Waterfall is a word we often associate with greenery, a respite from the summer heat, vacations, and lots of photographs. How many times do we think of the word ‘snail’ when talking about waterfalls? Never! But several waterfalls in the Western Ghats are home to tiny snails called Cremnoconchus. The word is derived from Greek and literally translates to ‘cliff shells’ – they are found on the walls of waterfalls and hence their name.
Cremnoconchus belongs to a family named Littorinidae. Interestingly, Littorinids—or Periwinkles, as they are commonly referred to—are marine snails. All other members of this family reside in the salty waters of seas, barring Cremnoconchus, which seems to prefer the sweet water of waterfalls. Scientific literature says, as of today, Cremnoconchus is found only in certain regions of the Western Ghats biodiversity hotspot. Three species are present in Maharashtra and have been described by the British in the 19th century. ATREE, Bengaluru, in collaboration with scientists from Natural History Museum, London, described six new species, all residing in Karnataka, about 120 years later. With that, the total number of species under this genus has increased to nine.
Ticking the clock backwards to shed light on their evolutionary history reveals that this genus had marine ancestors as well. They diverged from their marine sisters, and with receding sea levels, moved from the sea into the freshwater realm. Their origin dates back to more than 100 million years; thus, they are believed to be of Gondwanan origin. In other words, this genus was present when the super-continent of Gondwanaland still existed. Despite having a history this ancient, Cremnoconchus has managed to colonise waterfalls only in westward-flowing streams. As is said, it was moving at a snail’s pace!
Each waterfall that houses Cremnoconchus is associated with a distinct species. The only exceptions are Hulikal Falls in Hulikal Ghats and Kadambi Falls in Kudremukha – these falls have two different species each, occurring together.
All species of Cremnoconchus are grazers and detritivores: they feed on algae and decaying organic matter. They use a series of teeth called radula to scrape food items from the rock surface. Cremnoconchus rests and feeds inside small crevices or secluded areas of the rock during the monsoon and post-monsoon seasons, to avoid being washed away by the water flow. Also, it moves towards the edge of the waterfall, where only water spray or a thin stream of water is present. During summers, groups comprising of about 100 adult and juvenile individuals congregate and aestivate in shaded regions of the rock or inside crevices closer to the waterfall, to reduce desiccation.
Snail shells are entirely built with calcium carbonate and contain an external protein coating. Studies suggest that snails obtain their share of calcium from plants, which act as calcium pumps, and some of it also from the rocks that form the soil in which they thrive. Additionally, snails can also take up calcium from leaf litter, which is the primary constituent of their diet, and from the logs in which they seek shelter. Owing to varying calcium contents in plants and soil, assemblages of snail species differ in different areas. As part of the food web that exists in nature, snails act as excellent reservoirs of calcium for their predators. Though not much has been studied specifically about the species found in the Indian subcontinent, global studies suggest that snails have a number of natural predators: these include turtles, salamanders, birds etc., and a number of insects like beetles. The predators either feed on snail flesh (which also contains calcium) or directly on snail shells, which are richer sources.
Lack of calcium in an environment will have a direct impact on the snails it harbours. The most common reason for extensive loss of calcium in soil is acid rain. With snail populations dwindling, its predators will also be impacted: for starters, their source of nutrition will be lost. Secondly, the calcium they get from snails helps in forming the rigid shells of the eggs they lay; in the absence of adequate calcium, their egg shells become brittle and undernourished, and highly susceptible to damage. In one instance, it has been observed that scarce quantities of calcium in the immediate environment led to a type of cannibalism – adult snails in the population were seen to devour the shells of most young ones, at least partially. As is known, shells are indispensable when it comes to self-defence and a lack of the same leaves the younger snails highly vulnerable to physical damage and provides easy access to predators. This means that entire populations of snails could be wiped out without the required quantities of calcium in their surroundings, and this will in turn affect the other species thriving in that area, resulting in an irreparable ecological imbalance.
Several species of Cremnoconchus are found either on roadside waterfalls or in those which attract a large number of tourists, such as Hanuman Gundi (type-locality of C. hanumani), Koodlu Thirtha, etc. Some of these waterfalls see an influx of many thousands of people annually. Cremnoconchus sp. is extremely vulnerable to extinction due to its small size, the limited extent of its vagility (ability to move about or migrate), specific habitat requirements, endemism, and high dependence on water (moisture in general). Threats such as upstream pollution, habitat fragmentation, mining, construction of dams, and forest loss adjoining waterfalls, are harmful for them. But the most significant impact is due to extreme tourism-related activities and the unimaginable quantities of solid waste that come with it. Post-monsoon, a period when tourist footfall is the highest—leading to maximum disturbance to their habitat—also coincides with the period of their maximum activity. Thus, the disturbance has a detrimental effect and leads to added pressure on the snails.
Given the above, immediate steps should be taken towards the conservation of these so-called “non-charismatic” but iconic species of the freshwater habitats of the Western Ghats. Not only are snails important sources of calcium, but they are also critical indicators of the health of the environment. A decrease in their population means that the overall health of that habitat is deteriorating. It’s a no-brainer to guess that the deterioration will be disastrous for all the animals and plants living there, and not confined to a single species. In summary, given their narrow range, habitat specificity, threats due to anthropogenic activities especially tourism, and their unique evolutionary history, prompt action is needed towards devising better conservation plans. A stricter pollution law, effluent treatment before release into water bodies to prevent downstream pollution, restoration of the unique habitats where snails occur, and minimising human-related activities around them, will help in restoring the snail population.
So the next time you visit a waterfall in the Western Ghats, do keep an eye out for these tiny organisms, which silently provide us with invaluable services. Ensure that you do not litter the area or disturb the habitat. Always reduce, recycle, and reuse, and be part of the reason these snails survive longer!