One thing I kept thinking about when reading this was whether these crabs ate their moult. When a crustacean moults, it is unarmored and vulnerable. In fact, many crabs don’t even bother feeding or coming out from a good hiding spot for a month while they wait for their new exoskeleton to harden (helped along by the recycled Calcium). The benefit is lost if crabs eat their moult. This is a common practice in insects as the moulted exoskeleton may provide a first post-moult meal before retreating to safety to harden the carapace. Some hermit crabs, including the coconut crab, are known to eat their moults. It would be interesting to see a comparative study of several different types of crab from polluted vs. clean sites that are known to eat or not eat their moults. Also, perhaps doing a similar study on crabs that are known to ingest moults and have a treatment allowing them eat and treatment removing moults (not allowing them to eat) to see if metals are being reingested from the moult.