Not much is known of the roles of southern elephant seals while they are at sea. However, they are known to be important to their ecosystem as predators of fish, sharks, squid, crabs, and shrimp and as prey for large sharks, killer whales, and leopard seals. Another important role they play in the ecosystem is as a host for many kinds of parasites. Some of the known parasites include tapeworms, acanthocephalans, and the louse Lepidophthirus macrorhini.
- the louse Lepidophthirus macrorhini