What are the primary producers of Arrakis?

Question

Here on Earth, we have a number of primary producers:

• Plants and other photosynthetic organisms, which convert sunlight into chemical energy.
• Chemotrophs, which get energy (via a few intermediate steps) from geothermal activity.

What are the primary producers of Arrakis? The planet receives a lot of sunlight, and is geologically active, but I do not know of any organisms in the Dune canon that use either of these energy sources.

Answer 1

You give the answer yourself:

The Ecology of Dune mentions that they [the sandworms] eat sand plankton, which themselves feed on traces of spice melange, but this seems circular.

It is circular in respect to matter, but that's how all ecosystems work: plants are eaten by herbivores, which are eaten by carnivores, which (after they die) are eaten by bacteria, which produce fertile soil, on which plants grow.

What an ecosystem also needs is a constant supply of energy, which is what distinguishes primary producers: they are the organisms through which energy enters the food chain.

On Earth, one of the most important primary producers is phytoplankton. Thus, to me the name "sand plankton" implies that it plays the same role, presumably using sunlight as its energy source, via photosynthesis or a similar process.