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Harnessing the Superpowers of Seagrass - Project Manaia in the Med

Updated: Aug 22, 2022

Via their Ocean Gardeners programme, Project Manaia is building a seagrass restoration network in the Mediterranean Sea

Since January 2022, Deutsche Stiftung Meeresschutz (DSM) has been supporting Project Manaia, founded by Austrian marine biologist Manuel Marinelli. The focus is on establishing a network of diving bases, dive centers and marine field stations across the Mediterranean to preserve and replant local seagrass meadows.

The project is also designed for citizen scientists. Vacationers and locals can drop off intact torn seagrass plants and seagrass seeds at Ocean Gardener Stations. The network stations store the dropped-off plantlets and seeds for later insertion into existing meadows. In order to accomplish this, each station of the network receives a "renaturation kit" consisting of: Information flyers for guests and participants, aquarium with compressor and bubbling stones for longer storage of seagrasses and seagrass seeds, containers for collecting seagrasses and seagrass seeds as well as material needed for planting. Costs for these are covered by DSM, Greenpeace Foundation and Project Manaia.

But why seagrass, one might ask? This feature explains the critical role which this miracle plant plays in the life of the oceans and the planet.

Seagrass Meadow, Ischia. Photo by Project Manaia

Seagrass - wonder weapon against the climate crisis

Nature-based solutions (NbS), such as conservation and renaturation of potent CO2 storage systems like seagrass beds, are nowadays among the most promising and cost-effective approaches in the fight against climate change and global mass extinction. The CO2 storage potential of seagrass meadows is often underestimated and insufficiently researched.

  • Just recently, researchers from Max Planck Institute for Marine Microbiology (MPIMM) in Bremen published a study showing that seagrass stores excess CO2 in the form of sugar in the surrounding seafloor.

  • The concentration of sugar (sucrose) in the seagrass rootstocks studied off Elba, in the Caribbean and the Baltic Sea was at least 80 times higher than anything previously measured in the ocean.

  • An additional advantage is that the sea grasses protect their sugar reserves from degradation by microbes, by releasing phenols into the sediment which keep the microorganizms out. The researchers estimate that around 600,000 to 1.3 million tons of sugar are stored in the root zone of seagrass meadows worldwide - as much as in 32 billion cans of coke, according to MPIMM.

  • Depending on their location and species, seagrasses store at least 30 to 50 times more CO2 per unit area than forests on land. What's more, they do it much faster, about 35 times faster.

  • One square meter of replanted seagrass sounds like a little, but that area – a mere one square meter - stores up to 83 kg of carbon.

  • Seagrass meadows worldwide are currently thought to store up to 15 percent of the climate gas CO2 absorbed by the ocean (at least 25 million metric tons). It is also advantageous that their storage activity is largely underground. Yet they cover only about 0.2 percent of the ocean floor. This CO2, which is removed from the atmosphere for a long time, is known as "blue carbon".

Seagrass Meadow by OceanImageBank, Umeed Mistry.

Hotspots of biodiversity, and more

It is also often overlooked that the seagrass meadows are hotspots of biodiversity. Experts estimate that around 40,000 fish and around 50 million invertebrates (like lobsters, octopods, shrimp) live and feed on 4,000 square meters of seagrass meadow. Species such as the endangered green sea turtle depend almost entirely on seagrass food for survival.

At the same time, seagrass secures the substrate it grows on.

Seagrass Meadow by OceanImageBank, Stefan Andrews.

Large Crab in Seagrass Meadow, by OceanImageBank, Michiel Vos

Catshark in Seagrass Meadow. Photo by OceanImageBank Shannon Moran

The sorry state of the Mediterranean Sea

The Ocean Gardeners project focuses on the Mediterranean Sea which is under extreme pressure. It is one of the most overfished, most frequented by ship traffic and most littered seas. In addition, it suffers from mass-tourism by many millions of tourists every year and from numerous bio-invasive foreign species. Warming of ocean temperature and acidification of seawater are particularly high in the Mediterranean Sea, putting additional strain on the marine ecosystem.

Solution: Neptune grass (Posidonia oceanica)

Neptune grass is a species of seagrass endemic to the Mediterranean Sea. It is often referred to as the Lungs of the Mediterranean. It grows very slowly, about 1.5 to 2 cm a year, grows to 1.5 m tall, has blades about 1 cm wide, lives for many hundreds of years, and forms meter-high rhizomes packed with stored carbon dioxide.

Neptune grass is also a special marine plant for another reason. It can fix nitrogen with the help of a symbiotic relationship with nitrogen-fixing bacteria, much like legumes on land do (beans or peas). Research shows that there is a small set of specialist microbes which overcome the phenols and do digest the sucrose. It is speculated that these may live in a beneficial relationship with the seagrass by providing nutrients it needs to grow, such as nitrogen. This is extremely rare in the ocean.

Mapping sea grass meadows

Over the past four years, Project Manaia has been conducting large-scale mapping of Neptune grass meadows in the Mediterranean. In this way, it is known whether a meadow is growing or shrinking over the years.

All of the meadows studied are shrinking.

This poses a serious threat to the countless species of marine life that depend on this ecosystem for survival. It is also causing the Mediterranean Sea to increasingly lose its ability to store CO2.

This is where Project Manaia and their Ocean Gardeners programme step in, establishing seagrass meadows, restoring what has been lost, and creating the opportunity for others to be involved in the process. They have already established several Ocean Gardener Stations and are working at expanding the network significantly.

Ocean gardener measuring a seagrass meadow in the Mediterranean Sea. (Photo by Project Manaia)

Specific aims of the Ocean Gardeners project

The Ocean Gardeners network is intended to span the entire Mediterranean Sea. The aim is to increase the CO2 storage capacity of the Mediterranean Sea as a whole and reduce the CO2 content of the air masses above the surface of the sea and in the seawater itself. Such local effects can also have a positive dampening effect on seawater acidification. In addition, the project will strengthen biodiversity in the Mediterranean and rebuild it where it has declined.

By engaging divers, dive centers and the general public in reporting sightings of seagrass, collecting seagrass seeds, planting recovered seeds and replanting recovered seagrass, over time these aims can be achieved, with a significant impact on the problems associated with climate change and the biodiversity crisis to avoid mass extinction.

Interested? Join in, while on vacation at the Mediterranean Sea, or as a diving base or diving center. Become part of the Ocean Gardener network! Please contact:

Project Manaia, Manuel Marinelli:

Feature submitted to Scubavox by DSM, July 2022

Seeds can be easily stored in a jam jar filled with salt water. Best in the refrigerator, where the seeds will keep for weeks and months. (Photos by Project Manaia)

Dropping anchor in sea grass is not a good idea. Often grasses are torn off during retrieval. (Photo by OceanImageBank, Dimitris Poursanidis)

Project Manaia Research Sailing ship, SY Independence

Seagrass Meadow, Ischia. (Photo by Project Manaia)

1 Comment

Aug 09, 2022

Awesome work - had no idea seagrass did so much, will definitely look at those little blades differently now!

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