Maritime-Terrestrial National Park of the Atlantic Islands of Galicia

As its name indicates, the sea plays a fundamental role in this natural space, where it constitutes approximately 85% of the protected area. The seabed is one of the main reasons why these islands were declared a National Park, and the sea and its proximity greatly influence even the terrestrial ecosystems. The marine area of the Atlantic Islands has a high ecological value and a great attraction both for its landscapes and for its wealth of fauna and flora. The biodiversity that characterises this environment is a consequence of its particular oceanographic conditions and the multiple habitats found there, which create ideal conditions for the development of a wide variety of communities.

The Gulf Stream reaches the coasts of Galicia, warm surface waters coming from the Caribbean that greatly soften the climate of the region, so that the average temperature of the surface waters in Galicia is 14ºC, compared to the 5ºC of the North American coast at the same latitude.

Tides are oscillatory movements of the ocean waters that alternately produce a rise in sea level, called high tide, and a fall in sea level, called low tide. This phenomenon is caused by the gravitational pull of the sun and especially the moon on the earth and its water masses. On our coast, a high tide and a low tide alternate approximately every 6 hours and 12 minutes, so that we have two high tides and two low tides every day. The amplitude of the tide (the difference between the average level and the maximum or minimum) reaches 4 metres here. These periodic variations have a great impact on the organisms living in the coastal zone, which have to adapt to the drastic change in their living conditions every six hours.

The richness of the islands’ waters is based on a local upwelling phenomenon. During the summer, the prevailing winds cause the surface water to be pushed out of the estuaries, and the space it leaves behind is taken up by deep cold water that rises towards the coast. The upwelling water is rich in nutrients, which are available to the organisms that live in the illuminated area, including the microalgae that form the basis of the food chain. Thus, there is a significant increase in the populations of these plants and the rich marine fauna they feed.

In the rocky communities there is a great variety of habitats which, together with the large amount of oxygen and organic matter available due to the turbulence of the water, explains the great specific diversity of these environments.

In the intertidal (the area between the highest and lowest tide levels of the year), there are large areas dominated by mussels (Mytilus galloprovincialis) and, in the areas most exposed to the onslaught of the sea, barnacles (Pollicipes cornucopia), on a base of sea acorns of the genera Balanus and Chthamalus.

A good example of the adaptations of the animals living in this area to avoid drying out at low tide is the limpets (Patella spp.): they attach themselves so tightly to the rock that the seal is airtight and water remains on the inside; when the tide comes in they start to move slowly in search of food, but when it goes out they attach themselves again at the same point.

In the permanently submerged subtidal, the forests of large brown algae stand out, as they are one of the communities with the greatest specific richness on the Spanish coast. They are formed by Saccorhiza polyschides, Laminaria ochroleuca and Laminaria hyperborea, large algae species of up to 2.5 m in size. As if they were large trees, they allow a multitude of animals and plants to live among them and on them, forming a true underwater forest. Here we can find nécoras (Necora puber), octopus (Octopus vulgaris), conger eels (Conger conger) and many other species that find food and shelter in these communities.

In areas where sedimentation predominates over erosion, we find bottoms with mobile substrates, which can be, depending on the size and composition of the particles that form them: muddy, sandy, gravel, gravel… In the waters of the National Park, the main mobile bottoms found are sand, maërl and gravel, although in the bottoms around Cortegada and in Lake Cíes there are also muddy areas. All of them are characterised by the fact that the waves and currents constantly remove the surface layer of sediment.

On the sandy bottoms the algae are predominantly microalgae, although other species anchor themselves on isolated rocks among the sand. As far as fauna is concerned, sandy populations of bivalve molluscs such as the scallop (Pecten maximus) or the common scallop (Aequipecten opercularis) dominate. Also characteristic are flatfish that mimic the bottom or bury themselves slightly, such as plaice (Platichthys flesus) or rays (Raja spp.). In addition to all these organisms, the sandbanks are home to a tiny and rich interstitial fauna that lives in the tiny gaps between the grains of sand.

The maërl beds are composed of the calcareous algae Lithotamnion corallioides and Lithotamnion calcareum, in the form of more or less free, branched and strongly calcified arbuscules several centimetres wide. The accumulation in sedimentary levels of this structure, where only the algae of the surface layer are alive, provides an intricate network of refuges that allows these bottoms to harbour a great diversity of animals. Among the animals that live here are the blonde clam (Venerupis romboides) and the watch clam (Dosinia exoleta). Among the fish, the sand eel (Ammodytes tobianus) stands out. In addition to these species, the maërl shelters the juvenile stages of many other species such as the cuttlefish (Sepia officinalis) or the spider crab (Maja squinado).

The gravel beds are made up of large remains of mollusc shells, especially bivalves and gastropods, which form a layer several centimetres thick in which most of the animals that live here are buried. Vegetation is limited to microscopic algae or small encrusting algae on fragments of shells or on the shells of animals still alive. A varied fauna is hidden here: scallops (Pecten maximus), scallops (Chlamys varia), razor clams (Ensis spp.),…

In the Cíes archipelago, between the islands of Monteagudo and Faro, there is a shallow saltwater lagoon with a high biodiversity, called Lagoa dos Nenos. In addition to a variety of different environments of intertidal and subtidal sands and rocks, there is an area of muddy-sandy bottoms where two species of Zostera, aquatic flowering plants that form true underwater meadows, grow. The zosterales serve as spawning and frying grounds for fish and other groups, where the conditions favour their use for holding the eggs of different species, and also a high density of larvae and juveniles, which find here a large amount of food, an area of calm water and a hiding place and protection from predators. The conditions of the lake also favour fish fauna, and without having to enter the water, we can observe a good representation of this diversity walking along the dike that limits it: mullets (Chelon labrosus), mojarras (Diplodus vulgaris), maragotas (Labrus bergylta), and even eels (Anguilla anguilla), etc.

The islands that form part of the National Park have an important wealth of flora and fauna, due, among other things, to their variety of ecosystems (Atlantic and sub-Mediterranean coastal scrubland, cliffs, beaches and dunes). The Habitats Directive protects a series of habitats for which measures must be established to guarantee their conservation. The following habitats of Community interest are found on the islands.