Animals that eat algae in the ocean include krill, shrimp, surgeonfish and turban and nerite snails. Additional creatures that eat algae include sea urchins, blennies and some species of crab.
Sheep crabs not only eat algae, but they sometimes place it on their carapaces for camouflage.
Krill are a type of decapod related to and resembling fish. Though they make up much of the diet of huge animals such as the blue whale and the whale shark, krill eat algae.
Surgeonfish are given their name because of the dangerously sharp spine near their tail. Still, they are sought after for aquaria. One species, the flagtail surgeonfish, is found in the coral reefs of the tropical seas. It scrapes algae from rocks and coral with its teeth.
Though there are many types of blenny, including freshwater, the lawnmower blenny is prized by aquarium owners for its ability to clean algae from tank glass. In the wild, it lives from the Red Sea to Micronesia around reefs with an abundance of algae.
Sea urchins are animals with hard shells covered with spines. There are hundreds of different kinds of sea urchins that live all over the world and can be found at any depth of the ocean. They are known to eat corralline algae in aquariums.