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Posidonia oceanica meadows

Since 1997 the Posidonia meadow in Mataró has been the subject of a scientific monitoring project with volunteers from the Societat de Pesca i Activitats Subaquàtiques de Mataró (SPAS), coordinated by the Escola del Mar de Badalona and the support of Mataró Town Council. The aim of this project is twofold: on the one hand, to know the current state of this habitat and, on the other, to transmit its value as a natural heritage to society. Each year the project publishes the data in an annual report.

Posidonia oceanica is a seagrass species that is endemic to the Mediterranean Sea. It forms large underwater meadows, also called prairies. Mataró has one of the most important meadows in terms of extension. Posidinia oceanica is not an algae, but a terrestrial plant that adapted to living under the sea milions of years ago. It grows at depths from 0 to 40 meters, where the light enables the photosynthesis process.

Posidonia oceanica is a marine phanerogam, a superior plant with corm structure, with histological and reproductive specialization: it has roots or rhizomes, stem, leaves, flowers and fruits with seeds, thus differentiating itself from algae.

There are only about 60 marine phanerogams species distributed throghout the seas and oceans of the planet, thus presenting a low diversification. There are five existing species specifically in the Mediterranean Sea, being Posidionia oceanica the most emblematic and important species of the Mediterranean, since it is an endemism of this sea— that is to say, it can not be found anywhere else in the planet.

The meadows on the coast of Mataró cover around 700 ha and can be found at a few meters depth, but the distance can also be higher than 27 meters in some points.

21 fish species can be found in the grassland of the coast of Mataró. 13 out of these 21 fish species are considered resident populations in this ecosystem, while 8 are considered random species.

The importance of the conservation of Posidonia meadows as an ecosystem lies in the great biodiversity it hosts.

It is the habitat of many organisms. Many species lay their eggs on it protecting them from predators and juvenile fish find in it a shelter until they reach adulthood.

Posidonia acts as a biological filter by storing carbon and thus reduces the CO2 present in the atmosphere, thus reducing the effects of climate change.

In addition, it immobilizes metals, hydrocarbons and other toxic substances in roots and rhizomes, retaining them and leaving them out of circulation from the food web.

Species to be highlighted: the comber (Serranus cabrilla), the painted comber (Serranus scriba), the common two-banded sea bream (Diplodus vulgaris), the annular bream (Diplodus annularis), the Mediterranean rainbow wrasse (Coris Julis), the ocellated wrasse (Symphodus ocellatus), the axilliary wrasse (Symphodus mediterraneus), the damselfish (Chromis chromis) or the grey wrasse (Symphodus cinereus).

Meadows are among the most productive ecosystems of the planet. In addition, some of these species are of commercial interest.

Without Posidonia oceanica, the sea would be a place with less fishing, fewer beaches, dirtier waters, but above all there would be less life.

Posidonia oceanica has roots or rhizomes, stem, leaves, flowers and fruits with seeds, thus differentiating itself from algae.

Knowing about Posidonia and its function will help us respect it.

Posidònia 2021

POSIDONIA 2021 is an environmental initiative born from the concern of different people and groups of Mataró and the Maresme with the aim of promoting the conservation and recovery of its Posidonia grass meadows and the many species that are part of the same ecosystem.

The declaration of the Generalitat de Catalunya of this area as a Special Conservation Zone (ZEC) within the Xarxa Natura2000 from 2014 provides clear proof of the fragility of these sea beds and especially of the Posidonia oceanica. Therefore, it recommends that aspects such as preventive management, environmental improvement, sustainable use and ecosystem restoration should be effectively and feasibly implemented throughout the protected area.

From the beginning, this project had a great support both at institutional and private level, which enabled the signing of the first Agreement of Marine Custody in Catalonia with the participation of Associació Posidonia 2021, Ajuntament de Mataró and Generalitat de Catalunya.

Posidonia 2021 has recovered the boat named Vell Marí, located at Dock K2, used to disseminate the undertaken actions to schools.