voice

SUMMIT COUNTY — Invasive Burmese pythons breeding in the Everglades may pose a threat to adjacent ecosystems and even nearby islands like the Florida Keys, according to U.S. Geological Survey scientists who recently tested the pythons for their tolerance to saltwater.

Resource managers had hoped that saltwater would block the spread of pythons from the Everglades, but the study showed the young snakes can withstand exposure to salt water long enough to potentially expand their range through ocean and estuarine environments.

The research was published in the latest issue of the Journal of Experimental Marine Biology and Ecology.

The pythons were released as unwanted pets. They can grow up to 20-feet long in their native Asian habitat. In the Everglades, they’ve been eating gray squirrels, possums, black rats, house wrens, and even bobcats and white-tailed deer. The National Park Service is also concerned that the snakes may be preying on species of concern, including native mangrove fox squirrels and wood storks. The agency estimates that there are now thousands of pythons living in the Everglades.

“Because reptiles, in general, have poor salinity tolerance, it was hoped that salt water would naturally hinder pythons’ ability to expand their range beyond the Everglades,” Hart said.” Unfortunately, our results suggest salt water alone cannot act as a reliable barrier to the Everglades python population.”

Burmese pythons have been found in brackish margins of the Everglades, but there was no information about how long the snakes could persist in saline environments.

The issue of salinity tolerance is critical for understanding the risks of the giant constrictors spreading beyond the Everglades, given the Everglades location on the southernmost end of the South Florida peninsula.

“The fact that this study has ruled out one of the most hoped-for forms of physical barriers, salt water, as preventing the spread of invasive pythons in Florida puts even more onus on human action to prevent the spread of these damaging reptiles,” said USGS director Marcia McNutt. “This study demonstrates the distinct possibility that pythons could spread to new suitable habitats one estuary at a time.”

In the lab, researchers tested how long hatchling pythons could survive with only salt water to drink. They found that, when given access only to water with salinity levels equivalent to full marine water, hatchling pythons straight out of their eggs lived about a month. At salinity levels comparable with estuaries, the hatchlings survived about five months.

The USGS research showed that varying salinity levels did affect the snakes, as reflected in significant survival differences between pythons exposed to freshwater, marine, and estuarine salinities in the lab.

Because hatchlings are considered the most vulnerable stage of the python’s life, it’s likely that adult snakes could persist even longer in saltwater environments, Hart and her colleagues noted.

By comparison, pythons in the study displayed a saltwater tolerance level near that of the native mangrove snake, a salinity-tolerant native snake found in high-salinity environments in and around the Everglades.

Although the study didn’t account for the effect that access to food in saltwater environments would have on survival, lab conditions were designed to provide a conservative estimate of snake tolerance to salinity, by not allowing for the possibility that snakes could access freshwater from rain.

The study, Experimentally derived salinity tolerance of hatchling Burmese pythons (Python molurus bivattatus) from the Everglades, Florida (USA), is authored by USGS scientists Kristen M. Hart, Pamela J. Schofield, and Denise R. Gregoire. The article can be downloaded.


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