Where did you find this? I don't remember reading about it - could it be in his son's books?

Frank himself, you can get a clear picture of the ecosystem as outlined here by the end of Children of Dune.

One (possible) omission here - the sand trout traps water underground by linking and forming dams around water pockets - that’s the cause of Arrakis’ ultra arid environment, but maybe it’s also the source of nutrition?

Anyway, it is a bit silly indeed but in the novel’s context it feels grounded.

> Where did you find this?

I put together the pieces mentioned in various places in the first Dune book. Every step sounds good and plausibly science(-fiction)-esque when presented separately, like the book does. Only when you put all the steps together, the picture starts to look like an M.C. Escher drawing.

https://en.wikipedia.org/wiki/Waterfall_%28M._C._Escher%29

Pretty sure this is from either Children of Dune or God Emperor of Dune, both by Frank Herbert.