Apart this Horseshoe crabs are not crabs it’s a own species, nearest related to spiders and scorpions. They are raised since 1970 on sea farms as blood donors, which are taken a little out before freeing the animal again. Their blood (blue) is unique, because it contains a compound that detects the slightest bacterial contamination in medications and vaccines.
It’s important in medicine and Pharma industry, which also as collateral effect had avoided the extiction of this animal, which before was in a real risk.