Most recently saw this mentioned in a post about a diving helmet here https://www.seaofthieves.com/forum/topic/75921/diving-helmet-new-item/9
Giant Clams need to be sprinkled around most every island as another form of random loot.
- All underwater.
- Some deeper than others.
- Some buried in the sand only visible by bubbles.
- Others on the floor and visible from a distance.
- Special animated interaction to dig them up, open them.
- Some snap shut on an arm or a leg and require a button mash sequence to break free.
- Some are empty, others have pearls of various worth.
- Every once in a while you'll find a Pearl of the Merfolk. Possibly magic of some kind. Could be a special undersea voyage. Or just worth lots if given to a mermaid.
Basically a simple reason to explore the cool underwater features.