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I have a species that have evolved from their world's equivalent of deep (~3 kilometres deep) sea snails, specifically from they resemble the Scaly-Foot Gastrobpod. The Xeno-ocean is salty/has a significant concentration of conductors/electrolytes dissolved in the water (similar to our ocean).

I want their present day form to be

  1. land dwelling
  2. communicate biologically via radio signal
  3. with a body size roughly that of a dog (small or large)

They presently (i.e. on land) have another form of communication, a sort of radula clicking speech. But I'd like to understand how their deep sea ancestors communicated via radio wave, to form an idea how they communicate now.

I've read How to evolve biological radios?, which is helpful, but that obviously does not include the the fact that radio waves do not propagate well under water especially salty water.

That Wikipedia page (and others) doesn't go into enough detail for me to know if the sort of radio waves a species could evolve would attenuate after 10 mm or 10 meters. The lower part of that range is not useful for submarines, and the upper only for radio-controlled ones (which is seems to be the focus of articles on Wikipedia), but would be the difference between the species being able to use radio waves underwater or nor.

The reason I'm asking here, and not on Physics, is because even if there is a range of frequencies, if the antenna/transmitter required to communicate at various distances required unrealistic power levels or antenna bigger than is reasonable for a dog sized creature ( I mention that because some submarines use a very long trailing wire as an antenna, which violates the dog-sized requirement above ).

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  • $\begingroup$ If you are interested in short-range communications, the Wikipedia article radio controlled submarine may be of interest; money quote: "the lowest hobby bands, typically around 27MHz/40MHz, can penetrate several feet of water at short distances, typically less than 45 meters". On the other hand, for underwater communication radio is the almost often a much worse idea than acoustic waves. (And -1 for asking a set of benevolent strangers to do basic research for you.) $\endgroup$
    – AlexP
    May 19, 2021 at 14:00
  • $\begingroup$ @AlexP apologies for this, but is it really basic research? Look at one of the following lines form that article: Penetration at these frequencies is easier in fresh water, but are difficult to impossible in sea water. Is that implying that the 45 meters mark is only possible in fresh water or that it's possible at even larger distances outside of saltwater? There's also the possibility that those frequencies aren't possible at the scale of my creatures, which is also not obvious to me. $\endgroup$
    – AncientSwordRage
    May 19, 2021 at 14:38
  • $\begingroup$ @AlexP I've updated my question with more details that explain why that wikipedia page isn't a suitable answer $\endgroup$
    – AncientSwordRage
    May 19, 2021 at 15:37
  • $\begingroup$ The propagation of electromagnetic waves in sea water is a subject of very active research, for the obvious reasons. Putting "radio waves sea water" into Google will reveal a large number of articles. $\endgroup$
    – AlexP
    May 19, 2021 at 15:37
  • $\begingroup$ The frequencies of radio that penetrate water, require antenna size much longer than any dog. 2 to 3 magnitudes longer! $\endgroup$
    – PcMan
    May 19, 2021 at 16:26

2 Answers 2

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Submarines that support VLF communication (VeryLow Frequency) in the sub-30 kHz range can penetrate to 20m

Submarines that support ELF communication (Extremely Low Frequency) in the sub-300 Hz range can penetrate to 100s of meters.

If you species could generate (perhaps by touching the water with a special fin/organ) this type of frequency then communication would be possible to many interesting depths.

For more background on sub communications, this Wikipedia article is not a bad place to start: https://en.wikipedia.org/wiki/Communication_with_submarines

This was going to be my idea. And here it is, but deleted! I will addend in hopes of undelete by author.

The animals are dog sized. Their antennae are much larger.

https://www.livescience.com/3843-giant-balls-snot-explain-ocean-mystery.html

mucus web

Gastropods are mucus artisans. These creatures release enormous mucus antennae when they need to use VLF globespanning radio communications. Mucus would make a fine antenna - it can be imbued with electrolytes to facilitate transmission and it is recyclable, to be eaten and used again.

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  • $\begingroup$ Easy question: how long must the emitting antenna be at 30 kHz? $\endgroup$
    – AlexP
    May 19, 2021 at 16:01
  • $\begingroup$ I undeleted this at the request of @willk who has an interesting edit. $\endgroup$
    – JonSG
    May 19, 2021 at 16:29
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    $\begingroup$ I like this answer a lot. It's a good loophole that a) I had not considered, and b) could be evolved out of/tweaked to work on land, once they leave the ocean. $\endgroup$
    – AncientSwordRage
    May 19, 2021 at 16:52
  • $\begingroup$ @AlexP Not an easy question at all! Electrically short antennas are very common. In the linked Wikipedia article they mention antennas one 1000th of the wavelength long, but it's not obvious this is the minimum if there would be evolutionary pressure to shrink them. At the mentioned 30 kHz, that's about 10 meters. This might still be a bit too long, but it depends very much on how the radio signal is used. $\endgroup$
    – EdvinW
    Dec 8, 2022 at 18:07
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According to this paper

it has been shown in [4] that conventional RF propagation works poorly in seawater due to the losses caused by the high conductivity of seawater (typically, 4 S/m). However, fresh water has a typical conductivity of only 0.01 S/m, which is 400 times less than the typical conductivity of seawater. Therefore, EM wave propagation can be more efficient in fresh water than in seawater.

For such air-to-water communications, an optimum frequency range (3 - 100 MHz) was identified when the plane wave propagates to depths less than 5 m. In this optimum frequency range, the wave experiences significantly smaller losses than the losses at the lowest and highest frequencies of our analysis. Specifically, this frequency range includes the bands of short-wave radio (3 - 30 MHz), VHF TV (54 - 72 MHz, 76 - 88 MHz), parts of FM (88 - 108 MHz) and US military VHF-FM (30 - 88 MHz). Therefore, various communications systems can benefit from using the optimum operation frequencies that we identified here. Also, wireless power harvesting by wireless sensors can be significantly enhanced if it is performed inside the 3 - 100 MHz range.

Apparently within 5 m the communication at certain frequencies can happen. As a 0th order estimate, the 400 fold attenuation means this signal only travels 1.25 cm.

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    $\begingroup$ Good find, however two issues, one is that this is fresh water (I had assumed that this xeno-ocean is salt water, but I should clarify) and two, this is about the air-to-water surface boundary, not the deep ocean. $\endgroup$
    – AncientSwordRage
    May 19, 2021 at 11:59
  • $\begingroup$ I just noticed your change, does that mean that that the propagation in salt water is (5/400)m or 1.25 cm? $\endgroup$
    – AncientSwordRage
    May 19, 2021 at 15:40
  • $\begingroup$ @Pureferret, as a 0th order estimate $\endgroup$
    – L.Dutch ♦
    May 19, 2021 at 15:43
  • $\begingroup$ Can we take this up a notch based on this article? It appears optical transmission has proven successful (if not yet practical). Yes, the OP is asking for RF... but sometimes a frame challenge is in order. (Yes, biological creatures... but there are fish with lights in the depths...) $\endgroup$
    – JBH
    May 19, 2021 at 16:41

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