Seabirds provide fertilizer for sea grass , which cleans the water and provides homes for many fish and food for herbivorous fish and shrimp,and even manatees and green sea turtles .
Sharks keep down populations of octopuses,when sharks are removed octopus populations explode and ruin crab and lobster populations.
Certain sharks such as hammerheads keep down populations of rays and skates, where these sharks are missing or infrequent the ray population can get overbalanced and destroy commercially important mollusk such as clams,oysters,mussels,abalone,scallops and prawns