Ok. So. Some of you may recall me picking your collective brain for help with something or other for the sci-fi series I'm writing. I'm looking for ideas again. There is a mostly ocean world, the only land masses of which are hundreds, perhaps thousands, of small islands. There are two castes of the same amphibious race, one which lives on the surface, and one which lives in underwater caves. They are in a symbiotic relationship, but are having a dispute. I want thoughts about how they are symbiotes, and what the dispute is about. Something involving natural resources? Something on the surface islands the cavers need, and something in the underwater caves the islanders need? I'm leaning toward the cavers feeling unappreciated or taken advantage of in some way, and withholding their end.