Underwater sounds

We are all familiar with birdsong, the chirruping of cicadas and grasshoppers, and the high-pitched sonar of bats (at, least, we are when very young, before the need for bat detectors that allow us to hear them when our hearing is less acute). There are other noises we all recognise in our terrestrial world, too, like the sound of the wind blowing through trees, the buzzing of insect flight, or the calls of foxes and other mammals.

Much less familiar are sounds from under water, although there are many recordings of the calls of whales that allow communication over large distances. We find whale “songs” haunting and there are hours of these on the internet. But what of sounds from ponds and other small water bodies? There’s the croaking of frogs at some times of year, although that is really part of the terrestrial realm, since the sound is transmitted through the air. Unknown to most of us, ponds are quite noisy, as I discovered in a wonderful radio programme about “ghost ponds” broadcast on the BBC [1].

In Norfolk, pits were dug to extract marl that was applied to fields as a fertiliser and soil improver, being relatively rich in calcium. The excavated pits filled with water to form ponds and almost every field had one, although they became neglected, or filled in over time, as agricultural practices changed – thus the ghosts referred to in the programme. A project to rehabilitate and research marl ponds has been supervised by Professor Carl Sayer of UCL [2, and see above] and he explained in the BBC broadcast that cleaned-out marl ponds form wonderful habitats for freshwater and amphibious animals, and for aquatic plants. It was such a joy to listen to Carl as he explained the project with his expertise and characteristic enthusiasm.

I already knew about the project from an earlier visit to Norfolk [3], but was surprised that the BBC programme started with commentary from Jack Greenhalgh of Bristol University, who described the sounds made by organisms living in the marl ponds, with soundtracks made using hydrophones. Intrigued, I looked up one of Jack’s websites that has recordings from a wide range of marine and freshwater habitats [4]. It came as no surprise that water bugs make a lot of noise, as the adults are able to fly and calls in the terrestrial world work even better underwater. More of a surprise was the sound of a coral reef and that of plants respiring.

It all added to the fascination of the story that Carl told and reminded me of why I can become so absorbed by natural history. So much of our lives is dedicated to anthropocentricity and it is humbling to discover new things about the natural world and realise how little we know. 

[1] https://www.bbc.co.uk/programmes/m000nlzk

[2] https://ghostponds.wordpress.com/

[3] https://rwotton.blogspot.com/2013/06/watching-azure-damsels.html

[4] https://soundcloud.com/wildaudiojack