Search for Rare R.I. Salamander Happens in the Dark
October 22, 2020
RICHMOND, R.I. — After dark at a well-hidden vernal pool, Peter Paton shined his flashlight back and forth at the moss-covered ground around the nearly-dry pond basin. He was searching for marbled salamanders, the only autumn-breeding salamander in New England, and one that is seldom seen except on rainy fall evenings. It didn’t take him long to spot one.
“I got one,” he called out. “Over here.”
Marbled salamanders, which grow to about 3.5-4.25 inches, are the second-largest salamander in the region — after only the spotted salamander — and their attractive black-and-white patterning makes them unmistakable. The one Paton found, a male, was on his way out of the pond basin, indicating that the animal had completed his mating duties and was headed to the forest to spend the winter underground.
Female salamanders were likely hidden in the sphagnum moss around the pond, where they remain for a month or more to guard their eggs until rain fills the pond and the eggs are protected from predators and the elements. The eggs hatch within days after being covered in water, and the larvae overwinter in the pond.
Paton, a professor of natural resources science at the University of Rhode Island, was confident of finding marbled salamanders at the Richmond site, since it was a place he studied and monitored in 2000 and 2001, when he and colleagues conducted an amphibian survey of 137 vernal pools around the state. Marbled salamanders were found in just four of the pools, however, making it one of the rarest pond-breeding amphibians in the region.
Previous efforts in the 1980s and ’90s by Chris Raithel, a wildlife biologist at the Rhode Island Department of Environmental Management, documented as many as 50 marbled salamander breeding sites in the state, mostly in Kent and Washington counties. There are no records from Bristol County or from areas adjacent to Narragansett Bay and few from the Blackstone Valley.
“The present localized distribution of marbled salamanders in Rhode Island may be related to habitat fragmentation and patch isolation,” Raithel wrote in his 2019 book Amphibians of Rhode Island. “If this effect is real, the species is secure only in the larger contiguous habitats of southern and western Rhode Island, and additional range retraction should be evident to future generations.”
Marbled salamanders require a very specific habitat for breeding: ponds that are surrounded by sphagnum moss and dry up in the summer, keeping fish and large dragonfly larvae from inhabiting the pond and preying on the salamander larvae.
“They tend to like relatively small ponds, and there aren’t many sites available that fill their habitat requirements,” Paton said.
In addition to habitat fragmentation, road mortality is also a significant concern for the species, because they are often crushed by vehicles as the adults cross roads to reach their breeding ponds or as juveniles disperse to find territories.
On the other hand, Paton said it’s possible that the changing environmental conditions associated with the warming climate may make southern New England more favorable to marbled salamanders in the future. Their current range extends as far south as northern Florida and eastern Texas, and populations in warmer climates tend to be considerably larger than those in Rhode Island.
“They aren’t very tolerant of the cold, so we’re at the northern limits of their range,” Paton said. “The larvae don’t grow much in the winter because it’s too cold, but once wood frogs arrive to breed in early spring, the salamander larvae feed on the frog tadpoles as their main fuel source to undergo metamorphosis.”
After metamorphosis, the salamanders leave their ponds and spend the rest of their lives in the forest, except for brief breeding periods each fall.
Despite how few marbled salamander breeding sites were found during the last amphibian survey, a recent graduate student at the University of Massachusetts Boston thinks a new survey method may detect the salamanders more effectively than traditional sampling methods.
Jack He, who graduated in May, used eDNA — environmental DNA collected from water or soil — to detect the presence of marbled salamanders even when the animals could not be seen.
“Everything sheds DNA in one form or another, like from skin cells or blood, and they release it into the environment,” He said. “Ideally, we can collect water or soil samples containing those cells and extract that DNA and sequence it to determine what species are present.”
He detected marbled salamander DNA in a number of water and soil samples from vernal pools in western Massachusetts. He calls it a less labor-intensive method of determining if the salamanders are present at a site than using dipnets to capture larvae in the spring, which is how Paton conducted his survey.
“I’ve done dipnet studies and compared them to eDNA, and I found that eDNA was a bit more effective,” He said.
Paton, however, isn’t convinced.
“My impression is that larvae are relatively easy to find, but I could be biased,” he said. “Maybe they’re in there and I missed them a lot. But however you do it, I suspect that marbled salamanders are still fairly rare in Rhode Island.”
Rhode Island resident and author Todd McLeish runs a wildlife blog.