Located in front of the Ría de Vigo (Pontevedra, Galicia, Spain) is the ZEC/ZEPA Illas Cíes, within the Atlantic biogeographic region, with a very small stable human population, in its scope the Cíes Archipelago is included, made up of the islands of Monteagudo or Norte, Faro or del Medio and San Martiño or Sur, as well as the islets of A Agoeira or Boeiro, Penela dos Viños, Carabelos and Ruzo; being the most abrupt islands of the Galician Atlantic coast, their highest point is Alto das Cíes, with a height of 197 meters.
The Cíes Archipelago is home to natural values of great interest from the point of view of conservation. A large part of these environmental assets are submerged under water, although the areas of high ecological value are not limited only to marine waters, their depths and the fauna that inhabits them, but on the emerged surface there is a high biodiversity, both in habitats and species, with endemic and scarce elements in the continental territory. In addition to having unique geological formations. Among the most important ecosystems for conservation present in the Cíes Archipelago, we can mention the seabed, the dune ecosystems, the coastal scrublands and the coastal lagoon “Lago dos Nenos”.
The biocenotic diversity of the seabed of the Cíes Islands archipelago is based on a coastal configuration that, by presenting different orientations in the face of marine hydrodynamics and oceanic influence, and the presence of a variety of habitats settled on the rocky and sandy coast: cliffs, rock of little inclination, caves, beaches etc., allows in turn a high specific richness of these bottoms. Therefore, depending on the area in question, the environmental conditions and the biodiversity of the environment clearly vary, distinguishing up to three clearly differentiated areas (Conaima, 2006). In the areas most exposed to hydrodynamics, "forests" of large brown algae (pheophytes) and horizons of red algae (rhodophytes) can be found, depending on the area in question. In addition, the exposed and semi-exposed walls are home to barnacles, mussels and barnacles. Likewise, populations of white corals and gorgonians (Eunicella spp.) (Conaima, 2006) stand out in more protected semi-exposed areas. Maërl beds are present in the southeastern area of the archipelago. The two most representative coralline algae that form maërl are Lithothamnion corallioides and Phymatolithon calcareum, both of which are included in Annex V of the Habitat Directive. In the Cíes archipelago, the maërl beds present a high diversity, with 95 species (Peña & Bárbara, 2006).
In the emerged surfaces of the Cíes archipelago, more than 20 ha correspond to dune systems, among which those of Rodas and Muxieiro-Figueiras stand out. In these systems, various active, hygrophilic and non-remounting dune belts can be found, characteristic of the embryonic dune, the white dune and the gray dune. Integrated into the gray dune are also hygrophilic dune environments or moist intradune depressions. Also noteworthy is the presence of active dune systems occupying clearly raised topographic surfaces with respect to the high tide level, under the denomination of remounting dunes.
Linked to the dune system of Rhodes is the Lago dos Nenos coastal lagoon, a shallow, saltwater lagoon that forms part of a lagoon-barrier system, next to the sand barrier that extends from Punta Muxieiro to Cabo Punta das Vellas. , with an approximate length of 1 km, including Rodas beach. One of the peculiarities of this system is the permanent contact with oceanic waters through its western margin and sporadically with the Ría de Vigo through a punctual constitution channel in times of spring or temporary tides.
As for the flora and fauna of the Cíes Archipelago, it has a significant number of species of interest for conservation, with a total of more than 90 species with some category of European, state or regional protection, mostly corresponding to birds, being a place that houses various colonies of migratory birds.
Among the flora, the presence of Erodium maritimum stands out, a species with few known populations in Spanish territory, which is found in the surroundings of the Cíes lighthouse (Gómez Orellana & Sáez Gonyalons, 2004). The mid-dune species Linaria arenaria is also of great interest (Blanco-Dios, 2008). Populations of Rumex rupestris have recently been recorded in the Cíes Archipelago (Carbajal et al., 2005). On the other hand, the maërl-forming coralline algae, Lithothamnium corallioides and Phymatholithon calcareum, should not be overlooked.
With regard to invertebrates, the Cíes Archipelago has populations of two lepidoptera with protection categories, Zerynthia rumina, considered the smallest papilionid of all those known in the world and classified as Endangered by the Galician Catalog of Endangered Species, and Euphydryas aurinia, included in Annex II of the Habitat Directive. As for marine invertebrates, it is possible to find the sea urchin Echinus esculentus (Castiñeira, 2005) and the white gorgonian Eunicella verrucosa in the waters of the archipelago.
The ichthyofauna of interest for conservation is characterized by five species included in Annex II of the Habitat Directive, which may be present in the waters surrounding the Cíes Archipelago. These are Alosa alosa, Alosa fallax, Petromyzon marinus, Chondrostoma arcasii and C. duriense.
On the other hand, the importance of the Cíes Archipelago for birds lies mainly in the wintering population of the Yellow-legged Gull (Larus cachinnans), which has come to exceed 20,000 specimens, accounting for 95% of the total population counted in winter in the Spanish state, being considered one of the largest European colonies of this species. Also highlighting the populations of European Shag (Phalacrocorax aristotelis) and Turnstone (Arenaria interpres) (Martí & Del Moral, 2002). The populations of the European storm-petrel (Hydrobates pelagicus) and the black-backed gull (Larus fuscus) are also considered to be of great importance in the Cantabrian-Atlantic Spanish context (Domínguez et al., 2003). In addition, the common guillemot (Uria aalge) is also present, although only as a winterer, documenting its disappearance as a breeder in 1988 (Arcos et al., 1995).
Finally, among the mammals it is possible to highlight those present in the marine environment of the Cíes Archipelago, which is frequently visited by various cetaceans, among which the species Phocoena phocoena, Tursiops truncatus and Delphinus delphis stand out.
The high conservation values of this archipelago make it a remarkable space at the Spanish level, presenting a high interest for the interpretation of natural heritage by society. This has led to its inclusion, among other figures, in the Parque Nacional Marítimo-Terrestre das Illas Atlánticas de Galicia (Law 15/2002), which receives around 450,000 visitors throughout the year, with the Cíes archipelago receiving approximately 70% of the visits. The declaration of the National Park makes it possible to regulate visits in an orderly and sustainable manner (which are carried out by disembarking at the points set up for this purpose), through the corresponding Governing Plan for Use and Management (PRUG) approved by Decree 177/ 2018, avoiding significant effects on the state of conservation of natural components.