Little Cayman’s tiny snails in the spotlight

A group of the rare snails.
A group of the rare snails.

A tiny population of snails found only in Little Cayman may be making a comeback.

Recently, researchers from the Department of Environment found that the numbers of these rare snails once on the brink of extinction have risen significantly since researchers recorded fewer than 100 of them in the mid-1970s.

In the September/October issue of the Department of Environment’s Flicker bulletin, Fred Burton wrote about the tiny creatures that, though small in size, represent a unique element of Little Cayman’s fragile ecosystem.

“There are places in the west of Little Cayman where you can easily wander off the road into a habitat that is hard to find anywhere else in our islands. The ground is smooth, flat rock with thin layers of soil here and there. The plants are low and spaced apart, so you can move around freely,” writes Mr. Burton.

Describing how the small trees and shrubs are festooned with land snails, in the article he notes that on these limestone flats the ground is ornamented with clusters of their white dead shells. Of interest, among the fat inch-long shells that are everywhere, an occasional much smaller and thinner shell can be found.

“This is the shell of Little Cayman’s unique Cerion nanus snail, believed to be one of the most endangered snails on Earth,” he wrote.

“Their shells can be found over all the limestone flats throughout western Little Cayman, but live ones have long been known to be restricted to a few tiny colonies close to the Spot

Bay Road. Once they were obviously far more widespread. Whatever happened?”
He noted that the area also contains occasional lumps of very old, weathered coral which are out of place.

“According to DoE’s marine biologists Croy McCoy and Philippe Bush, these are probably pieces of the Boulder Brain Coral, Colpophyllia natans, a species found on the slopes and tops of reefs,” wrote Mr. Burton, adding that the coral pieces are modern corals from the sea, not fossils, and can only have ended up where they were in a tumultuous storm powerful enough to rip the corals off the reef and the coastline, throw them up to 800 yards inland and on to land 8 feet or more above sea level.

“All that surging seawater would be immediate death for any land snails in the way,” continued Mr. Burton.

“So maybe that is why the last living Cerion nanus colonies off the Spot Bay road are all in areas protected from storm surges by a 20-foot ridge of high land. The bigger land snails seem to be tougher and more mobile, and may soon have recolonized the storm-shocked landscape closer to the sea. Cerion nanus seems to be having a harder time.”

He noted that recent surveys by the Terrestrial Resources Unit suggest that despite this, Cerion nanus is recovering, with numbers far above those recorded by Mike Hounsome and Dick Askew during the Cambridge University/Cayman Islands Government biological expedition to Little Cayman in 1975. At that time the researchers estimated the population of Cerion nanus to number about 88 individual snails – which Mr. Burton observes is perilously close to extinction.

After that, their numbers appear to have been growing, as in January 2012, Dr. Mat Cottam counted 266 live snails, noting there were also more uncounted ones hiding under rocks.

“In a short visit by myself in June this year, the estimate shot much higher again, with a density suggesting some 5,000 of these unique snails may now be alive,” wrote Mr. Burton.

“In August, I returned to Little Cayman, and with TRU’s Jessica Harvey, discovered two new colonies of living Cerion nanus in the same ridge-protected area, and another small cluster now on the oceanside of the ridge,” he continued.

“Are the surviving colonies starting to spread? This is all great news for Little Cayman’s tiny, unique and critically endangered land snail.”

Mr. Burton stated the Department of Environment plans to develop a Species Conservation Plan for Cerion nanus this year, under the framework of the National Conservation Law.