From the world’s biggest subterranean fish to a cricket that communicates through vibration—India’s caves are full of treasures waiting to be discovered. This is finally beginning to happen as scientists realise these isolated systems can not only lead to the discovery of exciting new species but throw light on the evolution of humans and perhaps, even offer a model to study and combat climate change.
For speleology—the study and exploration of caves— is now impacting branches of science such as biology, anthropology, geology and hydrology. In India, nine researchers, led by senior research biologist Dhanusha Kawalkar of the Tamil Nadu-based Salim Ali Centre for Ornithology and Natural History, came together in September to form the Speleological Association of India.
Their expertise ranges from geology to biology but they are united in their zeal to conserve and document caves. And India has thousands of them, be it in Meghalaya, Madhya Pradesh, Chhattisgarh, Kerala or the Andamans. Each has its own microclimate, the dark, twisted passageways home to a host of rare and endemic species of fauna—fragile ecosystems now facing threats for reasons as varied as poaching and a changing climate.
Rajeev Raghavan, assistant professor at the Kerala University of Fisheries and Ocean Studies and South Asia chair, IUCN SSC Freshwater Fish Specialist Group, describes this as a rather new research field. “There is a big difference in working in micro and surface environments. Say, when someone carries out research on lake or river fish, you know where you need to travel to, it’s easy to go back repeatedly. But caves are not easily accessible. They require months of exploration. The funding required is different. But the field is picking up slowly,” says Raghavan, who specialises in micro ecosystems and has been studying the caves and subterranean aquifers of Kerala.
He says there are three key regions where cave fish are found in large numbers—China, Mexico and the US. India comes next. However, each of the top three countries has had a decades-long head start in studying cave ecosystems and the fish species that dwell within. They have now begun to look at the applied aspect of speleology. “In India, we have just started and are in the first stage of documentation. But hopefully we will get there,” he says.
The number of collaborations between scientists and explorers from India and abroad on annual expeditions to study caves is on the rise. “Caving in the Abode of the Clouds” is, for instance, an ongoing project that is attempting to systematically explore the caves of Meghalaya. It’s a partnership between Indian, European, Middle Eastern and American universities and independent researchers, with over 519km of cave passages having been surveyed since 1992.
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Brian Dermot Kharpran Daly, 75, co-founder of the Meghalaya Adventurers’ Association formed in 1992, has been associated with the project since its inception—and continues to be part of its many discoveries. He believes caves are one of the most significant scientific resources, where evidence of all life is hidden within, waiting to be deciphered. “Studying the forms of life and their adaptation to the conditions will give you an indication of evolution,” says Daly, who has identified over 1,700 caves in Meghalaya since 1993 and mapped around 1,000 of them. “Geologists can study the rock structures, some dating back to millions of years. Hydrologists study the drainage of water, its origin and direction of the flow. For anthropologists, caves hold the key to the evolution of man. After all, evidence of Neanderthal man and hominids were all found in caves. Hence caves cater to all forms of science.”
He was part of a 2019 research trip led by Daniel Harries, a biologist from the Heriot-Watt University in Scotland. Within a limestone cave in a remote forested part of Jaintia Hills, the team found a nearly-blind species of fish, similar to the Golden Mahseer, which turned out to be the world’s biggest subterranean fish. Compared to the average size of 8.5cm seen in the 250 known species of subterranean fish, this one measured 40cm. Raghavan is undertaking genetic and morphological studies on the fish, which remains unnamed.
Of late, the discoveries have been coming thick and fast. In 2021, yet another limestone cave in Meghalaya—Mawsmai—led researchers to a micro snail species, Georissa mawsmaiensis. These were found by Nipu Kumar Das and N.A. Aravind of the Ashoka Trust for Research in Ecology and the Environment, Bengaluru, nearly 175 years after the last such genus was discovered in the area.
In the same year, thousands of kilometres away, in the Kurra caves of the Lailunga block in Chhattisgarh’s Raigarh district, a unique species of small, sightless, and completely deaf crickets was discovered by a team from Panjab University led by Ranjana Jaiswara of the zoology department. It was named Arachnomimus Jayanti after Chhattisgarh-based scientist Jayant Biswas of the National Cave Research and Protection Organisation (NCRPO). “Crickets are noticeable for their loud calls, especially at night. Interestingly, males of the new Jayanti subgenus cannot produce sound and their females don’t have ears. The crickets were found on the walls of the Kurra caves, which don’t have light inside. They may be communicating by beating their abdomen or any other body part on the cave walls,” notes an article in The Indian Express from the time.
Raghavan describes the species found in subterranean ecosystems as evolutionary distinct organisms. “These have been very isolated systems for millennia. Environmental parameters have remained unchanged as the creatures within have not been exposed to harsh conditions or other anthropogenic factors. Any small change in light or temperature affects them deeply,” he says. In the course of his study, for instance, he has collected crustaceans and fish from subterranean ecosystems in Kerala which try to avoid light when they are brought out. “There is a big difference in the morphology and physiology of these animals. Most are blind as they live in the dark. However, in order to circumvent the environment, they have developed powerful senses,” explains Raghavan.
They have acquired shapes that allow them to pass through crevices and aquifers. Some subterranean fish can be found in wells in Kerala. They don’t live there, they are just passing through the laterite rocks. “Meghalaya has more expansive limestone caves, as opposed to Kerala’s smaller laterite ones. However, in all of the regions, the organisms exhibit either very advanced or reductive characters—no fins on top to enable them to move through small spaces, heightened senses but no vision,” Raghavan notes. Biswas adds that albinism is yet another characteristic of these organisms. While we have melanin to protect us from the harsh sunlight, such pigments are not needed in the dark caves.
Link to climate change
Besides understanding the unique biodiversity, one of the most significant applications of cave research can be seen in the understanding of climate change. Daly cites the example of Ashish Sinha, professor of earth sciences at California State University Dominguez Hills, US. His field of research is climate change with a particular focus on high-fidelity reconstruction of precipitation patterns in tropical and monsoonal locations over the past several millennia.
“He is studying this through sediments in stalagmites found in caves. I took him to caves such as Krem Mawmluh in Meghalaya (in 2018), where we took samples of stalagmites dating back to 40,000 years or so,” he says. Following isotropic analysis, the stalagmites told a story of a 200-year-old mega drought in the Holocene era that impacted such human civilisations as those in the Indus Valley. “The chemical signature embedded in the rock was very distinct, thus prompting the International Commission on Stratigraphy to name the period, from 4,200 years ago to the present, as the Meghalayan Age,” says Daly. An understanding of this paleoclimate will help trace the key moments that had an impact on a region’s climatic condition and may even help equip us to combat climate change better.
According to Climate Change Going Deep: The Effects Of Global Climatic Alterations On Cave Ecosystems, a paper published in The Anthropocene Review, 2019, caves represent one of the most informative systems for the study of climate change across its biotic and abiotic components. This holds true for multiple reasons, notes the paper: They are semi-closed systems that are extensively replicated across the earth; they are buffered from external variations and generally characterised by a remarkable thermal stability, especially in temperate areas; temperatures inside caves correlate highly with mean annual temperatures on the surface; and subterranean organisms have evolved a suite of morphological and physiological adaptations to thrive under the peculiar environmental conditions found in caves, which are often convergent even across phylogenetically distant groups. “However, a lack of synthesis on this topic is possibly holding back the establishment of caves as standard models for the study of the effects of climate change in the field,” state the authors of the study.
In a conversation with the Mongabay-India news service in April, Jaishri Sanwal Bhatt, a scientist from the geodynamics unit of the Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru, explained that stalagmites, which grow from the cave floor and are basically deposited layer by layer every year, end up preserving data from their environment during the time of formation. “If we can get people to see the science behind caves and its fragile ecology, it would motivate the local communities to conserve these caves instead of destroying them,” Bhatt said.
Poachers have, unfortunately, been ahead of scientists. Take the example of the edible-nest swiftlet, a species living in caves in the Andamans. Till some time ago, its nest, made of its own saliva, had many takers in countries like China, where it was made into a soup. In other parts, locals too feast on some species, like the bats found in the Singhanpur caves of Raigarh.
The threats are manifold, says Biswas, with even pollutants from the surrounding areas entering the water and threatening the very existence of some species. As part of his organisation, NCRPO, he has been trying to educate villagers about the key role Singhanpur bats play in the agrarian ecosystem—their droppings are high in phosphate, better than any other form of manure. Also, a single cave bat eats pests 1.5 times its body weight at night.
In Kerala, laterite mining for construction is wreaking havoc. “Most subterranean systems in the state lie in laterite zones from the north to the south. Not only are they being mined at a fast rate, a lot of groundwater extraction is also taking place. These are obvious threats to the ecosystem,” says Raghavan.
Time is running out.