A sea thermometer – saving Posidonia for ocean preservation

Ocean preservation and climate action in the Mediterranean Sea – exploring Posidonia meadows’ effect on marine biodiversity, the global climate, and marine ecosystem’s health

Ocean preservation: What does Posidonia do for us and the oceans?

Posidonia is a seagrass that forms vast and dense meadows along the Mediterranean basin’s coast. As with all seagrasses, the ecosystems created by the Posidonia are rich in species; they are like underwater forests similar to rainforests located but in marine environments instead.

These species living in these Mediterranean meadows are part of a community of organisms that specialized to live within the canopy of Posidonia. In terms of ocean preservation, the value of this seagrass goes beyond the biodiversity it supports with the ecosystem services it provides. 

Protecting Posidonia – one of the climate action solutions along coastal areas

Among them are its role as a nursery for fish species, the provision of oxygen, its action as a carbon skin, sequestering carbon from the atmosphere, which contributes to reducing the CO2 in the atmosphere, and protecting the coastline. That’s why protecting Posidonia is one of the climate action solutions we can enact along coastal areas. 

«Posidonia is a slow-growing plant. In a way, it’s like a tree that lives in the marine environment». Explains Gabriele Procaccini, Director of Research at the Anton Dohrn Zoological Station. «The Posidonia mat is much like a coral reef protecting the coastline from the wave action and the wave energy. When it is forced to disappear, the coastline is subjected much more than before to erosion and the removal of sand caused by the wave action». 

What are the threats to Posidonia? Climate change and its effects 

Posidonia meadows are undergoing not only geographic distribution but also a decrease in shoot density. One of the leading causes for this phenomenon is the impact of the global changes we observe in our marine environments: temperature increases and water desalination. 

«Another way global climate change can be detrimental to these ecosystems is through ocean acidification caused by increased CO2 levels. For now, it is well demonstrated that Posidonia meadows are not suffering much at the present levels of CO2 in these waters. Still, we don’t know what will happen when the acidification of the oceans increases. In Ischia at the Aragonese Castle, a natural laboratory is studying the effects future ocean acidification levels can have on organisms thanks to the natural CO2 vents that can be found in the area because of the region’s volcanic activity».

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Human action vs. ocean preservation: how human behaviors are impacting Posidonia

While climate change is staining Posidonia, local threats also impact this seagrass. These threats affecting Posidonia in loco are caused by human action. Some alter the environment in which the Posidonia lives, like the changes in the local hydrodynamic regime caused by the construction, for example, of barriers or marinas on the coastline. Anchorage, on the other hand, can lead to the plant’s direct removal. 

The main culprits behind this issue are recreational boats, which tend to crowd the Mediterranean Posidonia-rich coastlines, for example, touristic areas and towns like the Italian island of Ischia and Capri, in particular during summers, the local high season.

Protecting Posidonia and Science News: understanding ecosystems

«We are conducting studies to understand what temperature threshold Posidonia can’t survive. Our findings are quite optimistic. We are seeing that Posidonia is much stronger than we previously thought, as it can survive notable temperature increases. But of course, there is a limit. We are seeing that when the Posidonia is subjected to high temperatures, it starts to ‘breathe’ at higher rates, using the reserves it has accumulated during the growing season, summer. So in the long term, temperature increases will surely be detrimental for Posidonia». Said the Director of Research at the Anton Dohrn Zoological Station. 

That, though, isn’t the sole issue that comes with higher temperatures, as these bring new marine species. With the increase in temperatures, these new tropical species that were until recently unknown to Posidonia environments are now invading, entering the Mediterranean, and changing the ecosystem’s equilibrium. 

Enacting effectual ocean preservation and Climate action solutions

«It is not easy in such a short time to determine which species is more dangerous for Posidonia because that is something that ecosystems will take longer to show us. But of course, the equilibrium that the ecosystem has reached during evolutionary times will be changed by the increase of alien species». 

The Suez Canal, which connects the Mediterranean and the Red Sea, was officially opened on 17 November 1869. In the 150-odd years since the canal was opened, many species have entered the Mediterranean from the Red Sea, with several of them being tropical species, now expanding northward due to the temperature increase. Among these invading species, there are also other seagrasses like the Halophila stipulacea. This small tropical seagrass species is native to the Red Sea, Persian Gulf, and the Indian Ocean, from which it reached the Mediterranean, and can now be found in its southern and eastern parts.  

Climate action solutions – ocean preservation and climate action meet when we protect Posidonia

The Posidonia meadows are considered highly valuable at a European level thanks to their ecological credentials. Their presence is one of the parameters considered when designing the boundaries of marine protected areas.

«When it comes to mitigating the threats Posidonia is facing, protection and management are the two keywords. What we can do to protect the meadows on a local level is protect them from anchorage, from changes in the coastal hydrodynamic regime, and the apportion of sediment. While all of this can be done at the local level, on a global level, what we can do is climate action aimed at trying to stop the global climate change that is and will strongly affect our life now and in the near future». Said Gabriele Procaccini

Carbon burial – biomass under Posidonia meadows, removes carbon from the atmosphere

Given the value of reducing the emissions of Carbon Dioxide (CO2) emissions for ocean preservation and preserving the plant’s livability, local action aimed at protecting the Posidonia meadows scattered across the Mediterranean coasts makes for a highly beneficial climate action solution. 

The mat, the dense biomass located under Posidonia meadows, removes carbon from the atmosphere through carbon burial. Since the mat soaks up carbon, when Posidonia is subjected to direct removal through the anchorage of boats, that leads to the remission of the previously buried carbon into the mat. That’s why protecting the Posidonia meadows from direct local threats can mitigate global climate change and its effects. 

Posidonia restoration – science for climate action solutions 

The members of the scientific community working with Mediterranean seagrasses have been dedicating time and work to perfecting the Posidonia restoration process. Currently, several companies are trying to find the most effective way to restore and transplant this seagrass. That task, though, is as complex as it is expensive. In addition to that, the results so far have been rather inclusive. If we consider projects with longer monitoring times, there have been a few successful restoration projects, but we don’t know how the situation could evolve in the long run.

In terms of perfecting Posidonia restoration, the scientific community is experimenting with the possibility of transplanting seeds and seedlings instead of adult plants. If this endeavour were successful, we could avoid collecting plants from one meadow to a new one. This would be a step forward for Posidonia restoration as collecting the plants from preexisting meadows impacts doner meadows.

Perfecting Posidonia restoration – experimenting with transplanting seeds and seedlings

«There are still many things to be done to make this successful. With my research group, we are working on the aspects related to the genetics of transplanted plants, trying to determine how valuable genetic polymorphism is for transplants and how the genetic similarity between donor and acceptor sites influences the success of transplantation. We are also working on reinforcing transplants and material by applying techniques that make individuals more resistant and more capable of growing when they are transplanted».

Anton Dohrn Zoological Station

Anton Dohrn Zoological Station is a research institute located in Naples, Italy. It was founded in March 1872.

Roberta Fabbrocino