El Cachucho Marine Protected Area: Mapping the Submarine Seamount Landscapes off Asturias

El Cachucho is best known for being Spain's first exclusively marine protected area, a designation that set a milestone for offshore conservation in the country. The seamount is celebrated for its complex geomorphology, including incised submarine canyons, rocky outcrops, sediment waves, and megaripples that shape distinct deep-sea habitats. Its biological richness, sustained by high primary productivity on the northern Iberian shelf, makes it a focal point for marine research and a recognized hotspot of deep-sea biodiversity in the southeastern Bay of Biscay.

The scientific history of El Cachucho began in the 1930s, when French oceanographer Edouard Le Danois conducted research cruises aboard the vessel Président Théodore Tissier between 1934 and 1939. His work revealed the existence of the bank that now bears his name, documenting its unusual character within the Cantabrian Sea.

For decades afterward, the feature remained largely unexplored, even though it lies within Spain's Exclusive Economic Zone only about 30 nautical miles from the coast of Asturias and sustains significant fishing activity. The ECOMARG research project, focused on the northern Iberian shelf, became a turning point by documenting the area's elevated biodiversity, geological complexity, and productivity. This growing understanding of the area's ecological value ultimately led to its designation as a Natura 2000 Site of Community Importance and Spain's first exclusively marine protected area, an institutional milestone in the broader development of Spanish marine conservation. The bank's geological origins are tied to compressive tectonic processes during the Paleogene, when imbricated thrust structures lifted the seafloor to form the present-day seamount.

El Cachucho's landscape is entirely submarine, yet it reads like a mountain range hidden beneath the sea. The seamount rises out of the deep Bay of Biscay, climbing from roughly 4,500 meters depth toward shallower plateau areas of around 500 to 600 meters. The bank stretches about 57 kilometers in length and 17 kilometers in width along an elongated east-west axis, forming a distinctive escarpment within the Cantabrian Sea.

The surrounding continental margin amplifies the area's dramatic character. The northern Iberian shelf is unusually narrow, giving way to a steep continental slope incised by deeply carved submarine canyons. Notably, the Llanes and Lastres submarine canyons frame the central section of the studied platform, acting as the principal conduits that funnel sediment from the continent down into deep basins. The bank itself features four major geomorphological components: prominent rocky outcrops with strong relief, alternating hard lithologies, massive rocky outcrops, lower-relief rocky areas with thin sediment cover, and a range of sediment forms, including flat unconsolidated sedimentary floors, sediment waves, and sand ridges. Together, these varied substrates create a richly textured seafloor that contrasts sharply with the deeper, flatter abyssal areas nearby.

El Cachucho hosts an unusually diverse set of marine ecosystems for an offshore environment. The combination of a narrow but productive continental shelf, steep slopes, incised canyons, and an elevated seamount creates a mosaic of habitats. Hard substrates, including prominent rocky outcrops and massive rocky areas, support communities adapted to strong currents, while lower-relief rocky zones with thin sediment cover offer different ecological niches. Together with megaripples, sand ridges, and unconsolidated sedimentary plains, the seamount supports a varied benthic environment.

The high primary productivity of the northern Iberian shelf feeds into the food web on and around the bank, sustaining a complex biological community. Le Danois Bank acts as both a refuge and a meeting point for species from deeper and shallower environments, contributing to its strong biodiversity signal. This productivity and habitat heterogeneity made the area a natural candidate for marine protection as part of the Natura 2000 ecological network.

El Cachucho is recognized for its rich fauna, including communities typical of both deep and intermediate waters of the southeastern Bay of Biscay. The seamount's elevated plateau and surrounding slopes host diverse benthic and demersal species groups, supported by the high biological productivity driven by the narrow but productive northern Iberian shelf. The bank has long been associated with commercial fisheries, including traditional Asturian fishing grounds referenced locally as the caladero El Cachuchu.

Research efforts by the ECOMARG project have documented the area's elevated biodiversity relative to surrounding seafloor, with species assemblages shaped by rocky outcrops, canyon walls, and sediment plains. These varied habitats create conditions where cold-water corals, deep-sea invertebrates, and demersal fish species can coexist across relatively small spatial scales.

El Cachucho's designation as a Site of Community Importance under the European Natura 2000 framework established a new chapter in Spanish marine conservation, marking the first time Spain created a protected area focused exclusively on marine territory, rather than coastal or partially marine reserves like Doñana, Cabrera, or the Atlantic Islands of Galicia. This designation recognized the seamount's ecological importance, its role as a reservoir of biodiversity, and the need to safeguard deep-sea habitats from pressures including commercial fishing.

The conservation framework protects a complex set of benthic habitats, including rocky outcrops of varying relief, sediment-dominated areas, megaripple fields, and canyon geomorphologies. By safeguarding these features, El Cachucho contributes to the long-term preservation of biodiversity in the southeastern Bay of Biscay and provides a reference point for future offshore marine protection efforts in Spain and across Europe.

El Cachucho carries a strong regional identity among Asturian fishing communities, where it has long been known by the local name caladero El Cachuchu, referring to a productive fishing ground. The feature's formal scientific name, however, reflects the legacy of French oceanographer Edouard Le Danois, who introduced it to the broader scientific community through research cruises in the 1930s. This dual naming captures the area's identity as both a local working fishery and an internationally recognized deep-sea ecosystem of European conservation importance.

El Cachucho stands out as Spain's first exclusively marine protected area, an institutional milestone for offshore conservation in the country. Its elongated, east-west submarine seamount shape, combined with deeply incised canyons such as Lastres and Llanes, defines one of the most distinctive seafloor landscapes of the Cantabrian Sea margin. The protected area safeguards a varied suite of deep-sea habitats, from rocky outcrops with strong relief to megaripple fields and sediment plains, sustaining high biodiversity driven by the productivity of the northern Iberian shelf.

El Cachucho is a fully submerged marine protected area located about 30 nautical miles off the Asturian coast, and is not a typical visitor destination. Seasonal conditions of the Cantabrian Sea influence the character of any offshore activity in the area, with calmer summer months generally offering more workable conditions for research cruises and marine excursions, while the rougher winter sea state reflects the energetic Atlantic weather patterns that shape this stretch of coastline year-round.