What is the vulture of the sea?

shark?

Perhaps the Great White (Carcharodon). You didn't say how many letters. There are sharks that are harmless, so if the word is longer, or has different letters, then you have to find the name or genus of that shark. There are many different species. Those that are most known to eat anything and everything are the Great White, oceanic whitetip, tiger, and bull sharks.

http://www.trueauthority.com/cvse/sharksprnt.htm

http://en.wikipedia.org/wiki/Great_white_shark

Depends on what the dead thing is and how big it is. If we're talking floating corpses then sharks are your answer, though I suspect killer whales are adaptable enough to do this as well.

If we're talking something lying dead on the bottom and slowely rotting then you've got just about every detritus eater available; sea cucumbers, borrowing or free-roaming worms, flatworms, sea stars, brittle stars, snails, anything that lives on the bottom.