From Portbou to Alcanar: this is the Catalan seabed

BarcelonaThere are up to 26 different marine habitats along the Catalan coast. However, until now, some were unknown, or, despite their existence, the exact location and size of their habitats had not been identified. To fill this historical information gap, a pioneering project was launched four years ago to produce a detailed x-ray of the Catalan seabed, which was presented this Thursday: the map of marine habitats of Catalonia. "For the first time, we have information on the entire Catalan coast, from Portbou to Alcanar," explained Sara Pont, head of the heritage planning service at the Department of Environmental Policies and Natural Environment.

The project, which has cost 4 million euros –75% financed through the European Maritime and Fisheries Fund–, has made it possible to determine that the Catalan seabed is mainly made up (93% of the coast) of three large environments of mud and sandy mud, mud and sand with numerous shells and remains of the organisms that live in the area). Now, the digitalized map –which can now be consulted here– It also identifies points on the Catalan coast where there are underwater tunnels and caves, such as off Begur, or large meadows of posidonia, such as on the Maresme coast, at Cap de Creus, and a few kilometers inland from the beaches of Vilanova and la Geltrú.

In total, the survey has covered the entire Catalan coast, X-raying up to 50 meters deep with meter-by-meter details of nearly 190,000 hectares. To achieve this, various technologies have been combined: an airplane with bathymetric LIDAR to determine sea depth, ships with echo sounders and sonars, and remotely guided underwater vehicles.

Beyond the more interesting points, the broad distribution of these marine habitats is as follows: between the northern Costa Brava and the Maresme, sand and muddy sand predominate, and in the southern part, between northern Barcelona and the Ebro Delta, there are muddy and sandy mud bottoms. The variation in these habitats depends largely on sedimentary processes due to the presence of large rivers such as the Ebro, the Llobregat, and the Besòs, and the effect they cause when they reach the sea.

Furthermore, in some areas of the Costa Brava, and especially in the Maresme, biogenic detrital bottoms predominate, with a mixture of gravel, boulders, sand, and remains of echinoderms such as starfish, sea cucumbers, and urchins. This type of seabed allows for the creation of ecological niches that ultimately become refuge and feeding areas for a wide variety of flora and fauna species.

Areas of interest

At the presentation of the map, the Regional Minister for Territory, Housing and Ecological Transition, Silvia Paneque, said that this new tool will allow "planning and carrying out sustainable management of the uses and activities that take place in the maritime environment" and that the project has made it possible to "obtain better information on the location of the areas of greatest natural value and that must be conserved, since they have very important functions ... community interest, which correspond to submerged and semi-submerged underwater caves, estuaries and deltaic mouths, rocky seabeds and meadows of oceanic posidonia. The latter are considered the most important ecosystems in the Mediterranean, both for their size and, above all, because they are a crucial habitat that provides refuge for many marine species, and their slow growth gives rise to very stable and long-lived seagrass beds. Along the Catalan coast, there are up to 4,582 hectares of posidonia meadows, representing 2.4% of the mapped area.

In addition to the materials that make up the seabed, the map also includes the elevation model of this seabed and the bathymetry (the relief of the seabed), which allows us to understand the geomorphology of the seabed, as well as the depth.

Sunken ships?

As explained by the Director General of Environmental Policies and the Natural Environment, Marc Vilahur, the inspection of the seabed also revealed various elements "that have been identified in great detail." These elements range from infrastructure belonging to the Catalan Water Agency (ACA) to "many pieces of debris, such as cars carried by the river" and archaeological remains.

In the latter case, Vilahur explained that they are "elements of different types and different periods," which could include a sunken ship. However, the Director General stated that this information is still being analyzed further and will be kept solely within the Cartographic Institute and will not be made public or appear on the map to protect the heritage.