The Atlantic Islands of Galicia Marine-Terrestrial National Park is made up of the Cíes, Ons, Sálvora and Cortegada archipelagos and the surrounding marine waters. These islands, which have very steep and rugged coastlines (with many cliffs and sandy deposits), are part of a mountain range that sunk into the sea many millions of years ago, where schist, granite and gneiss predominate.
The Cíes Islands are an archipelago made up of three islands: Faro Island (106.6 ha) and Monteagudo Island (179.5 ha) are joined together by an old dike, while San Martiño Island (145.5 ha) is the one furthest south; they also include the islets of Penela dos Viños, Ruzo, Grabelos and Agoeiro. They protect the Ría de Vigo against the inclemencies of the weather (strong winds and heavy rain) coming in from the ocean. The island of Monteagudo is separated from Cape Home by a strait called Verga de Sotavento, and connected to the island of Faro by an old dike and by Rodas Beach (from 1,300 m), which in turn is separated from the island of San Martiño by a 500-metre wide strait known as Freu da Porta.
The Cíes Islands are mountainous (the highest peak is Alto das Cíes, standing at 197 m) and have a rugged west coast, with sheer, 100-metre high cliffs and many furnas (sea caves) hewn by the sea and the wind. The east coast is gentler, and the formation of dunes and beaches is due to the protection afforded by forest and scrub formations.
Although the Rías Baixas has an oceanic climate—with high rainfall and moderate seasonality—the archipelagos of the Park have a subhumid Mediterranean climate with Atlantic influences. There is less rainfall than along the coast, as the low altitudes do not pose an obstacle for clouds, and in summer, rain is scarce. The Cíes Islands has an average annual rainfall of 1,000 mm. The average annual temperature ranges between 13–15 ºC, with little variations in temperature. The prevailing winds in summer are northerly, while they’re southwesterly in winter.
The flora in the Cíes Islands is dominated by Tasmanian blue gums (Eucalyptus globulus) and maritime pines (Pinus pinaster), which together cover a quarter of the islands. Portuguese crowberry (Corema album) and spiny thrift (Armeria pungens) can be found, while the predominant vegetation is gorse (Ulex europaeus). The dunes are well preserved and the seabeds are rich, with corals and more than 200 species of algae.
In terms of the fauna in the Cíes Islands, there are many seabird colonies—which are extremely important worldwide—, such as that of the common shag (Phalacrocorax aristotelis) or the Caspian gull (Larus cachinnans). It is the perfect spot for nesting, wintering and resting during migration for birds, as well as birdwatching for humans. There is also an important colony of reptiles and many marine species (cetaceans and fish).
The marine environment represents approximately 85% of the Atlantic Islands of Galicia Marine-Terrestrial National Park. The warm surface water pulled by the Gulf Stream, tidal amplitude and local upwelling (a phenomenon that brings nutrient-rich water to the surface during the summer) encourage the development of numerous habitats. Many organisms adapt to extreme changes and live in the rocky communities of the intertidal zone; these are the mussels (which occupy a large area), goose barnacles (which are very exposed to battering by sea waves) and the limpets (which attach themselves to rocks in order not to dry out). In the subtidal zone, the brown algae forests stand out, with species exceeding two metres in height. All of them form an ecosystem that provides food and shelter for other marine species: spider crabs, conger eels, Mediterranean rainbow wrasses, velvet crabs, octopuses, etc.
In the sea, the National Park’s main mobile seabeds are of sand, gravel and maerl (coarse shell gravel)—sedimentation areas which are also found in the muddy areas of Cíes Lake. On sand bottoms, there is an abundance of bivalves (scallops and queen scallops, as well as clams, cockles and razor clams), flatfishes that blend into the bottom (plaice, ray, cuttlefish and turbot) and a rich interstitial fauna that lives between the grains of sand. In contrast, gravel bottoms are made up of the remains of shells and molluscs, and are where microalgae and species such as scallops, variegated scallops and razor clams live. Lastly, maerl bottoms are made up of calcareous algae that accumulate—although only those in the top section are alive—and species such as the banded carpet shell, rayed artemis and long snouted lancetfish, as well as the early stages of many other species can be found.
Cíes Lake is also known as Lagoa dos Nenos and represents a unique ecosystem on the archipelago. It is located between the islands of Faro and Monteagudo; an artificial dike and Rodas Beach separate it from the sea. On its sandy, muddy bottoms, aquatic plants (with flowers) grow, forming veritable underwater meadows, which serve as spawning and breeding grounds for different species. The abundance of food and shelter in the lake is conducive to the appearance of many species: pollacks, eels, Mediterranean rainbow wrasses, conger eels, grey mullets, Ballan wrasses or mojarras, for example .
Among terrestrial ecosystems, the rugged coastal cliffs, subject to the impact of the wind and the sea, stand out. The Cíes Islands are the perfect nesting site for seabirds, but are also a habitat with tough conditions. The living conditions on the dunes and beaches—subjected to wind action, high levels of sun exposure and high salinity—are the reason for the scarcity of native forests and why most of the island is covered by scrub.
On the cliffs, there’s only room for vegetation that can survive in hostile environments with the impact of the wind, the salinity of the sea and the bird colonies nesting under the overhangs. One strategy for plants to survive here and offer greater wind resistance is to adopt a padded shape. The most noteworthy species in these environments are sea fennel, Calendula suffruticosa (subespecies algarbiensis), sea thrift and garden angelica, where the cormorants build their nests.
Plant species on the beaches and dunes develop strategies to deal with the high levels of sun exposure, the scarcity of nutrients, the instability of the ground, salinity and the wind. To survive in such harsh conditions, the plants bury their roots in the sand, which has a two-fold purpose: searching for sustenance and taking root, to prevent the wind from carrying them away. It is worth pointing out that there are communities of European beachgrass, field pennycress mallow bindweed, sand couch-grass, curry plant and Portuguese crowberry—a shrub which has become a symbol of the Cíes Islands, as there is an important community of it on the dunes (where the only population of spiny thrift in Galicia is also found).
On this archipelago, the development of arboreal vegetation is slowed down by environmental conditions, and it is only in the most sheltered areas of the east coast that you can find small groups of bay laurel, Pyrenean oak, willow and elder trees. Most of its land area is covered by shrub formations such as heather, blackthorn, asparagus, fern and Montpellier cistus, osyris and gorse (subespecies latebracteatus).
If the variety of plant species is wide, the variety of animal species is not far behind. With regard to invertebrates, there are endemic species among the orders of Blatoptera (cockroaches), Coleoptera (beetles), Dermaptera (earwigs), Lepidoptera (harlequin butterfly and Old World swallowtail) and Orthoptera (grasshoppers and crickets).
Low soil moisture and the absence of permanent watercourses make amphibians scarce. On San Martiño Island, you can find the fire salamander, while the Iberian painted frog is critically endangered on the archipelago. In contrast, this climate is especially conducive to reptiles. In the Cíes Islands, ocellated lizards (the largest in Europe, measuring 18 cm without its tail) can be found in great abundance. Another common reptile which has colonised the islets is the Iberian wall lizard. The slowworm and the western three-toed skink—common in the Park—are lizards which have tiny and atrophied legs, while the Bedriaga’s skink—“endangered” according to the Red List of Amphibians and Reptiles in Spain—is exclusive to this archipelago.
Most of the mammals in the Park are not native to the island. They were introduced by humans and pose a real threat (wildcat and American mink) to some native species. It’s also common to find small rodents (house mouse, wood mouse, brown rat and black rat), bats (common pipistrelle, serotine bat and greater horseshoe bat) and other mammals such as the European rabbit, European hedgehog, greater white-toothed shrew and European mole.
But without a doubt, birds are the centre of attention in the Atlantic Islands of Galicia National Park. The abundance of resources, the scant human presence and the availability of nesting sites are factors that favour their settlement, and being the perfect home and transit point for many species is driving birdwatching tourism. In terms of seabirds, here you’ll find the largest concentration of yellow-legged gulls (with about 20,000 breeding pairs) and common shags (about 1,000) in the world. The latter is categorised as “endangered” according to the Red List of Birds in Spain and the European storm petrel is considered by it as “vulnerable”. Hundreds of great cormorants use the archipelago as a roosting site in winter, a time when the Northern gannet can often be found, while in summer the Sandwich tern and the Balearic shearwater can be seen.
Waders (common sandpipers, herons, egrets, turnstones and curlews) are common in Cíes Lake, intertidal pools, beaches and rocky areas. Likewise, there are many lands birds that nest on the archipelago despite its small size. Among the birds of prey, you’ll find the northern goshawk, common buzzard, common kestrel, European nightjar, peregrine falcon and Alpine swift. Small birds (warblers, tits, blackbirds, woodpigeons, finches, turtledoves and greenfinches) are very abundant among the trees.
