Not only do pythons seem to be getting more and more comfortable in the Florida Everglades, including Everglades National Park, but they don't seem to mind salt water too much, according to a study of the reptiles.

The study, which appears in the latest issue of the Journal of Experimental Marine Biology and Ecology, demonstrates that "invasive Burmese python hatchlings from the Florida Everglades can withstand exposure to salt water long enough to potentially expand their range through ocean and estuarine environments," according to a USGS release.

Kristen Hart, a USGS research ecologist and lead author of the study, says the results show that pythons might be able to survive in marine and estuarine environments such as bays, inlets and open seas. And she adds that the study raises concerns that the invasive snakes might invade nearby islands, such as the Florida Keys.

“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,” Ms. Hart said. "Unfortunately, our results suggest salt water alone cannot act as a reliable barrier to the Everglades python population.”

Before the study, Burmese pythons had been found in brackish margins of the Everglades, the expansive and predominantly freshwater wetland that is home to the only known wild-breeding population of Burmese pythons in the United States. Yet, no information was available to indicate 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," explained 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 demonstrated, however, 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. However, 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, the report's authors 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.