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Gobabeb Research & Training Centre

Desert Snails

The Namib Sand Sea, a majestic yet inhospitable body of dunes, flowing over some three million hectares, engulfs the land with its parched grasp. What decades of research, documentation and observation on the Namib Desert

has told us, however, is that it is anything but inhospitable - at least for the countless desert-adapted organisms that grace its scenic grandeur.

DuneLandscape

Countless creatures have evolved to contently inhabit this otherworldly environment, such as burrow-digging geckos, scorpions and spiders, or the beetles, which conjure up inventive ways to exploit the regular fog to obtain necessary moisture. These organisms and many others have captivated generations of curious minds. Often one can physically see and therefore logically understand the extraordinary evolutionary adaptations bestowed upon these creatures, which enable them to survive in hyper-arid conditions. Whilst one may be able to deduce that many of these desert-dwelling inhabitants belong to this environment, merely by observing physical traits, beneath the surface lie some rather unexpected, logic-defying residents - snails.

Terrestrial snails are present in many of the world’s deserts, and the Namib is of no exception. Snails are often associated with wet areas; so learning that they exist here may come as a surprise. Parts of the Namib seldom see rainfall and some years may go by without any at all. Incredibly some snails have evolved to exploit infrequent rainfall, lying dormant for months or even years at a time and then surfacing shortly after heavy rainfall or on damp, foggy nights and mornings at certain times of the year.

Trigonephrus haughtoni-4

Certain snails have been observed to bury themselves several metres below ground surface, entering a state of dormancy. When the snails are dormant, water loss is dramatically reduced to the point where some species can survive for several years without moisture. Upon rare desert rainfall seeping into the sandy soil, snails can emerge for a limited time to feed and reproduce before cosily burying themselves beneath the surface once again.

There have been reports of snails emerging from their subterranean dwellings in droves, making walking across the surface without crushing their shells impossible, only for them all to completely disappear ten minutes later at sunrise, with even digging not revealing the slightest evidence of the prior mass-congregation. A snail from an arid region of northern Africa, originally thought dead, was once glued to a plaque in the British Natural History Museum, only for it to emerge from it’s shell four years later after water had been applied to the plaque. For creatures that are often overlooked or disregarded, they are certainly capable of some truly incredible feats.

At Gobabeb, a scientific research station in the central Namib Desert, several snail shells have been lying in and around a small fenced-off enclosure on a remote interdune area for many years. The shells have baffled many-a-scientist, their origin a mystery. Several of these shells were recently sent to an expert in South Africa, Dr Willem Sirgel, who identified them as Trigonephrus haughtoni, a relatively large terrestrial species of snail, which has been previously found and studied in the southern Namib but never in the Gobabeb area. “The fact that no living snails have been seen [at Gobabeb] is not so strange”, explains Dr Sirgel. “Trigonephrus spends most of its life underground [and] I can only come to the conclusion that if there are shells, there must be some snails at least nearby”. Dr Sirgel proposes that the snail shells in and around the enclosure plot may be a result of birds preying on them and then carrying them there, perching on the fence, the only high perch point on the otherwise barren interdune, and then discarding the shells after having consumed the contents. Has the mysterious origin of snail shells around Gobabeb’s enclosure plot finally been solved?

Dune Interdune Landscape

Trigonephrus haughtoni-6

The shell of a Trigonephrus haughtoni.

Trigonephrus haughtoni-3

An empty Trigonephrus haughtoni shell collects sand. Wasps, bees and spiders have been observed utilising empty, sand-collecting Trigonephrus shells to construct stable nest cavities.

 Throughout history, the Namib has cycled through wetter and drier climatic periods, which leads to another theory - that the snail shells are thousands of years old and Trigonephrus species do not occur in the Gobabeb area anymore. Present-day rainfall patterns across the Namib might lead to Trigonephrus preferentially occurring in the southern but not the central Namib. Deep in to the Namib Sand Sea there are areas known as paeleo-lakes, which once held significant volumes of water. Stone Age tools have been found at these ancient lakebeds, now completely dry and inhospitable to man, as well as calcified stem casts of Phragmites - common reeds that occur in areas where freshwater is present. Stones show the unmistakable signs of being carried and shaped by water. Ancient animal tracks also exist in a remote area of the Sand Sea. The animals wandered across the mud, which then hardened, preserving their spoor for thousands of years. Shells of freshwater snails dating back to around 13,000 years have also been found at these sites. It is possible that the shells found at Gobabeb are just as old, if not older.

An archaeological excavation of a cave in the southern Namib revealed charred Trigonephrus haughtoni shell remains - the snails had been collected, cooked, and presumably eaten by hunter-gathers in the last two millennia A.D. The archaeologists state that the palatability of the snails is, however, unfortunately unknown.

This is an extract from the full article Unexpected Inhabitants written and photographed by Oliver Halsey.

 

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