Crabs are caught and killed in massive numbers with methods that may cause significant suffering given emerging evidence of crustacean sentience.
Crabs boiled alive or frozen slowly likely experience distress if they have any capacity for suffering. Their nociceptive responses and behavioral changes following tissue damage meet many criteria for morally relevant pain experience. More humane killing methods like mechanical spiking exist but are rarely used commercially. Capture and confinement before death also involves stress.