 Crabs are typically scavengers, meaning that they eat whatever they can find, and as omnivores this includes both plants and other animals.In a study conducted on seaweed crabs living on the coast of the South Island of New Zealand, the foreguts were opened among a sample of crabs to determine what foods had been consumed.Algae, including calcareous red algae and branched brown algae, was identified as the most commonly eaten substance, as it was found in nearly all of the crabs sampled.