The Costa Quebrada Geopark is a mosaic of natural environments, including marshes, beaches, dunes, cliffs, riverbanks and coastal oak forests. Together, these ecosystems support rich and diverse biodiversity and act as an essential ecological corridor for numerous species of flora and fauna.

Further inland, limestone outcrops shelter the last remnants of coastal oak forests—vestiges of past climatic conditions. Pine plantations within the Liencres dune system have given rise to a unique forested landscape, while hay meadows, dry-stone walls and hedgerows reflect the region’s traditional agricultural and livestock practices.

The coastal cliffs of Costa Quebrada are of outstanding geological and ecological value. They have been shaped by active marine erosion acting on Cretaceous and Paleogene sedimentary formations, resulting in intertidal platforms, abrasion terraces, sea cliffs and scree slopes.

Constant exposure to salt spray, strong winds and temperature fluctuations has allowed halophytic and psammophytic vegetation to colonise these cliffs. Notable species include Crithmum maritimum, Armeria pubigera and Limonium humile. In splash zones, specialised lichens and mosses thrive.

Bird species such as the European shag (Gulosus aristotelis) and the European storm petrel (Hydrobates pelagicus) benefit from protection under the EU Birds Directive. The cliffs also support endemic invertebrates, contributing to the ecological connectivity of the Cantabrian coast.

The beaches of Costa Quebrada, including Valdearenas, Canallave and Arnía, are constantly shaped by sedimentation, erosion and coastal sediment transport. They support ephemeral habitats of high ecological value, such as embryonic, mobile and stabilised dune systems (habitat types protected under the EU Habitats Directive: 2110, 2120, 2130).

Dune vegetation includes pioneer species adapted to salinity and sand burial, such as Ammophila arenaria, Elymus farctus and Medicago marina. These plants stabilise the substrate and facilitate ecological succession towards more mature plant communities.

These areas are critical for vulnerable species such as the Kentish plover Charadrius alexandrinus, whose breeding success depends on undisturbed beaches with low levels of human pressure. Vegetation loss, uncontrolled trampling and coastal development constitute direct threats.

In inland areas of the Geopark, particularly at higher elevations or on wetter soils, remnants of Atlantic deciduous forests persist, including oak woods Quercus robur, chestnut groves and mixed broadleaf forests. These landscapes are vestiges of the extensive Eurosiberian forests that once covered much of the Cantabrian region and continue to play a key role in supporting biodiversity.

Beneath the canopy, relict ferns, hygrophilous mosses and a rich assemblage of saproxylic invertebrates indicate a high degree of ecological maturity.

Although some forest areas have been fragmented or replaced by Pinus radiata and Eucalyptus plantations, the restoration of native deciduous species and the enhancement of ecological connectivity remain central objectives of Natura 2000 conservation plans.

Costa Quebrada’s wetlands include small streams, temporary ponds, and marsh areas such as the reed beds (Phragmites australis) around the Pas estuary and the Mogro marsh. Despite their limited spatial extent, these habitats are ecologically vital: they regulate hydrology, filter pollutants, and provide refuge for high-value species.

Notable fauna includes sensitive amphibians such as the Palmate Newt em Lissotriton helveticus and waterbirds like the Grey Heron em Ardea cinerea and the Water Rail em Rallus aquaticus. Riparian zones host characteristic vegetation, including Salix atrocinerea, Alnus glutinosa, and Carex– and Juncus-dominated communities, protected under habitats 91E0* (alluvial forests) and 6430 (humid meadows).

These ecosystems are particularly vulnerable to hydrological alterations, diffuse agricultural pollution, and invasive species such as Baccharis halimifolia and Cortaderia selloana. Ecological restoration and the long-term protection of riparian corridors are therefore crucial.

Costa Quebrada’s rural landscape, historically shaped by extensive agriculture and livestock grazing, forms an agroecological mosaic of high biodiversity value. Hay and pasture meadows, living hedgerows, dry-stone walls (locally known as morios), and linear copses provide shelter for open-habitat birds, small mammals, and a rich diversity of butterflies and pollinators.

Semi-natural habitats such as Atlantic humid meadows (6510) and oligotrophic grasslands (6230*) depend on traditional practices including crop rotation, the use of native breeds, and late mowing. Botanical highlights include Orchis mascula, Leucanthemum vulgare, and Trifolium pratense.

Loss of agricultural activity, land-use intensification, or abandonment leads to habitat degradation, the spread of invasive species, and landscape homogenisation through forest plantations. Sustainable management is essential to maintain ecological connectivity and to preserve this intangible rural heritage.

The Geopark’s limestone formations and karst processes have created underground systems of outstanding scientific and ecological interest. Caves and sinkholes, both coastal and inland, maintain stable microclimates and humidity, supporting highly specialized fauna with remarkable levels of endemism and troglomorphic adaptations.