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.