Jack told me a theory on Cig a long time ago. He said the dinoflagellate Gambierdiscus, that produces the toxin, is very similar to the lichens that are the first to populate a new lava flow (not sure how long that takes) And this was why Cig was rather rampant in the S Pacific after WW2. The US and Japan both dynamited reef structure to get material to build airfields and roads on the islands. The dinoflagellate quickly grew on the newly exposed calcium cabonata.
If that's true, it makes sense that parts of the Big Isle with new lava flows interring the water may have higher levels of Cig?
I've never heard that theory actually, but it sounds interesting. From my experience, I've observed the opposite. the most cig prone areas are generally on the west side, the side with older lava flows,more coral cover, dry climate and warmer water. The east and south east side especially has relatively new lava, less coral cover and more rain, and generally less reported cases of cig. May be due to the smaller population compared to kona. I've come to understand that G. toxicus likes to grow on macro algae (seaweed/limu).
What makes sense is areas of disturbance like bombing having high incidence of cig. Coral death and bleaching will expose the CaCo skeleton of coral ( not basalt/lava), a good place for turf algae to grow, providing a good environment for gambierdiscus to settle.
There is definitely much more that we can learn about ciguatera, I'll look into the lichen theory.