The answer is d. predation.
Hunting in packs, Orcas will attack and stun a seal by throwing it up into the air. It is assumed that hunt and prey upon crabeater seals like they do most other seals, although there has not been documentation of such behaviors with Crabeater seals.
Fun facts: Crabeater seals eat krill instead of fish, and over 80% of crabeater pups are prey for the more vicious, carnivorous leopard seals! :D
