The Paralithodes camtschatica is surrounded by an environment full of organisms. Because the individual crab is so different in each stage of development, the relationships to other species differ to each stage. Also to keep in mind is the different environments the crab lives in during several periods in its life and the types of organisms that live there as well.
The larvae crab lives in shallow water, swimming around among the plankton. The zoea larvae use the plankton as their food source as well as protection, the plankton keeping the zoea away from predators such as the filter feeding organisms. Organisms that filter feed the seawater tend to stay away from the plankton infested areas, thus not taking in the zoea in the plankton.1 Although predators of plankton, the zoea are also prey to the many other animals living around them, including aquatic worms, sea urchins, and barnacles. Aquatic worms, such as the Carcinonemetridae family, have been found to also feed on many decapod eggs, thus given the name, the Nemertean Egg Predators. They are capable of doing so because of the crab's external fertilization.2
When the red king crab begins its megalops stage, it migrates to the ocean floor. These juvenile crabs are still susceptible for much predation, thus hiding under rocks, in crevices and trenches, and using the kelp to keep hidden from predators.3 They have a predatory relationship with the kelp, the crab not only receives protection, but also the kelp is part of the juvenile king crab’s diet. The small crabs start becoming predators like the adult forms, feeding on kelp, sea stars, clams, muscles, barnacles, etcetera. The megalops crabs are still under much predation, being easy prey for many fish, example being cod, as well as other crab species and invertebrates.4
The adult red king crab is also a well known predator of the echinoderms, sponges, worms, mollusks, and small fish. Because of the red king crab’s defensive carapace and claws and large size, they have fewer predators then megalops. Predators of the king crab include the octopus, seal, and humans.5 The Alsakan king crabs also come into contact with a special type of barnacle, the Briarosaccus callosus, which acts as a parasite, causing “sterilization and reduced growth” to the king crab.6 Also, the adult king crab uses kelp and other substrates as protection during mating and molting, when their hard carapace is gone.7