Many species with long and narrow leaves and often spread across large meadows resembling grassland; many species superficially resemble terrestrial grasses.
Seagrasses most occur in shallow and sheltered coastal waters anchored in sand or mud bottoms. Most species undergo submarine pollination and complete their life cycle underwater.
Seagrasses beds/meadows can be either made up of a single species or in mixed beds.
Seagrass beds are diverse and productive ecosystems, and can harbour hundreds of associated species for example juvenile and adult fish. Few species were originally considered to feed directly on seagrass leaves partly because of their low nutritional content , but scientific reviews and improved working methods have shown that seagrass herbivory is an important link in the food chain, feeding hundreds of species, including green turtles, dugongs, manatees, fish, geese, swans, sea urchins and crabs. Some fish species that visit/feed on seagrasses raise their young in adjacent mangroves or coral reefs.
Seagrasses trap sediment and slow down water movement, causing suspended sediment to settle out. Trapping sediment benefits coral by reducing sediment loads, improving photosynthesis for both coral and seagrass.
The United Nations Environment Programme has warned that fishing trawlers, seaweed farming, and tourism on the coasts of Tanzania and Kenya are threatening the survival of seagrasses.
The UN body wants countries to include seagrass protection and restoration in their nationally determined contributions to help reduce the amount of heat-trapping carbon in the atmosphere.
In its new report titled ‘Out of the blue’: The value of seagrasses to the environment and to people, launched on World Oceans Day on June 8, UNEP blames these unsustainable activities for a deteriorating coastal ecosystem, a decline in coastal productivity, and affected certain supportive functions performed by the marine plant leading up to loss of critical fisheries habitat.
Known as the “lungs of the sea” due to their role in producing oxygen in the water, the flowering plants that grow entirely underwater perform numerous functions, including stabilising the sea bottom, providing food and habitat for other marine life, and provide numerous other services to coastal communities. East Africa’s coast has 12 known seagrass species.
Seagrass ecosystems are biologically rich and highly productive, providing valuable nursery habitats to more than 20 per cent of the world’s largest 25 fisheries and filtering pathogens, bacteria, and pollution out of seawater.
The Out of the Blue report showcases the many ways that seagrasses help people thrive and sustain the healthy natural environment that we all depend on.
Seagrasses can help us solve our biggest environmental challenges. They purify water, they protect us from storms, they provide food to hundreds of millions of people, they support rich biodiversity, and they efficiently store carbon.
UNEP said new data suggest that seagrasses are among the least protected coastal habitats. In a recent census it was estimated that seven per cent of seagrass habitat is being lost worldwide each year.That is close to a football field of seagrass lost every 30 minutes.
The survey also found at least 72 seagrass species in decline around the world. Since the late 19th century, almost 30 per cent of known seagrass area across the globe has been lost. The main threats to seagrass meadows include urban, industrial, and agricultural run-off, coastal development, dredging, unregulated fishing and boating activities, and climate change.
Yet, seagrass beds in the region, according to the UNEP support sizeable populations of two endangered species, the greenturtle, the marine mammal (dugongdugon) and seahorses, both of which feed on seagrasses.
They act as nursery, breeding and feeding grounds for marine fish and crustacean species of economic importance such as shrimps and spiny lobster.
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