Five years after Gloria, its footprint remains visible in many parts of the Mediterranean coast. However, the underwater consequences are less known. This meteorological episode devastated seabeds, which may take more than a century to recover. Research teams from CEAB-CSIC have studied its impacts on ecosystems, both on land and in the sea. One of these studies has focused on Posidonia oceanica.
Researchers from the Centre for Advanced Studies of Blanes (CEAB-CSIC) observed the loss of large extensions of Posidonia meadows on the seabed during their first dives shortly after the storm. Due to the massive waves, many meadows experienced the worst regression ever recorded since monitoring began. Later, this scientific team continued studying Gloria’s impacts on Posidonia. They conducted surveys in 42 meadows across different parts of the western Mediterranean, particularly along the Catalan, Valencian, and Murcian coasts, as well as in the Balearic Islands. The dives allowed them to assess the extent and type of impacts (burial, unearthing, and uprooting) suffered by the meadows.
The results of this research were recently published in 2024 in a scientific article: Evaluating the extent and impact of the extreme Storm Gloria on Posidonia oceanica seagrass Meadows, in the journal Science of The Total Environment.
One of the main conclusions is that the predominant impact of Storm Gloria was the unearthing of plant shoots, leaving them exposed. Over half of the sites analyzed showed recent signs of unearthing, with sediment losses of up to 40 centimeters.
Although less frequent, burial also had a significant impact. In some locations, it was critical, with plants buried under more than 7 centimeters of sand, leaving only their uppermost parts visible. This leads to the death of Posidonia, as it cannot survive with more than 6 centimeters of sand covering it.
Furthermore, recent signs of plant mortality were observed in the meadows, along with large amounts of debris floating on the seabed or accumulated on beaches. Posidonia losses extended to meadows at depths greater than 20 meters, the limit of their distribution due to their dependence on light.
Another key conclusion is that fragmented and more exposed meadows were far more vulnerable to the storm’s impacts than those that were continuous, in better initial condition, and more protected by their natural surroundings.
Candela Marco-Méndez, a researcher at CEAB-CSIC and author of the article, explains: “Storm Gloria is a clear example of how global change intensifies extreme weather events, endangering vital ecosystems such as Posidonia meadows.”
Teresa Alcoverro, also a researcher at CEAB-CSIC and co-author of the scientific article, adds: “It could take over a hundred years for the meadows to recover. They regenerate slowly, but we often don’t allow them to. As a society, we still don’t fully grasp the importance of conserving these and other natural ecosystems. Marine meadows provide us with numerous benefits: they are vital for water quality, act as refuges for many species, store carbon, and protect the coast from disturbances.”
As part of ongoing research (Marco-Méndez et al.), it has been shown that Posidonia meadows impacted by Gloria, such as those in Mataró or Cala Canyelles (Lloret de Mar), may experience long-term mortality after extreme events. This is due to the unearthing and uprooting of shoots, a subject this research seeks to study in depth. The same study analyzes how these lasting negative effects lead to the loss of ecosystem services (e.g., carbon storage in meadow soils). It has also confirmed, once again, that human impacts such as pollution and coastal urbanization significantly reduce the resilience of marine meadows, making them much more vulnerable not only to extreme storms but also to less intense phenomena like regular winter storms or even daily wave activity.
The researchers emphasize the need for managers to use existing scientific knowledge and continuously generated insights to promote effective marine meadow protection measures. They stress the urgency of acting to conserve these vital ecosystems, not only for their environmental importance but also for the essential services they provide, such as carbon capture and coastal protection.
Ref.:
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Marco-Méndez, C., Marbà, N., Amores, Á., & Alcoverro, T. (2024). Evaluating the extent and impact of the extreme Storm Gloria on Posidonia oceanica seagrass meadows. Science of the Total Environment, 908
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Marco-Méndez, JF Pagès, X Seglar, G Muñoz-Ramos. Efectes dels temporals extrems als herbeis de Posidonia oceanica i a la consciència mediambiental col· lectiva Atzavara, L’ 33, 87-98
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Gera, A., et al. (2014). The effect of a large storm event on the seagrass Posidonia oceanica. Marine Pollution Bulletin, 83(2), 565–573.
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Cabaço, S., et al. (2008). The impact of sediment burial and erosion on seagrasses: A review. Estuarine, Coastal and Shelf Science, 79(3), 354–366.
L'entrada Lasting consequences of storm Gloria ha aparegut primer a CEAB.