Why does there appear to be no evidence of remains at the seven site? An obvious answer could be the fragility of the carapace but I don’t know, never been close enough to a Coconut crab.
Historically, westerners who are not familiar with Birgus latro are more concerned about him eating them than vice versa. The
Norwich City survivors were astounded when the rescuing native boatmen were delighted to find Coconut crabs on the island.
What about the Hermit Crabs? At least they would leave a shell behind and we know from the clam bushes that these are able to survive.
Hermit crab shells are, of course, borrowed and are, by definition, recyclable. The shell used by any Strawberry Hermits eaten by the castaway would likely be reclaimed by another Strawberry Hermit.
BTW, although the Gilbertese do reportedly eat them, I would have no idea how to go about eating a Strawberry Hermit crab. They're about the size of a jumbo shrimp but they have a much thicker shell.