The oceans are home to a wide variety of fish and mammals--from the tiny stout infantfish to the 100-foot-long blue whale. According to what they eat, sea creatures are classified into three groups: Carnivores, fish and mammals that eat meat; omnivores, fish and mammals that eat both meat and plants and herbivores, fish and mammals that eat only plants.
Green Sea Turtle
The green sea turtle has an incredible range of habitation, stretching from Finland to the tip of Cape Horn in Africa, though it generally prefers tropical and subtropical waters. The green sea turtle has a wide smooth shell, or carapace, and is named for the greenish colour of its skin rather than its shell, which normally is brown or olive in colour. Green sea turtles eat sea grasses and algae, though juveniles snack on crabs, sponges and jellyfish. In the wild, they can live up to 80 years and grow up to 5 feet long. They can weigh as much as 318kg. Unlike other sea turtles, the green sea turtle not only leaves the water occasionally to bask in the sun, but also, once mature, it is the only sea turtle that is strictly herbivore.
Manatees, sometimes called sea cows, move at a languid pace through coastal waters and rivers. Despite their bulk, they are graceful and powerful swimmers. Manatees use their tails to glide along at about 5 miles an hour, though they can manage 15 miles per hour for short distances. While they prefer to travel alone or in pairs, groups of about a half dozen are sometimes seen together. Their diet consists of water grasses, weeds and algae. Typically, manatees eat a 10th of their weight every 24 hours. Unlike seals or sea lions, manatees never leave the water. When resting, they can remain below the surface of the water for up to 15 minutes. While swimming, they surface to breathe every few minutes. The three different manatee species are distinguished by where they live. West Indian manatees primarily inhabit the southern waters of the United States but can range as far south as Guyana, South America. Amazonian manatees only live in the waters of the Amazon River. The West African manatees range along the western coastal waters of Africa from the Senegal River in Senegal to the Kwanza River in Angola.
Dugongs are related to manatees, which are both endangered and protected animals. These slow-moving herbivores graze on underwater grasses, rooting them out with bristled, sensitive snouts and chomping them with rough lips. Found in warm coastal waters, these enormous vegetarians are found from East Africa to Australia. Adults weigh between 500 and 0.454kg. They can grow up to 10 feet long with an average lifespan of 70 years. Like other sea mammals, dugongs can stay under water for short periods of time until they must resurface to breathe. The dugong can stay underwater for up to six minutes. Though they tend to be found alone or in pairs, when dugong herds gather, they can number in the hundreds.
Parrot fish are colourful and unique. They range in size from 1 to 4 feet. Of the 80 identified species, all can change their gender as well as their colouration and patterns. This ability makes it difficult for ocean biologists to classify the species. Parrot fish are algae eaters. They obtain the algae by ripping small chunks of coral from a reef. The coral is pulverised by grinding teeth found in the fish's throat. The teeth allow the fish to extract the algae from the centre of the polyp inside.
Many other herbivores thrive among the fish population. The surgeonfish family includes Achilles black-spot, blochii, blue hepatus tang, blue tang, brown, chocolate, convict tang, eyestripe, fowleri tang, Japan, lavender tang, powder blue tang, sailfin desjardinii tang, scopas tang and yellowtail tang. The blenny family includes bicolor, black, black sailfin canary, combtooth, flametail, lawnmower, lined, Midas, starry, striped and tailspot. The foxface family is comprised of the bicolor, foxface and magnificent. Unicornfish include the blond orangespine, orangespine and whitemargin. Other herbivores include the Japanese angelfish, yellow bloth rabbitfish and tilapia.