The nets capture everything in their path and damage the meadows, in figures they can reach up to 1000 kg of leaves (dry weight) per hour. It also causes turbidity, anoxia (oxygen deficit) and excess of nutrients. It is illegal in depths inferior to 50 meters.
With permanent structures or with anchors and chains, which tear the posidonia away from its substrate and release paint and antioxidants that are toxic.
Sport and fishing ports, breakwaters, artificial beaches and other buildings on the coastline. They destroy the meadows, modify the hydrodynamism, potentially intensifying water flows, and the sediments trigger the burial of the plant and turbidity, which hinders the arrival of light, preventing the posidonia from carrying out photosynthesis and dying.
Large extensions of vegetation are eliminated to allow the growth of mollusks.
The extraction of sediments directly causes the complete loss of the seagrasses and, indirectly, mobilization of remains, turbidity and excess nutrients.
Plastics and toxic products commonly used, such as sunscreen.
Pollution by spills
The compounds of which accumulate in the tissues of posidonia and are toxic, produce turbidity that obstructs the passage of light and progressively bury the plant.
Of the ships, like fuels and oils.
Industrial, such as coal, petrochemicals, detergents, fertilizers, herbicides, pesticides, paper, heavy metals, salt, etc.
The desalination plants spill harmful products and brine, increasing the salt concentration in areas with the presence of posidonia, exceeding its tolerance threshold.
In summer, the population increases due to massive tourism, which is why the sewage treatment plants saturate themselves above their capacities and release the water without being sufficiently purified.
It is an excess of organic matter and nutrients (essentially nitrogen and phosphorus) coming from wastewater, rain, rivers, aquaculture, air pollution and agricultural fertilizers.
This excess causes the proliferation of phytoplankton and algae that reduce the level of light that can reach the plant, limiting photosynthesis and growth.
The microbial activity increases, which causes the sediment anoxification (decrease in available oxygen).
It increases the amount of herbivores that feed on posidonia leaves, such as the sea urchin or the salema porgy, decreasing the photosynthetic surface.
The organic and inorganic particles increase the turbidity, preventing the passage of light.
Large concentrations of reduced compounds of nitrogen (ammonium) and sulfur (hydrogen sulfide) are toxic to plants and inhibit photosynthesis.
Posidonia stores the surplus of nitrogen, reducing the carbon reserves that will be necessary in times of less luminosity.
Global warming and heat waves increase the temperature of the air and the sea, which decreases the amount of available oxygen, decreases the growth of the leaves and rhizomes and when it exceeds 28°C triggers the death of posidonia.
The rise in sea level causes the displacement of the seagrasses towards the coastline.
The amount and intensity of storms increase.
It can increase the salinity and the turbidity of the waters.
It is a chain effect, since posidonia is key to absorb carbon dioxide and climate change reduces its extension, decreasing the amount of posidonia to sequester CO₂ and accentuating climate change even more.
Invasive exotic species
Like other marine plants that compete for resources and can modify habitat characteristics. This causes the destruction or displacement of seagrasses.
They develop well when temperatures rise. Compete for resources and place above the posidonia, preventing the light from reaching it and carrying out photosynthesis, causing its death, as well as producing harmful substances that kill the living beings that inhabit the posidonia.
Because of all this, in a few years posidonia has seen its extension reduced:
In Spain 29%
In Formentera from 30% to 40%
In France 9%
In Italy 25%
In Albania 16%
In Tunisia 2%