Animals that die become food for animals that are still alive. That's how the whole system works and it keeps the fixed amounts of essential ingredients on the move. YOU contain carbon atoms that were part of any king or tsar you care to mention - you have over a million atoms in you that were part of Socrates, Genghis Khan, Joan of Arc or any historical figure that interests you. The detritus that falls to the sea bed is food for all the little worms and greebies that live down there. They in turn become food for the fish - which you may eat one day and complete the cycle. Fun!!!