crabs, mollusks are regarded historically by native peoples as food only when hunting is very bad and starvation is a possibility.
Mussels are a prime source of B12 and manganese (stress, bones and metabolism). Crab is wayyy higher in b12, but it’s heavy in selenium and copper, both toxic in large amounts (neurologic/psychologic). In a starvation situation, I’d definitely be hunting mussels over crab, well, if I knew then what I know now. Maybe they knew, too?