[Wonder Warthog]

"I don’t believe that mollusks exist for us to eat, because their diet is scavangers."

Mollusks are filter feeders that eat phytoplankton and zooplankton, not waste.

[Jonty30]

Mollusks keep water in a nitrogen balance.
https://www.whoi.edu/oceanus/feature/can-clams-and-oysters-help-clean-up-waterways/