Most of us may unknowingly refer to them as “nuisance algae,” but algae meadows are a true gift from nature. In addition to their rich ecosystem services, scientists have in recent years studied their importance in storing carbon dioxide and what happens to it when pastures are degraded or destroyed.

Such studies are currently being carried out in Rhodes by the Hellenic Center for Marine Research (ELKETHE) with the participation of scientists from three countries: the team is led by Eugenia Apostolaki (ELKETHE researcher) and her colleague Oscar Serrano from the National Research Center. Council of Spain (CSIC) and Briac Monnier and Vassilis Dacos of the French National Center for Scientific Research (CNRS). The research for the South Aegean dressage program is co-funded by the NSRF (Coordinator George Hatiris, ELKETHE Researcher).

Algae grasslands are responsible for over 10% of the carbon stored in the oceans each year, even though they occupy only 0.2% of the world’s oceans. In the Mediterranean, Posidonia grasslands store carbon at depths of up to 11 meters, making it the largest carbon store of any grassland in the world.

“Sea grasslands are one of the largest carbon stores in nature,” explains Ms. Apostolaki. “This happens in two ways. On the one hand, algae photosynthesize, like all plants, and thus produce organic carbon. At the same time, they act as ‘traps’, retaining organic carbon that is in the water. This gradually leads to the creation of biogenic reefs composed of dead tissue and sediment.These reefs act as carbon stores, as the lack of oxygen decomposes the carbon within them very slowly.The reefs are especially impressive in the case of the Posidonia oceanica species (see famous Posidonia grasslands), which form reefs up to 11 meters high and 9,000 years old, being one of the largest natural sinks of carbon on the planet.”

The scientific team is investigating the vulnerability of these reservoirs of “blue carbon” (as the carbon sequestered in the sea is called) by studying the case of Posidonia Meadow in Pefko Bay in Rhodes. The choice is not accidental: the coastal regions of Rhodes are under repeated pressure from the development of tourism, and at the same time they are among the areas of the country with the strongest increase in sea temperature.

An ELKETHE study in Pefki Bay on Rhodes has shown that over the past 500 years, 7939 tons of organic carbon remained at a depth of one meter!

The meadow was mapped by the ELKETHE team and found to cover 45% of the bottom surface at a depth of 5 to 30 meters with a total area of ​​about one square. kilometer. “We measured the concentration of carbon per square meter of sediment. Using carbon-14 radiodating, we calculated that 7,939 tons of organic carbon have been preserved inside the meadow at a depth of one meter over the past 500 years,” explains Ms. Apostolaki. “However, pastures are showing signs of degradation, and we estimate that about 12% of pasture cover has been lost over the past 30 years.” As part of the project, the ELKETHE team conducted on-site experiments to measure the potential increase in greenhouse gas (CO2, CH4) emissions and estimate the carbon loss due to pasture loss. It is expected that the results of the project will contribute to an increase in knowledge about the spatial and temporal variations in blue carbon accumulation, especially in light of global environmental changes. “The value of sustainable management of coastal blue carbon ecosystems and ensuring their integrity has been recognized as a natural solution for climate change mitigation, adaptation and ultimately coastal resilience,” notes Mr. Apostolakis. “However, anthropogenic disturbance and climate change are causing widespread degradation of these ecosystems, perhaps reducing their ability to store carbon, but also causing stored carbon to be released back into the atmosphere, turning these ecosystems from carbon sinks to CO2 sources.” For this reason, including grasslands in national climate change strategies can help Greece meet European climate targets.”

The importance of Posidonia pastures is not limited to blue carbon storage. “Poseidonia provide rich ecosystem services,” explains Vassilis Gerakaris, PhD in marine ecology at the Elkete Institute of Oceanography. “They are a habitat and breeding ground for many marine organisms, a refuge in the first stages of their life, a food field for many species. At the same time, they help improve water quality by binding and recycling nutrients, removing pathogens, and producing oxygen. At the same time, they help to reduce coastal erosion, acting as a natural breakwater.”

ELKETHE has recently begun mapping the Posidonia meadows in Greek waters, estimating an area of ​​2,600 sq. km.

Community legislation characterizes the grasslands of Posidonia as “priority habitats”. In Greece, their protection is heterogeneous and is usually limited to a few marine protected areas (Natura 2000), although both the European Commission and the Council of State have frequently pointed out the need to protect everything.

“In general, the state of the marine meadows in Greece is very good, unlike the countries of the Western Mediterranean. We do not have phenomena of mass degradation,” says Mr. Gerakaris. “However, there are also problems in our country, near urban centers, in closed bays and in tourist areas. The main problem is the uncontrolled anchoring of boats, especially in the Cyclades and the Ionian Sea. That is why the correct mapping of Posidonia is very important, so that either boats are prohibited in these places, or moorings friendly to sea meadows are set up.