On the coasts of the world, from the tropics to the Arctic Circle, thousands and thousands of bright green stems swing from an underwater meadow in shallow waters: seaweed meadows. The jungle of leaves and root balls is a unique ecosystem in which microscopic algae floats like great manatees. The lemon-yellow seahorses cling to their gripping tails and the crabs suck out fleas, along with small snails that nurture the growth of algae. The little starfish walks slowly on small suction feet, surrounded by tiny transparent prawns.
In the rug of thick leaves of seagrass meadows, many marine creatures find shelter, benches, hiding places and food. Underwater lawns are also the architects of their environment: they trap sediments, reduce flow velocity, slow erosion and produce oxygen. Without seaweed, the coasts below and above the water would look vastly different. The seagrass ecosystems of the Mediterranean and all of their inhabitants are now particularly vulnerable.
The endangered Poseidon meadow
Seaweed rarely blooms, and often does not reproduce through sexual contact. They reproduce most often by horizontal root shoots, that is, genetically identical clones. These stocks grow slowly, but they can become very large and very old – in the Mediterranean they can sometimes reach an area of more than 15 km and Reach 80,000 years! Underwater meadow grass is not vegetarian at all: the sixteen species of seaweed with several species belong to the Alismatal family. Each plant grows from two to six leaves, narrow and long toward the sunlight at the surface of the sea. At the bottom, they anchor themselves firmly in sandy ground with roots and branching roots and turn these roots into adhesive discs on rocky surfaces.
- Thanks to their close-knit roots, they stabilize the loose sea floor and act as breakwaters to protect coastlines from erosion.
- They take in a lot of carbon monoxide2 It releases oxygen,
- They provide shelter for many species such as a nursery for fish and other marine animals, including important food resources for humans,
- They filter sediment particles and other suspended matter from the water, improving water quality, and
- They hunt microplastics and sometimes even roll it onto the ground.
Because seaweed grows slowly, it cannot adapt quickly to new environmental conditions. Additionally, there is low genetic variability of clonal societies, as the plant reacts like any other to disturbances such as fluctuations in temperature or salinity. The cloning community finds it difficult to cope with the warming of the ocean and its consequences: in the western Mediterranean, they spread after two waves of heat and as a result of the warming In general it slowed down significantly Especially the seaweed that is only found in the Mediterranean Poseidonia It reacts with a special sensitivity.
There, on the coasts that are heavily used by tourists, seagrass meadows are also threatened by mechanical damage Due to illegal mooring. Slow-growing frog plants cannot compensate for the damage caused. At the same time, they face increasingly strong competition from large invasive algae migrating from the Red Sea through the Suez Canal – growing faster and better tolerating heat.
The seaweed filters the plastic from the ocean and rolls it back onto the land
The gradual disappearance of seaweed is likely to have consequences. Maybe also the ones that you might not think of at first. One example is plastic pollution, which is a major problem on the Spanish Mediterranean coast and around the Balearic Islands. In the Spanish region of Almeria, it has been on the rise since the 1970s, when the industrial cultivation of fruits and vegetables began under plastic sheeting: UV rays and the wind break down films of a large area, tearing them apart and blasting them across the landscape. The plastic pieces break down into smaller and smaller pieces and finally end up in the sea with wind, rain or waterways; Including many particles smaller than five millimeters in size: microplastics.
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