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Waterfall and their inhabitants

Waterfall and their inhabitants – thinking of Cherrapunji

In 1991 I spent two months of my sabbatical with my Indian wife at NEHU (the North East Hill University) in Shillong / Meghalaya. From there we once made a trip to Cherrapunji, also known as Sohra, to take a look at the majestic Nohkalikai Waterfall with its height of around 350 m.

There’s no shortage of water in that part of India and Cherrapunji with an annual average of 12,000 mm rain is considered one of the rainiest places on Earth. When we visited there, the sun was mostly shining and I asked a local person if there were perhaps frogs in, under, or behind the fall. And the man replied that, yes, occasionally they’d find frogs that seemed to have come down in the water of the waterfall.

Imagine living in, under, or behind such a torrentuous and constant flow of water, in continual danger of being flushed away or crushed, unable to return to where you used to live: you need some way of securing yourself, some safety net, some device to cling to the substrate, don’t you? And that’s exactly why I find the habitat of waterfalls so fascinating. Research into who and what is eking out a life in waterfalls is scarce, but what we do know is indeed remarkable. Nohkalikai, in my opinion, would still hold many surprises of organisms uniquely adapted to a life in one of toughest environments on Earth.

There are frogs associated with waterfalls and some, occurring in Vietnam and China, have been studied. Species of the genus Amolops, for instance, are not exactly large, but unsurprisingly possess rather big toepads. Their very flat and fishlike tadpoles, however, sport some amazing adaptations in the shape of a ventral sucker disc that allows them to stick to the rocks, thereby resisting to be flushed away. They survive in this habitat by scraping off algae that form a growth on the slippery rocks. Another vertebrate with adaptations to survive in the water of a waterfall (but this time in Hawaiian waterfalls) is a fish of the goby family, known as the Nopili climbing goby Sicyopterus stimpsoni. This little waterfall denizen also possesses a sucker, which is located on the ventral side of its abdomen and the result of a fusion of the two pelvic fins. It therefore is of a different origin from that of the tadpole sucker mentioned above; it’s not a homologous but an analogous organ. However, to make doubly sure that it won’t lose its foothold (sorry, better “tummyhold”) the goby uses its mouth as an additional sucker. Like the tadpoles, this fish, too, feeds on the algal growth on the waterfall’s rocks.

Where there is a source of food and shelter, one would expect insects to be present as well. And there are indeed many aquatic species that have become adapted to survive in the waterfall habitat. Such insects are usually small with delicate bodies and capable of protecting themselves by sheltering in rock crevices or clinging to the algae on the rocks. For that purpose they often have grasping legs that end in toes with hooks and claws. Some representatives are riffle beetles of the family Elmidae, the larvae of some may-, stone-, and caddisflies and the very special larvae of net winged midges, the Blephariceridae. The latter not just have one sucker on their ventral side like the tadpoles or two like the climbing goby, but six! How these larvae (and some of the mayfly Baetis spp.) withstand the power of the water is astonishing and related to the tortoise-like shape of the blepharocerid larvae. The forces that the sucker organs are able to generate have apparently not yet been measured, but I once carried out observations on the ability of Simocephalus waterfles to adhere to the aquarium glass. They are not inhabitants of waterfalls but use sucking devices as not to be displaced by strong currents. To prevent being dislodged by strong water currents from stones they are resting on, the marine lumpsucker fish Cyclopterus spp. also use a ventral sucker made of a pair of modified pelvic fins.

That algae and diatoms can grow on the rocks under a waterfall is perhaps not terribly surprising, but there is even an angiosperm plant known to survive in waterfalls. It’s a Podostemon species and not being able to find attachments for its roots on the slippery rocks, it uses chemical adhesives. I bet there would be some tiny flat snails as well. Now that would be something to study the chemical adhesives of and copy them in the lab. I think there’d be millions to be made, because as we all know, glue does not stick well in flowing water. But Podostemon and possibly tiny snails have found a way.

© Dr V.B. Meyer-Rochow and, 2019.
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