Sirenian

The sirenians are the only entirely aquatic, herbivorous marine mammals, making them unusual among mammals and marine mammals. Their whole life cycle, like that of the cetaceans, takes place in the water. They may have been mistaken for mermaids by early explorers. As sirenians only eat water plants, they tend to congregate around beaches where humans can be found in large numbers. When it comes to the Sirenia species, Sirenia is a minor order with only two extant families, Dugongidae and Trichechide, each with four species. There is only one living member of the Dugongidae family of dugongs. West Indian manatees (Trichechus manatus), African manatees (Trichechus senegalensis), and Amazonian manatees are all members of the Trichechide family (Trichechus inunguis).

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Here, we will learn about different types of Sirenia species, Sirenia animals, lifespan, habitat, and diet of sirenians.

Pezosiren Portelli

Pezosiren Portelli is a 50 million-year-old basal sirenian from Jamaica's early Eocene. A Jamaican fossil skeleton serves as the type specimen, which was reported in 2001 by Daryl Domning, a marine mammal paleontologist at Howard University in Washington, DC. It is said to live an amphibious existence similar to that of a hippopotamus, and it is a superb example of a transitional form between a land mammal and a sea mammal. The fossil closely resembles the Prorastomid family's oldest known member.

P. Portelli had the same basic head and body shape like most modern sirenians, such as manatees and dugongs, but he also had four limbs that had not yet been changed into flippers, with well-developed feet and hands that were still adapted for land walking.

Prorastomids evolved into dugongs (there were formerly many dugong species in the Caribbean, but currently there is only one species found in the Pacific and Indian Oceans) and manatees after they arrived in the Caribbean and Americas millions of years ago (which are believed to have originated in an ancient inland sea in South America that today is the Amazon basin).

As a result, the manatees we see today in Africa are not direct descendants of their ancient ancestors, the Prorastomids, who lived there. Instead, the manatee family (Trichechidae) formed in South America and later crossed the Atlantic Ocean, most likely a few hundred thousand years ago, though the precise time range is unknown. So, today's African manatees have returned to the continent where their forefathers initially originated 50 million years ago. 

Lifespan

The typical longevity of a sirenian is 50 to 70 years, with a maximum lifespan of roughly 73 years. Predation, habitat disturbance, hunting, poisoning from various contaminants, and disease are among factors that contribute to adult mortality, especially in cooler waters. Due to overcrowding caused by habitat degradation, sickness has recently become a severe problem. To maintain their population size, sirenians are thought to need a survival rate of 90 percent or greater. Manatees survive significantly better in captivity than dugongs, which are frequently taken at young ages and must travel larger distances.

Habitat

Sirenians can be found in a wide range of tropical and subtropical aquatic environments. All of them enjoy the water that is at least two meters deep and has a lot of submerged aquatic vegetation. Sirenians prefer coastal, marine areas, but Amazonian manatees prefer freshwater environments in the Amazon Basin. During the colder months, sirenians in subtropical areas prefer warm, freshwater, and are frequently spotted in the warm water near coastal power stations. During the summer, they migrate to tepid saline waters. Sirenians can't survive at water temperatures below a specific point. If the water temperature drops below 20°C (68°F), West Indian manatees migrate, African manatees prefer temperatures above 18°C (64°F), Amazonian manatees prefer higher temperatures, around 25° to 30°C (77° to 86°F), and dugongs tolerate no temperatures below 19°C (66°F). It is potentially lethal if temperatures fall below certain levels. In fact, exposure to cold waters is one of the leading causes of death among sirenians.

Feeding Ecology and Diet

Manatees consume a wide range of vegetation, including submerged, floating, emergent, shoreline, and overhanging plants. The dugong's diet consists mostly of marine grasses. Both manatees and dugongs have been observed eating benthic invertebrates, and some manatees have even been observed eating fish. The Amazonian manatee is largely a surface feeder, while the West Indian and West African manatees feed on the bottom to the surface and above. The dugong, on the other hand, is a bottom feeder. Manatees move plants with their flippers and mouth vibrissae. Similarly, dugongs eat every portion of the plants they eat, uprooting them in the process. Cornified plates on the anterior regions of the upper and lower jaws of both manatees and dugongs break vegetation and move it back for additional crushing by the molars. Because dugong tusks only sprout in adult males, it's unknown what role they play in eating. Manatees and dugongs have a single stomach compartment with an associated digestive gland, which is followed by a similarly substantial enlargement of the upper small intestine with its associated duodenal ampullae. The caecum connects the small and large intestines, which can reach lengths of 65.6 ft (20 m) each. The sirenians, like the horse, are hind-gut digesters who break down cellulose into volatile fatty acids that may be absorbed by the gut using a variety of anaerobic microbes in the large intestine. The passage of food takes roughly a week. The sea cow has no teeth and used the cornified plates on its upper and lower jaws to crush ingested kelp. It appeared to eat mainly the surface of the water and algae growing on exposed rocks at low tide. In aquaria, manatees consume roughly 10% of their body weight in plants (wet weight) per day. Both manatees and dugongs spend a significant amount of time feeding in the wild.

Sirenians mainly plant such as seagrasses, water weeds, and other aquatic vegetation so they are known as herbivorous sirenians. 

West Indian Manatee

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All sea cows, including the West Indian manatee, are herbivorous. This manatee's brain is small in comparison to its body size, as it is in most herbivores, owing to the fact that it does not need to develop intricate hunting methods to catch prey. It pulls seagrass from the soft sediments it grows in with its thick, extremely movable lips.

West Indian manatees like warm water and migrate between warm, winter locations and fruitful, summer places on a yearly basis. Some warm springs, tropical coastal seas, and artificially warm locations generated by coastal power stations serve as wintering grounds.

The Florida manatee (Trichechus manatus latirostris) and the Antillean manatee (Trichechus manatus latirostris) are the two recognised subspecies of West Indian manatees (Trichechus manatus manatus). Manatees of the other two species can be found in Brazil and Africa.

Throughout much of its range, the West Indian manatee enjoys some or complete legal protection, although it is nevertheless targeted in some areas and is threatened by habitat degradation, boat collisions, and accidental capture in fisheries targeting other species. As they are prevalent in recreational boating locations and are sluggish, poor swimmers, boat crashes are probably the most serious hazard to this species. Scientists believe the West Indian manatee is vulnerable to extinction because populations are low in some areas and regionally extinct in others. It may be lost from more sites if human activities that harm this species are not carefully managed.

West African Manatee

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Of the three manatee species in the genus Trichechus, the African manatee is the least well-known. The African manatee is supposed to resemble the more well-known American manatee in look and behaviour.

Habitat and Ecology of  West African manatee

The West African manatee can be found in a variety of habitats, including maritime coastal areas, lagoons, estuaries, and river tributaries, where it lives in salt, brackish, and freshwater. They like mangrove areas and calm water and are only found in water that is 18°C or warmer. During the night, they eat and move around. Aquatic vegetation from overhanging bank growth, mangroves, and submerged aquatic plants make up the majority of their food. The West African Manatee is said to eat fish from nets and rice from fields in some areas, putting them at odds with the surrounding human population. The West African manatee is mainly found in solitary or small family groups in island locations, but groups of up to 15 individuals have been seen. Adult females give birth to live young that can grow up to 1m in length. Breeding is supposed to take place all year.

Amazonian Manatee

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The Amazonian Manatee (Trichechus inunguis) is a manatee species that dwells in the Amazon River and its tributaries' freshwater environments. The Amazonian manatee is the only manatee that can only be found in freshwater. The species is placid and slow-moving, and it may often be spotted eating on the surface of the lakes and rivers it calls home. As a result, it is relatively easy to hunt, and its oil, meat, and skin are threatened as a result of past and ongoing hunting for these purposes. Pollution, unintentional drowning in commercial fishing nets, and vegetation deterioration due to soil erosion caused by deforestation all pose threats to manatees.

Habitat and Ecology of Amazonian Manatee

The Amazonian manatee lives entirely in the water and never leaves it. It is a herbivorous species that feeds on grasses, water lettuce, and water hyacinths, among other aquatic and semi-aquatic plants. It consumes a lot of plants, about 8-15 percent of its body weight on a daily basis. Manatees must spend a lot of time eating because much of this food is of low quality. They feed at the surface and are assumed to be active at all hours of the day and night.

Sirenia Sea Cow

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The dugong is a sea cow that can be found in the Indian and western Pacific Oceans at warm latitudes. It is the only living member of the Dugongidae family, and its closest living relatives are manatees.

It grazes largely on seagrasses and thus spends the majority of its time in seagrass beds. The dugong, unlike its close relatives the manatees, never enters freshwater and is hence the sole herbivorous marine animal. The brain of the dugong, like that of most herbivores, is small in comparison to its physical size, owing to the fact that it does not need to develop intricate hunting methods to catch prey.

Internal fertilization allows dugongs to procreate and give birth to enormous young, which they nurse for up to a year and a half. Adult dugongs have no natural predators, but juvenile dugongs are vulnerable to saltwater crocodiles, killer whales, and large coastal sharks.

The dugong is protected throughout much of its range, yet it is nevertheless hunted in some regions and is threatened by habitat loss, boat crashes, and unintentional capture in fisheries aimed at other species. Scientists believe the dugong is vulnerable to extinction because populations are low in some areas and regionally extinct in others. The dugong could become extinct in additional places if human activities that threaten it are not carefully managed.

Fun Facts About West Indian Manatees

• Manatees from the West Indies can weigh up to 1,200 pounds (544 kg) and grow to be around 10 feet (3 meters) long.

• Every day, West Indian manatees consume 15% of their total weight in seagrass and vegetation. It's possible to consume up to 150 pounds of food per day.

• In the winter, West Indian manatees travel to warmer waters since temperatures below 68 degrees Fahrenheit can be fatal.

• Manatees from the West Indies may venture into freshwater rivers and springs.

• West Indian manatees sleep for 10 to 12 hours each day.

• Manatees in the West Indies can hold their breath for up to 20 minutes underwater, but they normally surface every few minutes to breathe.

• Manatees in the West Indies swim at a speed of 3 to 5 miles per hour (4.8-8 km per hour)