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Beaches in Barcelona’s metropolitan area unexpectedly act as butterfly reserves

Vegetació dunar a la platja de Castelldefels en ple esclat primaveral. Autor: Robert Ramos (AMB)
Vegetació dunar a la platja de Castelldefels en ple esclat primaveral. Autor: Robert Ramos (AMB)

The third report of the mBMS, Barcelona’s Metropolitan Butterfly Monitoring Scheme, contains some unexpected findings: the beaches in Barcelona’s metropolitan area are not only inhabited by butterflies, but by butterfly communities unlike those found in the local parks. This means that the beaches act as reserves for certain species of butterflies. Some species found in only relatively small numbers in parks are more abundant at beaches, making such seaside environments especially important for biodiversity conservation in the metropolitan area.

“We know very little about beach-dwelling butterfly communities, so the mBMS data are particularly interesting,” says Joan Pino, director of the Centre for Ecological Research and Forestry Applications (CREAF), professor of ecology at the Autonomous University of Barcelona and scientific coordinator of the mBMS. “Environmental conditions at the beaches are very extreme, so only very specific plants grow there, and only certain species of butterflies can live among those plants,” he continues. “The fact that some species are much more abundant at the beaches than in the parks means that the beaches are vital to metropolitan butterfly conservation, so it is essential to ensure that their vegetation is well managed.”

The report also sets out the general results of the mBMS in 2021. Overall, in the parks and beaches studied, the 50 volunteers participating in the project spotted 2,205 butterflies of 40 different species (20% of all the species present in Catalonia).

This year’s season “has got off to a slow start, because of lower temperatures than usual in early spring,” explains Joan Marull, director of both the mBMS and the Ecology and Territory Department of the Barcelona Institute of Regional and Metropolitan Studies (IERMB). “But with the recent rainfall and the warm temperatures on the way, May will be a great month for butterflies, so we will be able to make a good start to the fourth mBMS campaign,” he adds.

The mBMS will include five new parks in 2022, taking the total number of parks and beaches it covers to 26. The mBMS is run by the Barcelona Metropolitan Area administrative body (AMB), in cooperation with the IERMB and CREAF, through a body that the three organizations established in 2018, the Metropolitan Laboratory of Ecology and Territory of Barcelona (LET).

Butterfly reserves

In all, 17 species of butterflies have been identified at the beaches studied. The most abundant of them is the common blue (Polyommatus icarus, also present in large numbers in parks), followed by two species more dominant at the beaches than in the parks: the painted lady (Vanessa cardui) and the clouded yellow (Colias crocea). “In the metropolitan area’s parks, 10 species of butterflies account for almost 75% of all sightings, but at the beaches, because of the more extreme environmental conditions, the dominance of a handful of species is even greater, with almost 85% of sightings corresponding to just five species,” remarks Joan Pino. Volunteers record sightings of butterflies at four beaches in Barcelona’s metropolitan area, namely Castelldefels Beach (where the number of individual specimens spotted is highest), Gavà Beach, La Murtra Beach (Viladecans) and El Remolar Beach (El Prat de Llobregat).

In the 17 metropolitan parks studied in previous years, the three most common species of butterflies are the small white (Pieris rapae), the common blue and the geranium bronze (Cacyreus marshalli), which is an invasive species relatively new to the area. The three parks with the most diverse butterfly communities are Els Pinetons Park (Ripollet), El Canal de la Infanta Park (Cornellà de Llobregat) and El Calamot Park (Gavà).

Five new parks

The five new parks included in the mBMS in 2022 are La Costeta Park (Begues), L’Ermita del Pla de Sant Joan Park (La Palma de Cervelló), Can Lluc Park (Santa Coloma de Cervelló), Can Rigal Park (Barcelona) and La Bastida Park (Santa Coloma de Gramenet). The project thus covers a total of 26 parks and beaches distributed among 13 municipalities in the metropolitan area. To continue furthering knowledge of butterflies, which are regularly used as bioindicators, the mBMS is looking to recruit volunteers willing to undergo training and commit to monitoring butterflies in a park or at a beach of their choosing. Anyone wishing to volunteer should fill in the registration form available on the project’s website (http://mbms.creaf.cat/).

Support for dune vegetation and wildflower meadows

The project’s results underline how important seaside dune and beach vegetation is to butterfly conservation in Barcelona’s metropolitan area. Its findings, “like many other data, make it clear that these singular plant communities are among the area’s biodiversity hotspots and that we need to continue looking after and improving them, as the AMB has been doing for years,” states Jordi Bordanove, coordinator of the AMB’s Services for the Promotion and Conservation of Public Spaces.

As far as the metropolitan area’s parks are concerned, the results of the mBMS are unequivocal: wildflower meadows that are rarely mown, never watered, and untreated with herbicides or plant-protection products have more diverse butterfly communities than traditional grass fields or watered lawns. With that in mind, the AMB has a policy of nurturing wildflower meadows wherever doing so is compatible with the public’s use of parks. “We encourage wildflower meadows, as far as possible, as we are very aware of their benefits in terms of biodiversity and related ecosystem services,” says Bordanove. “Furthermore, they help to significantly improve the landscape and make parks more resilient to adverse environmental events, such as infestations and droughts,” he concludes.

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