How West African manatees keep mangroves healthy

One Earth’s “Species of the Week” series highlights the flagship species of each of the 844 unique ecoregions contained within Earth’s bioregions.

Weaving in between the roots of partially sunken trees in the mangrove jungles of West Africa is a “forgotten” species. The West African manatee (Trichechus senegalensis), also known as the African manatee, is the least known and studied of the three manatees in its scientific genus.

Trichechidae is a family of sirenians, or sea cows, comprising all living manatees. The members include the Amazonian manatee, West Indian manatee, and West African manatee. However, the West African manatee is so elusive that biologists refer to them as the “forgotten sirenian.

African manatees live in coastal and isolated inland mangroves of such countries as Angola, Cameroon, the Democratic Republic of the Congo, Côte d'Ivoire, Equatorial Guinea, Gabon, Ghana, Liberia, Mali, Nigeria, Senegal, Sierra Leone, and Togo. They are found in waters above 18°C (64°F), including oceans, rivers, lakes, estuaries, lagoons, and bays. 

Sharing a common ancient ancestor with elephants, African manatees measure up to 4.5 meters (15 ft) in length and can weigh over 360 kilograms (790 pounds). They are gray with tiny, colorless hairs that cover their body. Yet, algae and other microorganisms often live and grow on African manatees, giving them a greenish hue.

Mainly herbivores, African manatees consume a variety of vegetation found above or hanging over the water. They eat about four to nine percent of their body weight in wet flora. Surprisingly though, the African manatee is the only sirenian who seems to intentionally diet on non-plant materials such as clams, mollusks, and fish.

Their diet of vegetation is what makes African manatees vital to their ecosystem. They prevent overgrowth and consume invasive plant species, improving the health of the mangroves. Manatee droppings also act as fertilizers for seagrasses and other aquatic plants.

This role is imperative to the well-being of the entire planet. Mangroves are a source of blue carbon or marine ecosystems that store ten times more CO₂ than tropical rainforests. These ecosystems also improve water quality by removing pollutants, protect soils and coasts from erosion, and provide a habitat for a vast amount of biodiversity.

Very social creatures, African manatees live in groups of up to six individuals. When they aren’t eating, they spend most of their time bonding by touch and verbal communication. As temperatures drop in the colder seasons, groups of manatees will join together to find food and warmer water.

Male African manatees are slightly smaller than females and take longer to mature -- about ten years. Female manatees can breed at the age of two to three, mating with multiple males year-round. One calf is born at a time after a 13-month gestation, and studies show there is a lifelong bond between a mother and her offspring.

In the Serer people of Senegal’s creation myth, the African manatee is viewed as the guardian of the secrets of the future. The Gambian and Mauritanian regard them as sacred and highly respected. Other West Africans have the legend of the Maame Water, the goddess of the sea and a symbol of wealth and beauty who flips over canoes and entices fishers to visit her kingdom.

Despite this notoriety, African manatees are considered vulnerable in conservation status due to illegal hunting for their meat and sometimes for their skin, bones, and oil used in traditional medicines and rituals. Deforestation of mangroves and wetlands from agricultural development and climate change also threaten the species.

The best ways to protect African manatees are through local awareness campaigns about the importance of the species and protecting their homes through ecosystem conservation. Efforts by the West African Manatee Conservation Project and Wetlands International are focusing on policy change and education to make sure this species is no longer forgotten.

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